ISRM 2023 - PUBLICATIONS

T15: Rock and rock mass propertiesSrđan KOSTIĆJaroslav Cerni Water Institute, SerbiaEstimation models for deformability of marlstones based on their physical and mechanical properties and for variable load rangeIn present paper we establish the correlation between the field determined values of elasticity E and deformability modulus D of marlstones and their laboratory determined physico-mechanical properties. Laboratory results which are taken into consideration are the following: unit weight, moisture content, uniaxial compression strength, cohesion, friction angle, maximum and minimum pressuremeter load range, as input parameters, and elasticity and deformability modulus as output parameters. Statistically significant correlations are determined by applying multiple linear regression method and ANOVA test. Established correlations indicate that both for E and D properties for undisturbed rock samples (cohesion, unit weight, uniaxial compression strength) do not have significant effect, while friction angle has strong positive effect both on E and D. Mostiure content have negative effect on E and D. Minimum/maximum load stress have opposite effect on E and D, meaning that deterioration of rock mass in situ with the increase of stress has negative effect on D. | pressuremeter, marlstone, elasticity modulus, deformability modulus
T15: Rock and rock mass propertiesJørgen Steen STEENFELTCOWI, DenmarkOptimization of UCS testing of limestone rockAssessment of strength and stiffness of rock is difficult due to the huge variability in these parameters. This is due to the often very heterogeneous nature of the rock. As large-scale testing is often prohibitively expensive or difficult to achieve in practice, the assessment relies on testing smaller specimens, typically from boreholes. The current paper provides guidelines for evaluation and interpretation of rock strength and stiffness based on UCS, Point Load and Brazil tests as a function of size, height/diameter ratio of specimen and rock strength. Based on currently available standards and literature the empirical conversion equations for tests with non-standard D and H/D values are referenced and evaluated. | Limestone strength, UCS, height/diameter ratio, non-standard specimens
T15: Rock and rock mass propertiesYadong XUE (1), Lushan SHU (1), Kai SHEN (2), Yongfa GUO (3)1: Department of Geotechnical Engineering College of Civil Engineering, Tongji University, Shanghai, China; 2: School of Civil Engineering, Central South University, Changsha, China; 3: China Railway Eryuan Kunming Survey, Design and Research Institute Co., Ltd, Kunming, ChinaStudy on the mechanical characteristics of rock-concrete Brazilian disc based on DEMThe rock-concrete interface is usually considered the weakest structural zone in tunnel lining structures. To study the tensile failure of the rock-concrete interface, the Brazilian splitting tests were carried out on sandstone-concrete Brazilian discs using the digital image correlation (DIC) system. The laboratory tensile strength and failure process are consistent with numerical simulation. Then, the tensile behavior of the interface with different roughness was simulated using MatDEM software. Results show that the tensile strength of rock-concrete disc is insensitive to the sawtooth number. The tensile strength increases with increasing sawtooth angle due to increasing total contact area and interlocking effect. When the sawtooth angle is more than the critical value, the tensile strength increases rapidly due to the formation of the breaking sawtooth. | Rock-concrete interface, Brazilian splitting test, Interface tensile failure, Interfacial roughness, MatDEM
T15: Rock and rock mass propertiesDavide ELMOUniversity of British Columbia, CanadaThe Bologna interpretation of rock bridges: what is real and what has the potential to be real?This paper presents a provocative discussion on the subject of rock bridges and, by extension, on the topic of rock mass strength. We believe that there cannot be innovation in rock engineering if we are not open to looking at problems from a different perspective, even though that means abandoning practices that are considered industry standards for better or worse. The Bologna Interpretation of rock bridges states that one can only know where a rock bridge is once one measures it. And to measure it, you need the rock mass to fail. This interpretation highlights the indeterministic nature of rock bridges: they become real only when we look at them. Before failure, there are no actual rock bridges, only potential rock bridges which exist everywhere at once. | Rock Bridges, Bologna Interpretation, Rock Mass Strength
T15: Rock and rock mass propertiesXiwei ZHANG, Lei SHINortheastern University, Shenyang, ChinaDevelopment and functional verification of an ultra-deep drilling core geological environment true triaxial apparatusGiven that the drilled core diameter decreases with increasing depth and there is no true triaxial apparatus for testing the complete stress–strain behavior and long-term deformation behavior of small-sized cores, a geological environment true triaxial apparatus was developed. The apparatus was mainly designed to obtain the complete stress–strain curves of hard rock specimens measuring 25 mm×25 mm×50 mm, while also considering the measurement of long-term deformation. This device focuses on solving technical problems such as inaccurate measurement of specimen deformation, low stiffness of the apparatus, mutual interference between pressure chamber oil pressure and actuator pressure.The deformation behavior of Xiling ultra-deep drilling cores was measured using this apparatus. | ultra-deep drilling core; true triaxial test; complete stress–strain; time-dependent failure
T15: Rock and rock mass propertiesJian YANG (1,2), Li-Yun FU (1,2)1: Shandong Provincial Key Laboratory of Deep Oil and Gas, China University of Petroleum (East China); 2: School of Geosciences, China University of Petroleum (East China)Temperature- and pressure-dependent dynamic and static elastic moduliThe differential characteristics of temperature- and pressure-dependent dynamic and static elastic properties are investigated in a range of temperature and confining pressure for porous sandstone. Results show that the dynamic and static Young’s moduli increase against confining pressure, whereas the dynamic one decreases and the static one increases against temperature, respectively. The ratios of static and dynamic elastic properties for the Young’s modulus decrease against the ratio of thermal stress to confining pressure. The opposite result is observed for the Poisson’s ratio. We demonstrate that the progressive crack closure of primary microcracks associated with the limited expansion of cement material is dominant in the range of experimental pressure and temperature, instead of the development of new microcracks during thermal treatments. Therefore, the axial and radial strains decrease with increasing pressure and temperature, which reduces the static Poisson’s ratio but increases the static Young’s modulus. | Dynamic and static moduli, Temperature and pressure dependence, Microcracks, Strain amplitudes
T15: Rock and rock mass propertiesZhen YE (1), Qian LIU (2), Qiang XU (1), Xiujun DONG (1), Feng PU (1)1: State Key Laboratory of Geohazard Prevention and Geoenvironment Protection, Chengdu University of Technology, China; 2: Graz University of Technology, AustriaA practical approach to determining the basic friction angle of natural and rough discontinuities in carbonate rock slopesThis study investigates the suitability of an adapted portable shearing box to measure the shear-induced dilation of a discontinuity and how the basic friction angle can be reliably derived from the shear data with dilation. Results show that samples with significant roughness are required. The reliability of the resulting basic friction angle depends on both the magnitude of the applied normal loads and the horizontal base length used to calculate the angle of dilation. We have developed data processing techniques to identify the optimal horizontal base length. The proposed method was successfully applied to estimating the basic friction angle of discontinuities that control the blocks stability in Kaili carbonate slope. | Adapted portable shear box, horizontal base length, dilation angle, basic friction angle
T15: Rock and rock mass propertiesHasan ARMAN, Safwan PARAMBANUnited Arab Emirates University, College of Science, Geosciences Department, Al Ain, United Arab EmiratesStudy on the relationship between uniaxial compressive strength and elastic properties of limestone with various sample diameterUniaxial compressive strength (UCS), elasticity modulus (E) and Poisson’s ratio (υ) are critical design parameters in engineering. This study investigates the relationship between the UCS, Et (slope of the line tangent at 50% of the UCS) and υ of limestone core with various diameters. Core samples with a diameter of 25, 38, 48, 54 and 63mm were prepared for the UCS tests with strain gauges. The results were analyzed using linear regression between UCS and Et and υ with different sample diameters. The regression analysis results show that the Et has weak to strong positive and negative correlations with the UCS for sample diameter. The correlation between the υ and UCS is variably weak to strong for sample diameters of 38, 63, 25, 48 and 54mm. In general, the mean Et and υ decrease with increasing sample diameter increments, however, no meaningful trends are found for the UCS case. | Uniaxial compressive strength, Modulus of elasticity, Poisson’s ratio, Limestone, Sample diameter
T15: Rock and rock mass propertiesRabin Kumar SAMAL, Gangavarapu Teresa DES DE MONA, Sunita MISHRADepartment of Mining Engineering, IIT Kharagpur, IndiaBehaviour of a pre-defined crack propagating under dynamic tensile loading conditionCrack propagating at the rock-tool interface is of paramount importance while designing an excavation process. The present study aims to analyze the behavior of a crack propagating in brittle material like sandstone rock in comparison to ductile material like Aluminum alloy. A three-dimensional finite element model of split Hopkinson pressure bar setup was developed with a pre-cracked dog bone-shaped specimen to understand the behavior of crack using two non-linear strain rate dependent constitutive models, i.e., the Johnson-Cook model and Drucker Prager model. The numerical results were first validated with the experimental ones and then the effect of the crack parallel to the loading direction was studied under dynamic tensile loading conditions. The results show that the peak stress values are more at the center and tip of the crack for aluminum alloy than for the intact aluminum alloy specimens. However, it is completely opposite for sandstone rock. | Brittle material, dynamic loading, FE model, pre-crack, SHPB, tensile loading
T15: Rock and rock mass propertiesAbhishek MOHAPATRA, Anjali KUMARI, Sunita MISHRADepartment of Mining Engineering, IIT Kharagpur, IndiaNumerical Analysis of Thermo-Mechanical Characterization of Indian Sandstone under Dynamic Compressive Loading ConditionIt is quite impractical to ascertain the in-situ mechanical behavior of rocks subjected to high temperature and high confining pressure under dynamic loading conditions. Hence, the present study aims to numerically determine the thermo-mechanical properties of Kota sandstone rock under dynamic compressive loading conditions using a split Hopkinson pressure bar (SHPB) device. Thereafter, a numerical model is developed similar to the experimental setup used for the dynamic characterization of Kota sandstone using a commercially available finite element (FE) software package, ABAQUS. The specimen size of Kota sandstone was modeled with a 54 mm diameter and 0.5 slenderness ratio as taken by Mishra et al. (2019). A thermally sensitive strain rate-dependent constitutive model is adopted to validate the numerical parameters with experimental results tested at room temperature. The effect of the temperature and loading rate on the mechanical behavior of the Kota sandstone rock is studied numerically and stated herein. | Dynamic Loading, Finite Element, SHPB, Strain Rate Dependent, Temperature, Drucker-Prager
T15: Rock and rock mass propertiesMeng-Chia WENG (1), Hoang-Khanh LE (1), Hung-Hui LI (2), Chih-Shan LEE (1), Chia-Chi CHIU (3)1: National Yang Ming Chiao Tung University; 2: National Defense University; 3: National Taipei University of TechnologyInfluence of microscopic composition on the strength of rock-like materials under various loading ratesThis study investigated the dynamic strength and failure mode of rock-like materials considering the effect of microscopic composition and loading rate. A series of uniaxial compressive tests and SHPB tests were conducted on specimens, which contained 40% and 60% grain contents by volume and two types of cementation material (gypsum and weak gypsum). The results indicate a lower grain content and, correspondingly, a higher matrix volume, yields a higher quasi-static strength. The dynamic strength is related to not only the grain content but also the degree of grain breakage. Moreover, inter-granular fractures mainly occur under quasi-static compressive conditions, and the failure mode becomes trans-granular when the strain rate is high. Specimens with lower grain content exhibited fewer fractures and larger fragments than those with higher grain content. Considering the influence of matrix property, the weak-gypsum-cemented specimens exhibited higher dynamic increase factor and lower strength than the gypsum-cemented specimens. | Rock-like material, spilt-Hopkinson pressure bar (SHPB) test, dynamic strength, strain rate
T15: Rock and rock mass propertiesDeepanshu SHIROLE (1), Gabriel WALTON (2), Ahmadreza HEDAYAT (3), Sankhaneel SINHA (4)1: Indian Institute of Technology Delhi, India; 2: Department of Geology and Geological Engineering, Colorado School of Mines, Golden, USA; 3: Department of Civil and Environmental Engineering, Colorado School of Mines, Golden, USA; 4: Department of Geology and Geological Engineering, Colorado School of Mines, Golden, USAEvaluation of the dilatant behavior of a crystalline rock using full-field optical imaging and ultrasonic monitoringExperimental study of rock specimens under uniaxial stress path has shown that ultimate failure in rocks occurs after the onset of crack coalescence associated with dilatancy. Typically, rock dilatancy is represented by estimation of averaged specimen-scale total volumetric strains (ε_v). However, in previous studies, full-field ε_v (i.e. variations throughout a specimen) has not been rigorously analyzed. Accordingly, in this work, the full-field deformation measurement method of 2D-DIC (digital image correlation) is implemented to characterize evolution of dilatative (ε_v<0) and contractive (ε_v>0) strains in Stanstead granite specimens under uniaxial loads. In-sync, ultrasonic monitoring was also conducted to non-destructively monitor damage in the specimen. Results showed that full field strains evolve in a heterogeneous manner, with some regions showing dilation, and some showing contraction. Also, increases in ultrasonic amplitude during the initial stages of testing were shown to be linked to the occurrence of contractant strains. | mage correlation, ultrasonic monitoring, dilatancy, contraction
T15: Rock and rock mass propertiesDanielle PAJIEP (1,2), Jian-Fu SHAO (2), Nathalie CONIL (1), Mountaka SOULEY (1), Philippe GOMBERT (1)1: National Institute for Industrial Environment and Risks; 2: University of LilleHydromechanical characterization of Château-Landon chalk behaviorThe paper deals with the effect of water saturation degree on the stress–strain response of a high-porosity and pure chalk, the Chateau-Landon chalk. A general experimental methodology is presented, including hydrostatic and triaxial compression tests performed under drained conditions with loading paths combining variations of stresses and water saturation degree to characterize the hydromechanical behavior of this porous material. | Chalk, hydromechanical behavior, water saturation, porous
T15: Rock and rock mass propertiesLichun JIA, Qicong XU, Chongjun HUANG, Lei LI, Xiao WEI, Changhong ZHOUDrilling & Production Technology Research Institute, CNPC Chuanqing Drilling Engineering Company Limited, People's Republic of ChinaThe dynamic tensile strength and failure characteristics of transversely isotropic shale under impact Brazilian testTo comprehensively understand the failure behaviors under dynamic loading, a series of SHPB tests are conducted on deep Longmaxi shale under different loading rate at seven loading-bedding angles β. The results indicate that both static and dynamic BTS increase with the angle β. But the dynamic BTS are far greater than the static. However, as the loading rate increases, the anisotropic index decreases gradually. There is a positive correlation between dynamic BTS and loading rate, which is that the dynamic BTS increases with loading rate and the relation between dynamic BTS and loading rate is fitted by a power function with correlation coefficients R2 higher than 0.92. The failure results show that there are four typical fracture patterns, which are central tensile failure as β=0° and β=90°, bedding activation shear failure as β=15°, non-central arc fracture at β=30° and 45°, mixed mode fracture as β=60° and 75°, respectively. | Longmaxi shale, transversely isotropic, split Hopkinson pressure bar (SHPB), dynamic Brazilian tensile strength (BTS), failure patterns
T15: Rock and rock mass propertiesNeil BAR (1,2), Wulf SCHUBERT (1)1: Graz University of Technology, Austria; 2: Gecko Geotechnics LLC, Saint Vincent and the GrenadinesEvaluation of different methods for determining rock masses stiffnessSurface and underground excavations in rock are designed for ensuring stability. In many tunnel, underground cavern and rock slope projects, designing to acceptable deformation limits or tolerances is just as critical as stability. Understanding rock mass stiffness and deformability becomes an integral part of ground characterization and subsequent design. Deformation moduli for rock masses are often estimated using empirical methods that may have been developed from limited data, specific ground conditions, and provide a single result representing the behavior of an isotropic, homogeneous rock mass. However, most rock masses are heterogeneous or anisotropic, and deformation moduli can vary significantly depending on the loading direction. This paper reviews available empirical methods for evaluating deformation moduli and compares them with an observational model from monitored slope deformations in siltstones, sandstones and quartzite at a surface and underground mine in Australia. | Rock mass stiffness, empirical methods, deformation modulus
T15: Rock and rock mass propertiesPetar HRŽENJAK (1), Ivana DOBRILOVIĆ (1), Dražen NAVRATIL (2), Biljana KOVAČEVIĆ ZELIĆ (1)1: University of Zagreb, Faculty of Mining, Geology and Petroleum Engineering, Croatia; 2: Croatian Geological Survey, CroatiaShear strength determination of very rough and partially filled extension fractures in thick-bedded and karstified limestonesExtension fractures that appear as very rough and irregular and with or without infill material, are common in thick-bedded and karstified limestones for which present-day methods for shear strength estimations are inappropriate. With the aim of determining the shear strength of such discontinuities, field research was carried out, in which large samples of blocks with discontinuities, as well as samples of filling material were prepared, on which then detailed laboratory tests were performed. Based on the obtained results, a modification of Barton’s JRC-JCS empirical model was made in such a way that the friction angle of the built-in filling material in the case of discontinuity with a filling was applied, instead of the residual friction angle. In addition, the joint contact coefficient (JCC) was introduced as the measure of the actual contact area between discontinuity walls by means of which the normal stress on the discontinuity surface can be corrected. | extension fractures, shear strength, friction angle, joint roughness coefficient, joint contact coefficient, Barton’s empirical model
T15: Rock and rock mass propertiesYudhidya WICAKSANA (1), Suseno KRAMADIBRATA (2), Seokwon JEON (3)1: Institut Teknologi Bandung, Indonesia; 2: Bumi Resources Minerals, Indonesia; 3: Seoul National University, Republic of KoreaEstimation of cutting force considering intermediate dynamic rock strength using multiple linear regressionThis paper estimates pick cutting force using multiple linear regression considering rock properties determined under intermediate dynamic loading. Existing theoretical and empirical works on rock cutting performance have focused on cutting parameters and static rock mechanical properties. Even though rock cutting is a dynamic event, prediction models that consider dynamic rock properties have not been explored. Earlier research has demonstrated that the cutting mechanism in rock operates under intermediate dynamic conditions in which the strength would improve compared to its static state. Multiple linear regression analyses were performed to estimate the mean and maximum cutting forces of unrelieved cutting tests. This study compared the performance of the suggested models to that of the models produced by Evans, Goktan, and Roxborough & Liu. Statistical analysis showed that the suggested models have a lesser mean squared error to the data population than the theoretical models. | Rock cutting, Cutting force, Pick cutter, Intermediate dynamic loading, Multiple linear regression
T15: Rock and rock mass propertiesSakshi ROHILLA, Resmi SEBASTIANIndian Institute of Technology Ropar, IndiaStudy of stress-dependent dynamic properties of jointed rock using resonant column apparatusField stress conditions have a significant impact on the mechanical characteristics of jointed rock masses. This paper investigates and discusses the effects of joint spacing and confining pressure on the dynamic properties of a jointed rock mass. The RCA was used to test jointed gypsum material at varied confining pressures and strain amplitudes. The normalised shear modulus and material damping ratio curves for various joint spacings and confining pressures have been produced. The modified hyperbolic and Ramberg-Osgood models were used to fit curves based on experimental data collected at various shear strain amplitudes and confining pressures. This study presents the best-fitted parameters showing the link amongst shear modulus and shear strain, in addition to damping ratio and shear strain for varied joint spacing. The eminence of confining pressure on shear modulus and damping ratio at various strain levels has been studied using the power function. | Jointed rock, Shear modulus, Damping ratio, Confining pressure, Joint spacing
T15: Rock and rock mass propertiesSair KAHRAMAN (1), Egemen SAYGIN (2), Mustafa FENER (3)1: Hacettepe University, Turkey; 2: RPM Global-Turkey; 3: Ankara University, TurkeyThe influence of microwave treatment on the Cerchar abrasivity of igneous rocksThis study investigates the effect of microwave treatment on the Cerchar abrasivity index (CAI) of igneous rocks such as granite, syenite, and gabbro. First the mineral contents and percentages of each rock were determined. Then, microwave treatment was applied on the specimens broken in the indirect tensile strength for 180s at the microwave powers of 2 kW and 6 kW. The evaluation of the test results shows that the CAI values of the specimens decrease with increasing microwave power. The CAI losses increase generally with the increasing surface temperature and the microwave power depending on the mineral contents. Concluding remark is that microwave treatment decreases the CAI values of igneous rocks. However, further study should be carried out to determine the CAI loss for different rock types at different exposure times and microwave powers. | Cerchar abrasivity, Igneous rocks, Microwave treatment, Mineral contents
T15: Rock and rock mass propertiesKai ZHANG (1), Ling ZHU (2), Li CHENG (3), Qingchao LYU (4), Yaoru LIU (1)1: Tsinghua University, People's Republic of China; 2: Hydropower Engineering Technology Research Center, Academy of Science and Technology, China Three Gorges Corporation; 3: China Renewable Energy Engineering Institute; 4: Powerchina Northwest Engineering Corporation LimitedEffect of normal stress on dynamic friction weakening of granitic rock joints under cyclic shearThe friction strength evolution of rock joints subjected to cyclic dynamic loads is very vital to the safety and stability assessment of rock engineering during earthquakes and rock bursts. In this paper, cyclic shear experiments under different normal stress were carried out for granite joints based on a shaking table apparatus. The frictional behavior under cyclic shear, especially the dynamic evolution of friction strength, was investigated and the effect of normal stress on friction strength weakening was quantified. Based on experimental results, a hysteresis model is used to characterize the dynamic friction behavior of planar joints under cyclic shear. This model relates the evolution of friction strength to the number of cycles of cyclic shear. As the normal stress increases, the strength weakening ratio increases correspondingly, while the critical number of cycles (at which the residual strength is reached) remains essentially unchanged. | Rock joints, Dynamic friction, Cyclic shear, Normal stress
T15: Rock and rock mass propertiesZhiqiang LIU (1,2), Linlin WANG (1,2), Shihui YU (1,2)1: China University of Petroleum-Beijing, People's Republic of China; 2: State Key Laboratory of Petroleum Resources and Prospecting, China University of Petroleum, Beijing, China 2 China University of Petroleum, Beijing, ChinaLow-temperature Thermal diffusion in RocksAt low temperature, frost weathering due to the freezing/thawing process of pore water can fracture bedrock permafrost, which is of crucial importance in engineering. We focus on the low-temperature thermal diffusion that is primarily fundamental but poorly investigated. The experiment and simulation investigations are conducted on sandstones subject to low-temperature conditions. It shows that the heat capacity of sandstones is more sensitive to temperature at the condition of the low temperature than that at the condition of the high temperature. The thermal conductivity of dry sandstone decreases with temperature at the condition of high temperature. However, it reveals that the thermal conductivity increases with temperature at the condition of low temperature. Besides, the temperature evolution curve for the water-saturated sample remains quasi-constant with the time when the phase transition occurs, which is governed by the pore-size distribution. | Heat transfer, Low temperature, Phase transition, Thermal conductivity
T15: Rock and rock mass propertiesXunhui XU (1), Weiren LIN (1), Han BAO (2), Peijie YIN (2)1: Kyoto University; 2: Chang'an UniversityFlow simulation in digital rough fractures by considering anisotropic roughness and geometrical combinationsAnisotropic flow behavior in rock fractures is playing an important role in resource exploitation and engineering. To better understand the relation between flow behavior and geometrical features of fractures, digital fractures with 3 roughness were generated based on the spectral method. Simulation was conducted on 3 constant velocity inlets. From the results, flow behavior in 4 fracture pairs all show anisotropy in opposite directions. Different flow behaviors of the walls swapped fracture pairs indicate the influence of normal vectors of fracture asperities. Ratios of the roughness parameter M between upper and lower fracture walls are correlated to flow pressure gradient. | Rock fracture, flow simulation, anisotropy, pressure gradient, roughness
T15: Rock and rock mass propertiesPeiwang CAO (1), Tao ZHOU (2), Rui LI (1), Jianbo ZHU (2)1: State Key Laboratory of Hydraulic Engineering Simulation and Safety, School of Civil Engineering, Tianjin University, Tianjin, China; 2: Institute of Deep Earth Sciences and Green Energy, College of Civil and Transportation Engineering, Shenzhen University, Shenzhen, ChinaEffect of loading rate on dynamic mixed mode I/II fracture behavior in rockDynamic mixed mode I/II fracture of rock is quite common in rock engineering due to various dynamic disturbances. However, the understanding of rate effect of mixed mode I/II fracture behavior in rock is still at its infancy. To investigate mixed-mode fracture under different loading rates, the split Hopkinson pressure bar tests were conducted on cracked straight through Brazilian disc sandstone specimens. The results show that the crack propagation velocity, mode I and mode II stress intensity factors, dissipated energy increase with increasing loading rate. The effect of loading rate on crack propagation path is slight. The changes in micromorphology of rock may be the main reason for the rate effect of fracture. Findings in this work can help understand the dynamic mixed mode I/II fracture in rock engineering subjected to high loading rates. | Mixed mode I/II fracture, Stress intensity factor, Rate effect, Rock material
T15: Rock and rock mass propertiesSamer ABOU KHEIR (1), Andrea BROGIATO (1), Patrick LIGNIER (2), Angelo LAMBRUGHI (3), Gabriele DE CARLI (4), Mark DIEDERICHS (5), Ivan CHING (6), Damiano FRONTINI (7)1: Tractebel Engineering S.A, Gennevilliers, France; 2: Tractebel Engineering S.A, Lyon, France; 3: Webuild S.p.A, Milan, Italy; 4: Webuild S.p.A, Rome, Italy; 5: Queen’s University, Kingston, Canada; 6: Snowy Hydro Limited, Cooma, Australia; 7: Future Generation Joint Venture, Cooma, AustraliaAssessment of the creep behavior of siltstone for the Snowy 2.0 hydropower station using multistage uniaxial and triaxial creep testsThe creep behavior of the siltstone rock type formations at the site of the Snowy 2.0 hydropower station was studied through multistage uniaxial and triaxial creep tests. The tests were conducted for up to 4 months to assess the effect of creep on the siltstone and to evaluate the impact on the short-term parameters. Samples were collected from boreholes located 650-850 meters beneath the surface from the Ravine Beds Unit formation and found to be composed of siltstone with interbedded sandstone (70/30% average). The siltstone was characterized by medium strength, a stiff matrix, and low porosity. The results of the creep tests showed negligible secondary creep deformations after full development of the primary stage. Additionally, the effect of confining pressure on creep behavior and deformation amplitude was also investigated. These tests provide valuable information to better understand the behavior of the siltstone rock type and its impact on underground excavation. | multistage triaxial creep test, multistage uniaxial creep test, siltstone, hydropower station, creep behavior
T15: Rock and rock mass propertiesAndrew Garnet CORKUM (1), Derek KINAKIN (3), Diego MAS IVARS (2)1: Dalhousie University, Canada; 2: BGC Engineering Inc, Canada; 3: SKB and KTH, SwedenIntact Strength Determination of Rock Containing Mesodefects using the Leeb Hardness TestThe strength of rock blocks containing structural flaws and defects, such as veins and healed fractures (mesodefects) is particularly important for sparsely jointed rock masses under high stress. The conventional UCS test is often unsuitable for providing an accurate measure of the intact strength for rock containing mesodefect and it is difficult to conduct tests on suitably large specimens to account for mesodefects. The Leeb Hardness (LH) test is proposed to provide a quantifiable estimate of intact strength for mesodefected rock. The LH test is a lightweight, compact rebound test that has been correlated to rock strength with a large database (~400 test records) of various rock types over a wide strength and hardness range. The effects of conducting LH tests in the proximity of mesodefects has been examined and the LH test has been used in this study to estimate the true intact rock strength of defected rock cores. | Leeb Hardness test, defects, intact rock strength, DFN
T15: Rock and rock mass propertiesMilorad JOVANOVSKI, Jovan Br. PAPIC, Igor PESHEVSKIUniversity Ss. Cyril and Methodius, Faculty of Civil Engineering, Republic of North MacedoniaPhysical modelling of bimrocks in large scale direct shear apparatusComplex geological mixtures as bimrocks, composed of core block inclusions randomly distributed in a weaker matrix, are challenging issues for a proper characterization in a large scale relevant for rock mass range, as the overall behavior is strongly influenced by the presence of the rock fragments and by their volumetric block proportion. The article presents results from their physical modelling and tests in a large-scale direct shear box with dimensions 1,0x1,0x0,6 m, loaded with stresses in large span. The mixtures of blocks and matrix are modelled for values of volumetric block proportion of 5%, 15% and 35%. Results confirm that higher contents of volumetric block proportion lead to higher angle of internal friction and lower value of apparent cohesion, while the time of failure is longer for a higher volumetric block proportion. | Bimrocks, volumetric block proportion, physical modeling, shear strength, time of failure
T15: Rock and rock mass propertiesTimothy Robert Michael PACKULAK, Émélie GAGNON, Samuel Keith WOODLAND, Jennifer Jane DAYDepartment of Geological Sciences and Geological Engineering, Queen's University, CanadaApplication of Digital Image Correlation for Analysis of Anisotropic Materials Under TensionTensile strength of rock and similar materials is a critical material property in rock engineering design. Anisotropic materials do not necessarily follow the behaviour as originally assumed when the Brazilian Tensile Strength test was created; therefore, additional care is required when analyzing tensile strength measurements of these materials. This study presents guidelines and recommendations for the analysis of strain accumulation in disc specimens with anisotropic geological fabrics using 2-dimensional digital image correlation. In addition, strain maps of specimen faces generated with digital image correlation are used to corroborate the mechanistic behaviour of a proposed three part anisotropic tensile strength criterion. | Brazilian Tensile Strength, Laboratory Testing Procedures, Anisotropic Geological Fabric, Foliation, Digital Image Correlation, True Tensile Strength
T15: Rock and rock mass propertiesSair KAHRAMAN (1), Ahmet Niyazi CANPOLAT (2), Mustafa FENER (3)1: Hacettepe University, Ankara, Türkiye; 2: General Directorate of Mineral Research and Explorations, Ankara, Türkiye; 3: Geological Engineering Department, Ankara University, Ankara, TürkiyePredicting strength loss of igneous rocks treated with microwave energyThis paper investigates the predictability of the strength loss of igneous rocks treated with microwave energy. First microwave treatment tests were performed at 6 kW power for the duration of 120s on the core samples of nine different igneous rocks such as granite, syenite and gabbro. Then uniaxial compressive strength (UCS) tests were carried out on the hot specimens. Mineralogical analysis, density and porosity tests were also performed on the samples. The data were evaluated using multiple regression analysis and an estimation equation with very high correlation coefficient was derived for the strength loss. The equation includes UCS, maximum surface temperature, quartz plus feldspar content and porosity values. The statistical test showed that the equation was valid. It was concluded that the derived equation could be used for the estimation of the strength loss of igneous rocks treated with microwave energy. | Igneous rocks, Microwave treatment, Strength loss, Regression analysis
T15: Rock and rock mass propertiesMarte GUTIERREZ (1), Daisuke KATSUKI (1), Runar NYGRAARD (2)1: Colorado School of Mines, United States of America; 2: Oklahoma University, United States of AmericaShear failure and fracturing of horizontally layered shaleUnderstanding the mechanical behavior of shale formations is becoming increasingly important. Shales are essential in oil and gas production from tight unconventional resources. In geological carbon sequestration of CO2, shales typically form the caprock for geological storage. Fractures provide high permeability pathways for fluid flow and leakage for shales because of their low permeability. Shales have a layered structure with discontinuities parallel to the bedding plane, which can result in distinct anisotropy in their hydro-mechanical behavior. This paper aims to understand better the effects of intrinsic structural anisotropy from their layered structure on shale shear failure and fracturing behavior. Triaxial shear tests at constant confining stress were conducted on shale samples drilled horizontally parallel to the bedding plane. A new mechanism is proposed to explain the formation of shear/extensional fractures along bedding planes when shale samples are sheared under significant constant confining stress with the major principal stress perpendicular to the bedding plane. | Bedding planes, Layering, Shear Failure, Fracturing, Leakage
T15: Rock and rock mass propertiesVladimir FRIDSami Shamoon College of Engineering‎, IsraelEffect of rock stiffness change on acoustic emissionIt is known that the ratio of rock stiffness around the mine workings and the stiffness of the ‎surrounding strata has a crucial meaning for rock stability in the close vicinity of the ‎underground excavation. Significant resources were invested for the research aiming to ‎understand the failure mechanism using acoustic emission (AE) to evaluate the relationship ‎between the parameters of AE and crack/fracture dimension/scale to determine statistical ‎regularity of AE appearance before oncoming rock collapse and features of acoustic wave ‎attenuation during its propagation via rock massive. However, the methodology of the ‎rock stiffness assessments based on the AE parameters is still lacking. The paper considers the physical basis for applying AE for stiffness assessment ‎in underground conditions. | acoustic emission, rockburst, rock stiffness
T15: Rock and rock mass propertiesMin GAO, Xu ZHU, Chengguo ZHANG, Joung OHUniversity of New South Wales, AustraliaA modification of nonlinear Forchheimer’s coefficient for fracture flow during shearThis study introduces a new hydromechanical model to estimate both shear and nonlinear flow behaviours of a single rock fracture, taking into account the effects of fracture surface morphology on the fracture flow behaviours. The model incorporates a multi-scale roughness shear constitutive model that considers the adhesion and abrasion wear theories to predict the shear behaviours of a fracture due to shear deformations. The fracture permeability is estimated using the Forchheimer-based equation, which accounts for the combined effects of the fracture void spaces, aperture distributions, and fluid flow tortuosity. Laboratory shear-flow experiments under different hydraulic pressures and normal loading conditions are conducted to validate the proposed model. The model is in good agreement with experimental data and can be applied to sheared aquifers. | Shear-flow model, single fracture, surface roughness, multi-scale roughness, nonlinear flow
T15: Rock and rock mass propertiesGreg GAMBINO (1), John P. HARRISON (2)1: University of Toronto, Canada (now at WSP Canada Inc.); 2: University of Toronto, CanadaTemperature-dependent strength of ice-filled discontinuities in frozen and thawing rock massesThis paper presents new results regarding the strength of ice-filled discontinuities. Careful laboratory testing using prepared core specimens containing ice in artificial discontinuities allowed the indirect tensile strength of ice-rock interfaces to be determined at different temperatures. These results were combined with those for shear strength published by others in 2000, to extend the shear strength data into the tensile regime. The combined results suggest a linear Coulomb criterion with no tensile cut‑off is appropriate for both the shear and tensile regimes at −2.5 and −5.0°C. Two regression models were investigated, one extending the shear data into the tensile regime, and the second combining the indirect tensile and shear data with the shear data being used to inform the relation through Bayes’ rule. These analyses confirm the robustness of the indirect tensile testing and provide a predictive strength criterion for rock engineering design in frozen and thawing discontinuous rock masses. | ice-filled discontinuities, tensile strength, strength criterion, Bayesian regression
T15: Rock and rock mass propertiesNatália de Faria SILVA, Eduardo Antonio Gomes MARQUES, Carolina Crissafe dos Santos LEMOS, Carolina de Souza Pires COSTAUniversidade Federal de Viçosa, BrazilProposition of an accelerated cycling procedure for rocks with low porosityA relevant method for study weatherability of rocks is the accelerated alteration simulation which intends to describe susceptibility to weathering and its products. Nevertheless, it can be difficult to set which methodology should be adopted, as the initial state of sample must be reconciled with the environment to which it’ll be exposed, so that, in experimental time scale, it’s feasible to observe aspects of increasing alteration and modification in properties. In a weatherability study of a metamorphosed hydrothermalized basalt with very low initial porosity, an accelerated cycling throughout immersion in sodium sulfate was adopted. Even subjecting the rock to 100 cycles, samples have only shown signs of no significant modification of physical properties. To produce substantial weathering change, a much larger number of cycles would be required, so some modifications to the test procedure are proposed, allowing the execution of a greater number of cycles without increase in duration of the experiment. | Weatherability, weathering, accelerated cycling, alteration simulation
T15: Rock and rock mass propertiesJohn William de Bradnee MARTIN (1), Alexander KLUCKNER (1), Gerold LENZ (2), Thomas MARCHER (1)1: Institute of Rock Mechanics and Tunnelling, Graz University of Technology, Graz, Austria; 2: iC consulenten ZT GesmbH, AustriaBack-analysis of rock mass parameters at the Semmering Base Tunnel based on the convergence confinement methodThe monitoring of geodetic targets installed at the tunnel lining provides reliable information on the system behaviour. At the Semmering Base Tunnel (SBT), engineers use the software package TUNNEL:Monitor to visualise monitored displacements and to make short-term predictions ahead of the face. A toolbox to apply the convergence confinement method (CCM) to the geodetic measurements has been incorporated into TUNNEL:Monitor for the purpose of back-analysing rock mass parameters post tunnel construction. This paper details the results of two case histories undertaken to assess the suitability of the back-analysis procedure implemented in TUNNEL:Monitor. Findings from the case studies confirm TUNNEL:Monitor is suitable for the back-analysis of rock mass parameters, provided the limitations associated with the procedure are well understood and the procedure is not extended beyond its applicability. | TUNNEL:Monitor, Semmering Base Tunnel, back-analysis, displacement monitoring, convergence confinement method, anisotropy
T15: Rock and rock mass propertiesMauro MUÑIZ-MENÉNDEZ (1), Ignacio PÉREZ-REY (2)1: CEDEX, Madrid, Spain; 2: University of Vigo, Vigo, SpainInfluence of the specimen slenderness on the direct tensile strength of rocksSome rock engineering design operations are mainly controlled by the tensile strength and deformability of the rock (i.e., critical span of excavations or hydraulic fracturing). The ISRM Commission on Testing Methods and the ASTM procedures recommend the use of cylindrical rock specimens, with height-to-diameter (H/D) ratio of 2.5 to 3.0 for direct tensile strength (DTS) determination, in a similar way as per UCS testing. Nevertheless, it is unclear how this ratio may affect the tensile strength of a rock when directly determined. In the present work, the authors performed some series of numerical simulations with a 3D distinct element code (3DEC), replicating DTS tests carried out on specimens presenting five H/D ratios (0.5, 1, 1.5, 2, 2.5, and 3). The study is complemented with laboratory DTS tests in granite. The results herein presented indicate that H/D ratios greater than one have almost negligible influence on DTS. | direct tensile strength, slenderness, suggested method, 3DEC
T15: Rock and rock mass propertiesAmin HEKMATNEJAD (1), Eduardo ROJAS (2), Alvaro PEÑA (3), Benoit CRESPIN (4)1: Pontificia Universidad Católica de Valparaiso, Chile; 2: CODELCO, Chile; 3: Pontificia Universidad Católica de Valparaiso, Chile; 4: University of Limoges, FranceSpatial modeling of rock strength heterogeneity and anisotropy using Universal Discontinuity index (UDi)Rock strength anisotropy and heterogeneity are two key properties of various types of rocks. Discontinuities are the most significant factor on the anisotropic and heterogeneous behavior of rock mass strength. In this study, Universal Discontinuity index (UDi) applied to spatial modeling of the anisotropic and heterogeneous behavior of rock mass due to presence of discontinuities around a tunnel for the prediction of the geometry of over-excavation. UDi is based on the state of the art of the rock mass characterization systems and rock failure criteria. More precisely, UDi combines the quantitative and measurable parameters of the discontinuity network including volumetric discontinuity intensity (P32), the orientation of the discontinuities, vectorial based criteria of Warburton for kinematic rock block failure, and Mohr-Columb criteria for shear failure analysis. The results of this are validated through comparison with observed over-excavation at field data. | Rock strength anisotropy and heterogeneity, Universal Discontinuity index, rock block failure, shear failure, over-excavation
T15: Rock and rock mass propertiesKiyotoshi SAKAGUCHI, Yuta SHIROSAWATohoku University, JapanSize effect and correlation with hardness of the microscopic fracture toughness of the minerals of graniteMicroscopic fracture toughness (MFT) tests on the minerals composing the Inada granite (quartz, K-feldspar, plagioclase, biotite) were conducted to elucidate the fracture phenomenon of rock. MFT tests were conducted with three cantilevered specimens of micrometer size. The MFT of mineral was in the order of quartz, plagioclase, K-feldspar, and biotite from the largest value. Those MFT were lesser than the macroscopic fracture toughness of the Inada granite evaluated by the SCB test. In addition, the mineral grain boundary MFT was smaller than the mineral MFT. We found no significant scale dependence for the MFT itself. It was suggested that macroscopic fracture toughness of Inada granite may be controlled by quartz, which has a large composition ratio and large MFT. Furthermore, it was clarified that the MFT of each mineral has a positive correlation with the Vickers hardness, which are indicators of the hardness of the minerals. | Microscopic fracture toughness, Mineral grain, Mineral grain boundary, Size effect, Hardness
T15: Rock and rock mass propertiesBunyuu HASEGAWA (2), Sota HIGASHI (1), Atsushi SAINOKI (1)1: Kumamoto University, Japan; 2: Tokyo University, JapanElucidation of microscopic stress state within surface asperities of a rock jointField observations suggest that the occurrence of fault-slip related seismicity in deep underground be affected by the non-linear and/or time-dependent behaviour of discontinuity surface asperities. The present study aims at investigating the strain and stress distribution of discontinuity surface asperities on a micro scale by conducting a uniaxial test in a micro-focused X-ray CT, analyzing the CT images with the digital image correlation method, and reproducing the experiment with numerical simulation in the framework of the discrete element method. The experimental result obviously shows strain concentration within asperities on the discontinuity, which is approximately 10 times as large as that in the matrix. Surprisingly, the numerical simulation shows an asperity to matrix strain ratio similar to the experiment, although the absolute value is different. It was then concluded that the difference is attributed to time-dependent and/or brittle failure behaviour of the highly stressed asperity. | Discontinuity asperity, DIC, micro-focused X-ray CT, DEM simulation
T15: Rock and rock mass propertiesLeona VAVRO (1), Martin VAVRO (1), Minami KATAOKA (2)1: The Czech Academy of Sciences, Institute of Geonics; 2: The University of Tokyo, Department of Systems InnovationDetermination of an empirical relations between mode I fracture toughness using CB and SCB specimens and Brazilian tensile strength of rocksFracture toughness (FT) expresses material resistance to crack propagation leading to its final macroscopic failure. Approximatelly 20 different laboratory methods are currently used for a mode I and mixed mode I/II FT rock testing. However, it is a well-known fact that, for the same rock, the mode I FT value varies when different specimen types are utilized. Moreover, the preparation of specimens for FT testing may be associated with difficulties in obtaining required notch dimensions. From this point of view, Brazilian tensile strength (BTS) represents an easily and quickly detectable parameter that can be applied for prediction of the mode I FT. In this contribution, the results of investigations of mutual empirical relationships between FT determined using CB and SCB tests, as well as among FT values obtained via these testing methods and BTS are presented. A total of 14 different rock types, mostly sandstones, were used for this research. | rock, mode I fracture toughness, CB specimen, SCB specimen, Brazilian tensile strength
T15: Rock and rock mass propertiesLiang ZHANG (1,2), Xiaopeng LI (1), Qingxin QI (1), Haitao LI (1)1: Deep Mining and Rockburst Research Institute, CCTEG Chinese Institute of Coal Science, Beijing, China; 2: State Key Laboratory Cultivation Base for Gas Geology and Gas Control, Henan Polytechnic University, JiaoZuo, Henan, ChinaCracking evolution for deep hard coal using X-ray in-situ micro-CT technology and fractal theoryRockburst poses severe threats to the deep mining of coal mines in China; however, the fracture mechanism of deep hard coal is still unknown. Hence, this paper focuses on the cracking evolution laws for deep hard coal with high-bursting liability utilizing X-ray in-situ micro-CT technology and fractal theory. The in-situ micro-CT scanning system and bursting liability indexes for deep hard coal are first introduced in this work. Then, the uniaxial compressive experiments for the coal samples using in-situ CT scanning are conducted. Furthermore, the crack initiation, propagation, and coalescence of coal are revealed based on the in-situ micro-CT scanning experiment results. The 3D digital core of coal is obtained; four typical parameters, including fracture volume fraction and fractal dimension in 2D and 3D, are used to characterize the fracture network evolution for deep hard coal during the progressive failure process. The findings are valuable in rockburst, damage, and fracture mechanics. | Deep mining, rockburst, hard coal, cracking evolution, in-situ micro-CT, fractal theory
T15: Rock and rock mass propertiesNazlı TUNAR ÖZCAN (1), Elif AVŞAR (2)1: Hacettepe University; 2: Konya Technical UniversityA Study on Dynamic Shear Properties of BimrockDynamic shear strength of rocks is of critical importance for rock mechanics and rock engineering applications. In this study, dynamic direct shear tests were carried out to investigate the dynamic shear strength of welded weak bimrocks and to determine the effect of volumetric block proportion (VBP) on dynamic shear behavior. For this purpose, artificial model bimrock specimens with different VBP were constituted, due to challenges in extracting undisturbed natural specimens. According to the results, most of the model specimens show strain hardening behavior after the dynamic shear failure occurs. The dynamic shear strength of specimens increases with the increase in the VBP values. In addition, the VBP of the shear failure surfaces at the end of the tests are obtained through digital image processing analyses. It is concluded that the VBP values of failure surfaces have an effect on the shear strength parameters as well as the overall VBP. | Bimrock, Dynamic Shear Strength, Dynamic Shear Test, Volumetric Block Proportion
T15: Rock and rock mass propertiesChangshuo WANG, Shigui DU, Weiming LIU, Rui YONG, Zhanyou LUOInstitute of Rock Mechanics, Ningbo University, Ningbo, Zhejiang, ChinaInvestigation on the influence of non-stationary trend on the shear strength of rock jointsThe non-stationary trend of rock joints significantly affects the shear strength of rock joints. Taking the least square fitting plane of a rock joint as a reference plane, two trend direction parameters α and β of the rock joint are proposed to characterize the non-stationary trend of rock joints quantitatively. α is the inclination angle of the rock joint along the shearing direction, and β is the deflection angle of the rock joint perpendicular to the shearing direction. Based on the trend direction parameters, the external normal and tangential stresses are decomposed into the normal and tangential stresses on the reference plane. Consequently, a rock joint shear strength model is established. Next, samples of different sizes are obtained from a large rock joint. Based on the established shear strength model, the shear strengths of the rock joint samples in different sizes under the influence of non-stationary trends are statistically analyzed. | Rock mechanics, rock joint, roughness, shear strength, non-stationary trend
T15: Rock and rock mass propertiesAbbas TAHERI (1), Roohollah SHIRANI FARADONBEH (2)1: Queen's University, Canada; 2: Curtin University, AustraliaFailure response of rocks under different cyclic loading historiesThe post-failure instability of rocks was investigated through an extensive experimental study under four different loading histories, including the monotonic quasi-static loading, single-level systematic cyclic loading (SLSCL), multi-level systematic cyclic loading (MLSCL), and post-peak cyclic loading (PPCL). The lateral strain-controlled and double-criteria damage-controlled testing methodologies were implemented for the experiment. A combined post-peak Class I-II behavior to different extents was detected for soft to strong rocks, while the unstable fracture propagation was more dominant for stronger rocks under monotonic loading. Additionally, rocks exhibited more self-sustaining behavior under MLSCL history with increasing the number of cycles before the failure point. On the other hand, the results of the SLSCL tests revealed that rock brittleness reaches its maximum value by applying systematic cyclic loadings at stress levels close to the monotonic strength. However, the effect of post-peak cyclic loading (PPCL) history on the post-failure response of rocks was negligible. | Post-failure, cyclic loading, damage-controlled, lateral strain-controlled
T15: Rock and rock mass propertiesYun ZHAO (1), Brijes MISHRA (2), Qingwen SHI (3)1: Department of Mineral Resources, Hubei Xingfa Chemicals Group Co., Ltd, Yichang, China; 2: University of Utah, United States of America; 3: Department of Mining Engineering, North China Institute of Science and Technology, Langfang, ChinaSize-dependent and Anisotropic Coulomb failure criterionThis paper proposes the size-dependent and anisotropic Coulomb failure criterion to describe the size effect and anisotropy of shale strength. The failure criterion assumes that cracks and bedding planes cause size effect and anisotropy. The failure criterion has six parameters, the cohesion, friction angle, scaling exponent related to crack and bedding plane. The cohesion decreases as rock size increases based on the scaling exponents while the friction angle is independent of rock size. This paper validates the failure criterion from three aspects. Strength data of anisotropic rock is collected from published research. The failure criterion “fits” the collected strength data of anisotropic rock. A bonded-particle model of shale is developed in PFC2D which explicitly includes cracks and bedding planes. The model strength fits well with the failure criterion. Finally, experiments conducted in shale rock validates the hypothesis that the variation of cohesion and friction angle with rock size follows the failure criterion. | Size effect, Anisotropy, Coulomb failure criterion, Griffith theory, Single plane of weakness model
T15: Rock and rock mass propertiesAnjan PATEL (1), Srikanth KANDALAI (1), Nithin Jacob JOHN (1), Shrirang PANDE (2)1: Visvesvaraya National Institute of Technology, Nagpur, India; 2: M/s Standard Precision Testing Laboratory, Khadgaon Road, Lava, Nagpur-23, IndiaEffects of weathering on geotechnical properties of basalt rocks from the Vidarbha region in Maharashtra, IndiaIt is well known that the degree of weathering largely affects the geotechnical properties of rocks. Study of rock properties vis-à-vis degree of weathering and the site-specific parameters obtained through recovered rock core pieces during drilling is supposed to be useful for various engineering purpose. A similar effort has been made in the present study. Bore logs data were collected for different sites from Vidarbha region in Maharashtra, India, where basalt rocks are encountered. Based upon field identification, extent of weathering in various rock core pieces collected from different depths in boreholes at different locations was identified along with the determination of RQD value. Further, variation of some rock properties (viz., density, water absorption value, and unconfined compressive strength) with depth was studied. Results obtained from the analysis are presented and discussed in this paper. | Basalt rock, Weathering, Depth, Unconfined compressive strength, Rock quality designation
T15: Rock and rock mass propertiesYota TOGASHI (1), Riho HIRASAWA (2), Masahiko OSADA (1)1: Saitama University, Japan; 2: Saitama University (presently Oriental Consultants), JapanA new simple shear test of rock prism specimen by torsional shearingThis study proposes a new simple shear test method by torsional shearing of rock prism specimens. In this test, multiple radially placed prismatic specimens are torsional sheared under normal load. To validate the test method, a torsional loading apparatus capable of carrying 50 kN normal load and 300 kN cm torque was prepared, and the proposed test was conducted using prismatic mortar specimens which strength are equivalent to soft rock (UCS < 25 MPa). The size of the prismatic specimen is 20 mm height, 20 mm width, and 70 mm depth. The stress-strain characteristics of the mortar specimens were consistent with the previously conducted trends in uniaxial compressive and tensile strength. Peak shear stress in simple shear tests at under 0.9 MPa normal stress conditions equals tensile strength. Almost equal tensile strength was obtained when compared to the results of the proposed test. | Simple shear, prismatic specimen, torsional shearing, soft rock
T15: Rock and rock mass propertiesManuel WINKLER, Thomas FRÜHWIRT, Thomas MARCHERInstitute of Rock Mechanics and Tunnelling, TU Graz, AustriaA theoretical framework for calibrating the transversely isotropic elastic rock parameters from UCS tests on cylindrical specimens using circumferential strain measurementsThe standard method for determining the set of five independent elastic constants of transversely isotropic rocks relies on the conduction of at least three UCS tests with directional radial strain measurements on samples with varying isotropy plane orientation. However, in many cases only averaged values for the lateral strains are available from chain extensometer measurements as commonly carried out in rock mechanics laboratories. Such measurement setups disregard the anisotropic deformational behavior of transversely isotropic rock samples which appears as a result of non-horizontal isotropy plane orientations. A direct utilization of averaged radial strains in the determination of the five independent parameters without further considerations is thus not possible. In this paper a possible scheme for the inclusion of circumferential strain measurement information in the determination of the elastic constants of transversely isotropic rocks based on UCS tests carried out on three samples with varying isotropy plane inclinations is presented. | UCS tests, transverse isotropy, elastic parameters, circumferential strain measurement, Poisson’s ratio
T15: Rock and rock mass propertiesRoberto TOMÁS (1), Miguel CANO (1), Luis F. PULGARÍN (1), Vicente BROTONS (1), David BENAVENTE (1), Tiago MIRANDA (2), Graça VASCONCELOS (2)1: UNIVERSIDAD DE ALICANTE, Spain; 2: ISISE, Departamento de Engenharia Civil. Universidade do Minho, PortugalPhysical-mechanical properties of a granite used in the UNESCO World Heritage of the north of Portugal after high-temperature pretreatmentThis paper studies the evolution of physical and mechanical properties of 46 cubic samples of a granite widely used in the UNESCO World Heritage of the north of Portugal pre-treated at different temperatures (between 105 and 700 °C) and cooled under different conditions (i.e., air-cooled and water-cooled). The results showed that specific gravity and mineralogy did not exhibit significant changes after the thermal pre-treatment. In contrast, density, porosity, ultrasonic properties, uniaxial compressive strength and elastic modulus showed important variations, mainly at temperatures higher than 500 ºC. The SEM analyses clearly show an increase in the density of cracks, as well as in the width and length of the cracks from 500 ºC. Furthermore, it was observed an amplification of the damage in those samples cooled by water immersion. These results are of relevance for the evaluation of the integrity level of buildings built using this rock after a fire. | thermal effect; physical properties; uniaxial compressive strength; elastic modulus; granite; cultural heritage
T15: Rock and rock mass propertiesJun ZHU (1), Jianhui DENG (2)1: Key Laboratory of Mountain Hazards and Earth Surface Process, Institute of Mountain Hazards and Environment, Chinese Academy of Sciences (CAS), Chengdu,China; 2: College of Water Resources and Hydropower, Sichuan University, Chengdu, ChinaThe combined effects of water saturation and strain rate on crack initiation and damage stress of rockHere, we reported a series of uniaxial compression and acoustic emission (AE) tests performed on dry and saturated marble at different strain rates, which offer new information on the combined effects of water saturation and strain rate on its crack initiation CI stress and crack damage CD stress. The test data show that the water saturation causes various reductions in the ratio of CI stress to peak stress NCI, while increments in the ratio of CD stress to peak stress NCD. This NCI reduction is due to the main water-weakening effect of pore water pressure, and the increase in NCD is caused by the additional vicious effect. The NCI of saturated marble shows a decreasing trend with increasing strain rates, while that of NCD remains nearly constant. By easily initiating more small defects, the strain rate effect can strengthen the NCI reduction and inhibit the NCD increase. | stress threshold; water saturation; strain rate; acoustic emission; dominant frequency
T15: Rock and rock mass propertiesLichun JIA, Hu DENGDrilling & Production Technology Research Institute, CNPC Chuanqing Drilling Engineering Company Limited, People's Republic of ChinaExperimental evaluation of anisotropic dynamic and static elastic modulus in deep Longmaxi shaleUnderstanding the anisotropic elastic properties of deep Longmaxi shale is crucial for analysis of wellbore stability and hydraulic fracturing in this reservoir. Here, the anisotropic dynamic and static elastic properties are measured under dry, soaked by water-based and oil-based drilling fluid conditions. The results show that the anisotropy parameters ε, γ and δ calculated from wave velocities are <<1 for dry or soaked samples, indicating that this shale is a weak anisotropic rock. And the dynamic Young’s modulus E11 substantially exceeds E33 in all cases and both increases with confining pressure. From compression tests, the static Young’s modulus E0°, E45°, E90° increase with confining pressure but decrease dramatically of soaked samples. In conclusion, the dynamic Young’s moduli exceed static values regardless of direction, confining pressure, dry or soaked condition. And factors affecting the anisotropy of deep shale include the lower amount of clay content and less clumped clay minerals bands. | deep Longmaxi shale, transversely isotropic, ultrasonic wave measurement, uniaxial and triaxial compression tests, dynamic elastic modulus, static elastic modulus
T15: Rock and rock mass propertiesLichun JIA, Qicong XUDrilling & Production Technology Research Institute, CNPC Chuanqing Drilling Engineering Company Limited, People's Republic of ChinaThe tensile strength and failure characteristics of transversely isotropic deep Longmaxi shale under Brazilian testA series of Brazilian tests are conducted to investigate the anisotropic tensile failure of deep Longmaxi shale. The results indicate that the anisotropic Brazilian tensile strength (BTS) of deep shale shows an ascend-slightly decline-ascend trend with loading-bedding angle β. Five tensile failure criteria are used to predict BTS and compared with experimental results, the order of reliability is N-Z criterion > H-B criterion > L-P criterion > SPW criterion > MSPW criterion. Observing from failure of shale specimens, there are four typical fracture patterns: central straight fracture at β=0° and 90°, bedding activation shear failure fracture as β=15°, non-central arc fracture at β=30° and 45°, mixed mode fracture as β=60° and 75°. Moreover, there is an inverse relationship between BTS and bedding activation fracture. The cumulative AE counts-time curve exhibits a stepped increasing mode while AE counts show a monotonic decreasing trend with angle β. | deep Longmaxi shale, transversely isotropic, Brazilian test, Brazilian tensile strength (BTS), failure patterns, AE characteristics
T15: Rock and rock mass propertiesSamad NARIMANI GHOURTLAR (1), Seyed Morteza DAVARPANAH (1), László KOVÁCS (2), Balázs VÁSÁÁRHELYI (1)1: Budapest University of Technology and Economics, Hungary; 2: RockStudy Ltd, Pécs, HungaryCharacterization of Poisson’s ratio and Elastic Modulus of granitic rocks: from micro-crack initiation to failureKey geomechanical parameters utilized in rock engineering include Young's modulus and Poisson's ratio. Uniaxial compressive test results are essential in the evaluation of these values. This paper aims to study the process of changes of Poisson’s ratio and Young modulus for intact rock during loading from micro-crack initiation to failure stage. Both Young’s moduli and Poisson’s ratio were calculated using the stress-strain curves. By using parametric investigation, the crack damage stress, determined for Poisson’s ratio-axial stress graphs. Also, this research outline the findings that the variations among the three Young's moduli and Poisson’s ratio estimated for each specimen and suggest the most effective approach for doing so. It was found, that the Poisson’s rate depends on the stress value: it is linearly increasing with increasing stress till the unstable crack propagation stress. Contrary to previous ideas, our results suggest that the Poisson’s ratio is not a constant for rigid rocks. | uniaxial compressive test, Poisson’s ratio, Young's moduli, rock mechanical parameters
T15: Rock and rock mass propertiesHaiyang ZHANG (1,2), Feiyang LIU (1,2), Jian LIU (1,2), Xingguang ZHAO (1,2), Ju WANG (1,2)1: Beijing Research Institute of Uranium Geology, Beijing, China; 2: CAEA Innovation Center for Geological Disposal of High-Level Radioactive Waste, Beijing, ChinaThermo-hydro-mechanical coupling Triaxial Test Method for Rock with Fracture and Its ApplicationAll kinds of fracture discontinuities in granitic host rock of high level radioactive waste (HLW) repository not only degrade the engineering characteristics of rock mass, but also constitute potential groundwater seepage channels and nuclide migration channels. During repository operation, the expansion and evolution law of host rock fractures under the coupling effect of radiation heat, groundwater and stress field is of great significance for the long-term safety assessment of the repository. In this context, a triaxial test method suitable for rock with single fracture under the condition of thermo-hydro-mechanical (THM) coupling is proposed, which solves the problem that the rock sample with fracture as initial defect is easy to be destroyed due to the changes of complex test conditions such as temperature, hydraulic pressure, confining pressure and axial load. | repository host rock, thermo-hydro-mechanical coupling, triaxial test, crack propagation
T15: Rock and rock mass propertiesSujeet BHARTI (1), Rakesh KUMAR (1), Debasis DEB (1), K. U. M. RAO (1,2)1: Indian Institute of Technology Kharagpur, India; 2: National Institute of Technology Rourkela, IndiaA Mathematical Model for Shear Stiffness and Dilation for Saw-Tooth Joints under CNL ConditionsAn extensive direct shear test program has been conducted on regular saw-tooth artificial joint samples under constant normal load (CNL) conditions. The analysis of shear data reveals that shear stiffness (k_ss=dτ⁄du) and dilation (ψ=dv⁄du), where τ and v are the shear stress and vertical displacement respectively, are not constants throughout the evolution of shear stress. Rather, it is clear that both the variables change non-linearly with shear displacements (u) and can be approximated by two-parameter hyperbolic function with respect to u. These parameters are estimated using regression analysis using the experimental data. From the functions k_ss (u) and ψ(u), a shear displacement exists at which the basic friction angle occurs. Also, it is found that this displacement occurs where contraction ends and dilation begins. Based on that, the dilatant behavior and evolution of peak shear strength can be described leading up to the determination of dilation angle at the peak stress. | saw-tooth joint, direct shear test, mathematical model, shear stiffness, dilation
T15: Rock and rock mass propertiesWalter STEINER (1), Fritz MADSEN (2), Jean-François MATHIER (3)1: B+S AG, Bern, Switzerland; 2: Consultant, ret. ETHZ. Adliswil, Switzerland; 3: Consultant, ret. EPFL, Avenches, SwitzerlandSwelling pressures of clay rocks from laboratory tests: experience and improvementsSwelling in underground works can cause severe problems during and after construction. Consequently, swelling potential must be identified and quantified prior to construction. ISRM recommendations exist but not all interpretations are included and not all applied testing procedures follow these recommendations. Swelling pressures are not only influenced by the testing procedure, but also by the sampling technique and the conservation, transportation, and protection procedure of the samples, as well as the lab equipment. The construction of the test apparatus and the testing procedure both influence the test results. Swelling pressures can be determined by confined swelling tests. However, for incremental loading and unloading tests, often called Huder-Amberg tests, the procedure to determine swelling pressures are not well defined and the authors noted large deviations to the results of swelling pressure tests. A different technique to determine the swelling pressure from the incremental test is presented. | swelling, clay rocks, shale, laboratory tests, tunnels, heave
T15: Rock and rock mass propertiesMengsu HU (1), Laura PYRAK-NOLTE (2)1: Lawrence Berkeley National Laboratory, USA; 2: Purdue University, USAThe Interplay between Geometry and THMC ProcessesEarth systems consist of materials with complex geometric features undergoing complex coupled thermal-hydro-mechanical-chemical (THMC) processes. These geometric features when combined with THMC processes govern the formation and transformation of rocks and thus understanding this coupling is essential for rock engineering activities. In this paper, we aim to address the following scientific questions by presenting a series of examples from numerical modeling and laboratory experiments: (1) How does fracture asperity geometry affect compaction and shearing that control single-fracture mechanical and flow properties? (2) How do intersections of fractures affect deformation, fluid flow and chemical reaction? (3) What controls key processes such as pressure solution during the formation of sedimentary rocks? Through these examples, we will show that it is important to properly address the complex geometry and coupled processes to understand evolving Earth systems to maximize their potential use for energy recovery and storage. | Geometry, THMC, Fractures, Interfaces, Pressure Solution, Earth Systems
T15: Rock and rock mass propertiesChongyuan ZHANG (1), Hongtao LIU (1), Ping ZENG (2), Yang XIA (2), Liang WEN (1), Bo ZHOU (1), Bao ZHOU (1)1: PetroChina Tarim Oilfield Company, Korla, China; 2: China University of Petroleum, Beijing, ChinaA statistical damage constitutive model based on residual strength and Drucker-Prager criterionThe HTHP (high temperature and high confining-pressure) triaxial compression test has been conducted on dolomite at 8000m deep in the Tarim Basin, China. We first study the characteristics of rock deformation based on the experimental results. An improved damage constitutive model is introduced to overcome the limitations inherent in the existing models which cannot accurately characterize rock residual strength after failure. The Drucker-Prager model serves the failure criterion of the ultradeep rock. The model is used to fit the experimental data and the results show a good agreement, which indicates that the improved model can be used to predict the mechanical behavior during the whole loading process. The model provides a theoretical knowledge of the mechanical characteristics of ultra-deep rocks in Tarim oil field. | Constitutive Model, Residual Strength, Drucker-Prager Criterion, High Confining-pressure, Statistical Damage
T15: Rock and rock mass propertiesManuel A GONZÁLEZ-FERNÁNDEZ (1), Ignacio PÉREZ-REY (1), Leandro R ALEJANO (1), José MURALHA (2), Seungki HONG (3), Ki-Bok MIN (3)1: Department of Natural Resources & Environmental Engineering, University of Vigo, Spain; 2: Concrete Dams Department, National Laboratory for Civil Engineering (LNEC), Lisbon, Portugal,; 3: Department of Energy Systems Engineering and Research Institute of Energy and Resources, Seoul National University, Seoul, Republic of KoreaDetermining the transversely isotropic elastic constants from strain data by means of different mathematical approachesMechanical properties of rocks with marked weak planes such as foliation, schistosity or bedding, are not isotropic. The deformability of these rocks is transversely anisotropic (TI), and, therefore, different axial strains are observed according to the load direction, being equal in directions within the weakness plane. Their elastic behavior is theoretically defined by five independent constants. In this study, a relatively large number of strain data sets collected from compressive tests on slate are used to estimate these constants. Two main approaches are followed. The first consists in solving the corresponding compliance matrix equation by means of the least square best fit multi-regression approach in groups of samples, which are then averaged. The second is based on minimizing the error in the stress invariant by means of a non-linear gradient algorithm. Results are analyzed aiming to learn how to manage strain variability in the process of TI elastic parameter estimate. | Transversely isotropic elasticity, Elastic constants, Slate, GRG algorithm
T15: Rock and rock mass propertiesReza MOTTAGHI, Zhongwei CHEN, David J. WILLIAM, Mehdi SERATIThe University of Queensland, Brisbane, AustraliaExperimental and Numerical Investigations on Bi-axial Loading of Sandstone Brazilian DisksThe behavior of sandstone Brazilian disks is investigated under loading in two perpendicular directions. The vertical force was applied at a rate of 200 N/sec while the horizontal load was adjusted to a predetermined ratio of the vertical load until the sample failure. This testing process was repeated for various ratios (including 0%, 10%, 20%, 25%, 33%, 40%, 45%, and 50%) and the failure of samples were captured using a high-speed camera at 25 kHz. While the superposition theory suggests that there will be no tension at the center of the disks in a biaxial loading mode for ratios of 33% and above, results suggest tensile crack occurrence for ratios up to 45%. The numerical results further show that there is always a tensile stress close to the Indirect Tensile Strength happening within the disks central line. It was also noted that if the material transitions into a plastic mode due to extremely high stress ratios, the induced tensile stress would be always considerably higher. | Bi-axial Brazilian tests, Indirect tensile test, Bi-axial loading, Finite element modeling
T15: Rock and rock mass propertiesLucía CONDE-FERNÁNDEZ (1), Víctor MARTÍNEZ-IBÁÑEZ (2), Martina-Inmaculada ÁLVAREZ-FERNÁNDEZ (1), María-Elvira GARRIDO-DE LA TORRE (2), Celestino GONZÁLEZ-NICIEZA (1), Carlos HIDALGO-SIGNES (2)1: University of Oviedo, Spain; 2: Universitat Politècnica de València, SpainEffect of temperature on the mechanical behavior and acoustic emission characteristics of a rock – like materialAcoustic Emission (AE) is a non – destructive testing technique that allows the recording of the elastic waves released during crack propagation when materials are subjected to different stresses. Most of the current research evaluates AE characteristics related to mechanically stressed materials. However, there are hardly any references to studies that target how thermal or thermos – mechanical stresses influence AE recordings. Consequently, an experimental campaign has been designed to characterize high–strength mortar specimens, subjected to different temperatures while performing simple compression tests and monitoring the AE. The research has allowed obtaining interesting results in line with the objectives set for this study. Thus, it has been possible to establish that: 1) temperature affects the simple compressive strength of the material studied, 2) the recording of AE associated with thermal stresses is possible and 3) the combination of thermal and mechanical stresses increases the recording of AE parameters. | Acoustic Emission (AE), thermo-mechanical stresses, crack propagation, temperature
T15: Rock and rock mass propertiesSarbartha SARKAR, Rakesh KUMARIndian Institute of Technology Kharagpur, IndiaCharacterization of Mobilized Cohesion, Friction and Dilation Angles of Brittle Rock During Plastic DeformationThe behavior of basalt rock in plastic region is investigated by tri-axial compression tests. Four sets of basalt rocks are tested using a servo-controlled universal testing machine (UTM) under three confining stress 2, 4, 6 MPa. This study generates valuable information of post-yielding parameters like cohesion, friction and dilation angles of brittle rocks and shows their behavior during plastic deformation. The analysis results show that in post peak region, the basalt rock is brittle in nature. It exhibits a negative exponential relationship of cohesion and dilation angle with plastic shear strain. However, the friction angle remains almost constant with increase of plastic shear strain. The existing dilation angle models of Zhao & Cai (2010) and Pourhosseini & Shabanimashcool (2014) are used for estimating the model parameters for basalt rock. It is found that Zhao & Cai (2010) is more aptly fitted for basalt rock. | Brittle rock, cohesion, peak dilation angle, plastic shear strain
T15: Rock and rock mass propertiesPeter ALLAN (1), Jean-Pierre BAUD (2), Robert HEINTZ (3)1: Pace Geotechnics, Morpeth, Northumberland, United Kingdom; 2: Eurogéo, France; 3: Eurasol, LuxembourgHard soil and rock classification – Pressuremeter data versus tests on samplesThis paper deals with the correlation between rock properties presented by Kanji (2014), Kanji & Leão (2020) on rock samples of a wide range of strengths, with the classification of indurated and rocky soils from pressuremeter diagrams by Baud & Gambin (2013), Baud (2021). Tests were carried out simultaneously on a same jobsite, and these two approaches contribute to the characterization of rock drillability, showing a certain degree of similarity between them. The relationship between the pressuremeter modulus of the rock mass (ISO 22476-5) and a Young's modulus usable for finite element software is a stumbling block for the validation of a rock model, which remains questionable, as the actual behaviour of the rock masses is highly non-linear. Neither in-situ expansion testing nor uniaxial compression testing directly measures a single modulus representative of the rock mass, so engineering practice is to apply one or more weighting factors, primarily considering the spacing and nature of fractures within the rock mass. | Rocks classification, High Pressure Pressuremeter Test (Dilatometer Test), Compression Strength, Ground Modulus, Drillability
T15: Rock and rock mass propertiesYousef NAVIDTEHRANI (1), Covadonga BETEGÓN (1), Robert W. ZIMMERMAN (2), Emilio MARTÍNEZ-PAÑEDA (2)1: University of Oviedo, Gijon, Spain; 2: Imperial College London, London, UKOn the crack initiation location in the Brazilian test: Griffith-based insightWe address the controversy surrounding the use of the Brazilian test to estimate the tensile strength of rock-like materials. Due to its indirect nature, the tensile strength is inferred from the critical load by assuming that cracking initiates at the centre of the sample. We combine finite element analysis with the failure envelope of the generalised Griffith criterion to establish the crack nucleation location, and map the conditions that result in the nucleation of a centre crack. The results reveal that the regime of validity of the Brazilian test is much smaller than previously assumed, with current practices and standards being often inappropriate. An experimental protocol is developed that enables obtaining a valid estimate of the material tensile strength, and a MATLAB App is provided to facilitate the uptake of this protocol. We demonstrate the usefulness of our protocol through examples of valid and invalid tests from the literature. | Rock mechanics, Brazilian test, Fracture, Finite element analysis, Griffith theory
T15: Rock and rock mass propertiesMasahiko OSADA, Koji OSAWA, Christina Putri WIDYANINGTYAS, Yota TOGASHISaitama University, JapanFundamental study on estimation of permeability at in-situ EDZ from pore air pressure responseIn this paper, we report the results of measuring the pore air pressure response at an isolated space in a rock block while pressure changes are given within a pressure range slightly less than atmospheric pressure. The transient decay method and the oscillation method were adopted to estimate the permeability in the laboratory. In transient decay method, the pressure outside of the rock block reduce from atmospheric pressure to 930 hPa, and the pore air pressure inside the block is monitored. On the other hand, the oscillation method applies a fixed amplitude and fixed frequency with a pressure of 900 to 950 hPa. After analyzing the recorded data, the estimated permeability values from two methods were compared with the permeability determined from measurements of flow rate through a sample under a constant pressure gradient. | In-situ permeability test, Transient pulse test, Pore air pressure oscillation method, Intrinsic permeability, Excavation Damaged Zone (EDZ)
T15: Rock and rock mass propertiesSamarjeet KUMAR, Aditi NUWAL, Shantanu Kumar PATELIndian Institute of Technology Kharagpur, IndiaUnderstanding the Microscopic Mechanisms of the bi-modular behavior of rockRocks when tested in both tension and compression show bi-modularity. Although the effect of all the factors contributing to the bi-modularity behavior is not fully understood, one of the main contributing factors is considered to be the presence of the micro-structure separating/joining the mineral grains. In this study, the effects of grain micro-structure on the modulus ratio are examined using the discrete element tool PFC2D for LdB granite and yellow sandstone. Extensive calibration was carried out to find out the intergranular micro properties of the mineral grains which produce the macroscopic response of the rocks. The role of inter-granular bond strength, initial microfractures present, and inter-granular bond stiffness were investigated. It was found that initial micro-fractures present in a rock sample is the main reason for producing the bi-modularity in rock and by considering it, crack initiation stress observed in the laboratory can be captured (~ 40% of UCS). | Rock bi-modularity, micromechanical grain properties, PFC, crack initiation stress
T15: Rock and rock mass propertiesMatej PETRUZALEK (1), Ali AMINZADEH (1), Vaclav VAVRYCUK (1,2), Zuzana JECHUMTALOVA (2), Petr KOLAR (2), Josef ROTT (3,4), Tomas LOKAJICEK (1)1: Institute of Geology of the Czech Academy of Sciences, Czech Republic; 2: Institute of Geophysics of the Czech Academy of Science, Czech Republic; 3: Faculty of Science, Charles University, Prague, Czech Republic; 4: Správa železnic, státní organizace, Czech RepublicMicro-fracturing in SCB test: Acoustic emission analysisMode I fracture toughness test was performed on the Cotta sandstone on semi-circular bend specimen in a symmetric geometry. The twenty-two channels were used for acoustic emission (AE) monitoring during the loading up to the failure. This study presents a detail AE analysis focused on the better understanding of micro-mechanisms leading to formation of fracture process zone (FPZ) and the following fracture propagation. The interpretation was based on the stress-induced changes in locations and source mechanisms of AEs. As a result, the micro-cracking can be divided into three following intervals: FPZ initiation, FPZ formation and fracture propagation. Each separate interval has its different AE characteristics that are presented in this paper. | Fracture process zone, Fracture propagation, Acoustic emission, Source mechanism, Moment tensor, Semi-circular bend test
T15: Rock and rock mass propertiesHerbert H. EINSTEINMassachusetts Institute of Technology, United States of AmericaPhysical Modeling in Rock Mechanics and Rock EngineeringThe paper is intended to pay homage to Professor Leopold Müller who was a leading developer and user of physical models. This will be done by reviewing physical models of fundamental material behavior, geologic mechanisms, and especially jointed rock. On this basis complex models of geologic processes and of structures on and in rock masses will be discussed. As will be shown this sequence of topics also corresponds to the history of physical models. Finally, critical aspects, namely the issues of scaling and of obsoleteness because of powerful simulation models will be addressed leading to the outlook as to where physical models can and should be used. | Physical Models, Material, Geology, Jointed Rock, Rock Structures
T15: Rock and rock mass propertiesTomas LOKAJICEK (1), Daniela RIMNACOVA (2), Richard PRIKRYL (3), Ali AMINZADEH (1), Matej PETRUZALEK (1)1: Institute of Geology of the Czech Academy of Sciences, Czech Republic; 2: Institute of Rock Structure and Mechanics, Academy of Sciences of the Czech Republic; 3: Faculty of Science, Charles University in Prague, Czech RepublicThermal degradation study of Westerly granite by ultrasonic sounding and mercury porosimetryWesterly granite (WG) is a well-known rock, believed to be isotropic. We studied WG samples heated between 100°C and 800°C, by ultrasonic sounding (US), mercury intrusion porosimetry (MIP). Thermal treatment studies are important for localities like nuclear waste storages, geothermal projects, rocks and earthquake mechanics. All measurements were done at room temperature. It was found that P and S US wave velocity, amplitude, frequency and elastic modulus decreased more than 60% as a result of thermal rock material disintegration due to the increased temperature treatment. Image analyses showed that there is also a preferred orientation of microcracks regardless of their size and thermal treatment level. MIP showed that the pore size distributions vary with different heating temperatures in depending on the thermal WG treatment. | Westerly granite, thermal treatment, ultrasonic sounding, mercury intrusion porosimetry
T15: Rock and rock mass propertiesDaniela ŘIMNÁČOVÁ (1), Dominik VÖRÖŠ (1), Vendula NATHEROVÁ (1,2), Richard PŘIKRYL (2), Tomáš LOKAJÍČEK (3)1: Institute of Rock Structure and Mechanics of the Czech Academy of Sciences, Czech Republic; 2: Institute of Geochemistry, Faculty of Science, Charles University in Prague, Czech Republic; 3: Institute of Geology of the Czech Academy of Sciences, Czech RepublicPorosity of source rocks eligible for interaction with gases and liquidsThe extent of the porosity of different source rocks may vary with their composition, weathering of the bedrock etc. To determine the further use of source rocks, it is necessary to understand and describe their physicochemical properties. Complex textural analyses of source rocks with variable amounts of organic matter were carried out using N2 and CO2 sorption, scanning electron microscopy and mercury intrusion porosimetry. The total adsorption of CO2 ranged from 0.03 to 1.5 mmol/g. The porosity and the pore size distribution varied according to the origin of the studied samples. The porosity ranged from 0.2% to 21%. Lower porosity values indicated a connection with gas capturing. Higher porosity values can be explained by the presence of macropores and larger pores, serving mainly for the migration of gases and liquids. Monitoring of sorption properties can provide a scientific basis for the safe utilization of reservoirs and rock layers. | Rocks, porosity, gas adsorption, textural parameters
T15: Rock and rock mass propertiesRahul Rooplal KATRE, Nikhil Ninad SIRDESAI, Sandeep PANCHALDepartment of Mining Engineering, Visvesvaraya National Institute of Technology, Nagpur, Maharashtra, IndiaInfluence of grain-size on damage in thermally treated granites- A Review and Novel quantification techniquesResponse of thermally treated granites are analyzed by several authors for processes like geothermal energy extraction, underground disposal nuclear waste, energy storage and structures exposed to fires. Although the conducted research helps to increase our understanding on the granites, quantification of thermal rock damage requires further studies which consequently alter the physico- mechanical response. So far, thermal damage is determined as a function of elastic modulus. However, an accurate determination of elastic modulus requires specialized laboratory facilities. When the treated granites (600°C) are allowed to cool in ambient temperature, the density decreases by 7.7%, 2.2% and 3.67% for coarse, medium and fine-grained granite, respectively. This reduction is primarily caused by the volumetric expansion of the mineral grains as seen by internal micro-cracking. In this study, the authors have quantified damage as a function of rock properties other than elastic modulus to appreciate the influence of temperature on varying grain-size. | Granite, Mineralogy, Morphology, Temperature, Damage
T15: Rock and rock mass propertiesAndreas MAYER (1), Franz REITER (2), Andreas FREUDENTHALER (3), Miroslav MARENCE (4)1: Büro für Geologie und Hydrogeologie ZT GMBH, Austria; 2: ÖBB Infrastruktur AG; 3: AFRY Austria GMBH; 4: AFRY Austria GMBHThe Tauernmoos pressure tunnel: a multidisciplinary approach to verify and ensure design rock mass conditions during constructionA 1.6 km long headrace tunnel has been constructed for the Tauernmoos hydro power plant. For the dimensioning of the tunnel lining, a minimum elastic modulus requirement of 15 GPa for the surrounding rock mass was formulated. The objective for the geological documentation was therefore the identification of zones with an elastic modulus below the required minimum. This was achieved by detailed mapping of the embrasure as well as by correlating the UCS, determined by Schmidt hammer, with the elastic modulus. For parts of the headrace tunnel, additional dynamic elastic moduli were established using refraction seismic surveying. That way, critical areas in terms of deformational behavior along the headrace tunnel could be determined. A consolidation grouting campaign with primary and secondary injection rings was carried out to improve the elastic moduli. The success of this measures was confirmed with a post-grouting seismic survey. | headrace tunnel, elastic modulus, Schmidt hammer, refraction seismic, grouting
T15: Rock and rock mass propertiesYulong SHAO, Jineon KIM, Jae-Joon SONGSeoul national university, Korea, Republic of (South Korea)4D imaging of crack evolution and failure mode in 3DP rock-like samples under uniaxial compression by using in-situ micro-ct technologyPrevious studies have investigated static cracks and pores before and after compressive tests of 3D-printed (3DP) rock with limitations in describing real-time cracking and damage evolution during compression. In this study, compression tests were conducted on 3DP gypsum rocks using an in-situ micro-computed tomography (micro-CT) system to obtain 2D CT images during compression. Through 3D reconstruction of 2D CT images, crack propagation and pore evolution of 3DP gypsum rocks could be illustrated from a 3D stereoscopic perspective and quantitatively analyzed. Results indicated that multiple tensile cracks propagated along the axial direction during compression. Initially, the volume of 3DP gypsum rocks decreased owing to pore closure during the compaction stage in which cracks were yet to be initiated. As the external stress exceeded the bearing capacity of 3DP gypsum rocks, the crack volume increased first marginally and then rapidly as cracks initiated and further developed with the increased stress. | 3DP gypsum rocks, in-situ micro-CT, 3D reconstruction, crack propagation, pore evolution
T15: Rock and rock mass propertiesMinoru SATO (1), Takato TAKEMURA (2), Daisuke ASAHINA (3)1: Central Research Institute of Electric Power Industry, Japan; 2: Geomechanics Lab., Department of Earth and Environmental Sciences, Nihon University; 3: Geological Survey of Japan, AISTMechanical properties of 3D printed sandstone analogue with different binder ratesThe mechanical properties of natural rocks obtained by laboratory tests vary considerably with rock anisotropy and heterogeneity by the formation process, and measurement accuracy of the equipment. However, it is difficult to evaluate these effects separately using natural rocks. Using three-dimensional (3D)-printed analogue minimizes the variations in the mechanical properties of rocks. In this study, the mechanical properties of 3D-printed sandstone analogues with different binder rates and jacketing conditions are examined at conventional triaxial compression (CTC) and true triaxial compression (TTC) stress conditions. This study demonstrates that the peak strength is slightly different for the same binder-sand weight rate samples; however, the deformation behavior observed from the shape of the stress–strain curve is similar. The mechanical properties and deformation behavior of the 3D-printed sandstone analogues are similar to those of natural sedimentary rocks under CTC and TTC testing conditions. | 3D printing, sandstone, mechanical properties, true triaxial test, triaxial test, P-wave velocity
T15: Rock and rock mass propertiesRupesh Kumar VERMA (1), Giang Dinh NGUYEN (2), Murat KARAKUS (2), Abbas TAHERI (3)1: Aurelia Metals, New South Wales, Australia.; 2: University of Adelaide, Adelaide, Australia; 3: Queen's University Kingston, Ontario, CanadaFull-field strain evolution in Brazilian Disc tests using Digital Image Correlation and Adelaide University Indirect Tensile strength test (AUSBIT)Strain energy storing and dissipation characteristics of rock govern the dynamics associated with its failure mode. Such failure, especially in indirect tensile strength tests occurs in a split second, which practically disables the efficient application of image-based instrumentations to obtain the full-field strain evolution during the fracturing process. This paper presents the application of our recently developed innovative experimental methodology, named Adelaide University Snapback Indirect Tensile Strength test (AUSBIT), to indirect tensile testing of strong and brittle rocks. AUSBIT enables control of the disc specimen's cracking process in indirect tensile strength tests and captures the complete class II (snapback) post-peak load-displacement response. These experiments, in conjunction with advanced instrumentations based on Digital Image Correlation (DIC), provide us with full-field strain distributions over the surface of disc specimen. The results obtained are promising, showing both snapback post-peak responses and the evolution of full-field strain distributions. | Brazilian disc, Digital Image Correlation, strain burst, strain energy storing, dissipation, tensile strength
T15: Rock and rock mass propertiesKatharina Meta NEUMANN, Mandy DUDA, Tobias BACKERSRuhr-University, Bochum, GermanyEffect of cyclic thermal loading on a carbonate rock: implications for thermal energy storageBecause renewable energy, such as wind and solar energy, is subject to temporal fluctuations, solutions are needed to store the energy in order to use it during periods of low energy production. Sensible thermal energy storage in rock (e.g. Alami et al. 2020) and seasonal geothermal energy storage are two options among some. The cyclic heating and cooling of the rock associated with cyclic storage can cause variations in the rock’s thermo-hydromechanical properties (Fränzer et al. 2023). To understand and specify those changes different rocks from a Jurassic carbonate rock formation in Southern Germany, a formation also targeted for geothermal use, was characterised before and after cyclic thermal loading. We investigated elastic, inelastic and thermal properties before and after thermal treatment to 100 °C and 800 °C. The results contribute to the understanding of thermally-induced changes in properties of rock and rock mass relevant for thermal energy storage. | thermal cycling, sensible heat thermal energy storage, limestone, carbonate rocks, thermal and mechanical properties
T15: Rock and rock mass propertiesMaría RAMÍREZ-BERASATEGUI (2), Diego-José GUERRERO-MIGUEL (1), Ramón GUTIÉRREZ-MOIZANT (2), María-Belén PRENDES-GERO (1), Martina-Inmaculada ÁLVAREZ-FERNÁNDEZ (1)1: DinRock Group. Universidad de Oviedo.; 2: Universidad Carlos III de MadridInfluence of shape surface on the actual stress distribution generated along the contact during the uniaxial compressive strength testUniaxial compressive strength is one of the key mechanical properties used to characterize rock materials. From international (ISRM) to national (ASTM, UNE) standards have been developed to ensure the trustfulness of testing results. However, they are quite severe with the geometrical tolerances considering the brittleness of rock materials, that provokes the specimens to form chips while machining them during the preparation process. This research analyses the influence of the surface geometrical deviations of the samples during the uniaxial compressive test. The effect of the stress distribution at the contact surface is analyzed using machined metal samples that accurately reproduce controlled flatness deviations. Moreover, pressure films are placed at the contact area to qualitatively record their influence on the actual contact stress distribution. These results are compared to those obtained on rock specimens. Therefore, influence of real contact conditions can be addressed according to the actual machining possibilities of rock materials. | uniaxial compressive strength, contact conditions, experimental contact pattern, load distribution
T15: Rock and rock mass propertiesMaximiliano R. VERGARA (1,2,3), Ana LIBREROS (4), Karl BALTHASAR (3)1: Skava consulting SA, Providencia, Chile; 2: Skava consulting ZT, Salzburg, Austria; 3: Institute of Soil Mechanics and Rock Mechanics, Karlsruhe Institute of Technology, Karlsruhe, Germany; 4: Ed. Züblin AG, Zentrale Technik - Tunnel Engineering, Stuttgart, GermanyExperimental and numerical study on the creep behavior of a rock mass with filled jointsThe time-dependent behavior of the rock mass is primarily controlled by the time-dependent deformation of the rock mass discontinuities. While most investigations concerning creep in rock masses have focused on the creep behavior of the intact rock, there is limited experimental data available on the creep behavior of rock fractures and discontinuities. In this study, direct shear creep tests were carried out on rough and saw-cut rock joints artificially filled with ground rock to investigate the creep behavior of rock fractures in the laboratory. The experimental results demonstrate that the creep deformation and failure potential in a filled joint depends on the shear-stress/shear-strength ratio, the magnitude of the shear stress, and filling thickness. Subsequently, the observed creep behavior of the rock joints was implemented into a numerical model to simulate the creep response of a jointed rock mass with varying fracture densities. | Rock joint creep, Rock mass creep, Joint shear creep test, Rock mass creep model
T15: Rock and rock mass propertiesLucas Conrad WITTE, Mandy DUDA, Murat AYDIN, Hossein ASGHARI CHEHREH, Tobias BACKERSRuhr-University Bochum, GermanyGeomechanical characterization of two granites to establish an experimentally based benchmark for numerical simulation – a laboratory studySince decades, numerical models have been used to predict the behavior of the subsurface in civil and geological engineering projects. The validity of these codes must be tested against field observations or, more often, apparently simple laboratory experiments, whose outcome is typically known to the modeler. Therefore, there is a distinct need for an objective procedure to verify if codes are capable to mirror and predict supposedly simple, physical processes. In this Study we have determined microstructural properties, geometric and grain densities, ultrasonic wave velocities, static moduli, uniaxial compressive strengths, tensile strengths, the time dependence of geomechanical properties, thermal and hydraulic properties. | Rock mechanics, rock mass properties, laboratory experiments, granite
T15: Rock and rock mass propertiesMaría Elvira GARRIDO (1), José B. SERÓN-GAÑEZ (1), Víctor MARTÍNEZ-IBÁÑEZ (1), Carlos HIDALGO-SIGNES (1), Roberto TOMÁS (2), Martina-Inmaculada ÁLVAREZ-FÉRNANDEZ (3)1: Universitat Politècnica de València, Spain; 2: Universidad de Alicante; 3: Universidad de OviedoPoint Load Strength Index of a limestone exposed to high temperatures and correlation with uniaxial compressive strengthThe most common procedure to obtain rock strength is the uniaxial compressive strength test (UCS). Extracting rock samples weakened by temperature can affect the estimation of the UCS values. Estimating UCS using the Point Load Test (PLT) is possible because both are linearly related. PLT needs smaller samples and is quicker and cheaper than the UCS test. This research determines UCS, Point Load Strength Index, and β-values (i.e., the ratio between UCS and Point Load Strength Index) of a limestone exposed to temperatures up to 900°C and then cooled on air or by immersion in water. Results show that strength and β-values decrease as temperature increases. There are two threshold temperatures in the relationship between point load strength and UCS in Pedra de Borriol samples: 600 ºC for samples subjected to slow cooling and 400 ºC for those subjected to quick cooling. | UCS, PLT, limestone, high temperatures, Pedra de Borriol
T15: Rock and rock mass propertiesRisto KIURU (1), Sophie HAAPALEHTO (2)1: Oy Rock Physics Finland Ltd, Finland; 2: Posiva Oy, FinlandModified transient plane source measurements of Olkiluoto migmatiteFinland is moving forward as the first country to solve the geological final disposal of spent nuclear fuel. Due to the temperature sensitive nature of the used disposal method, thermal design of the repository layout is necessary. This design process requires information of the thermal properties of the rock mass as confining parameters for modelling. As part of this process, modified transient plane source (MTPS) measurements of the thermal properties of Olkiluoto migmatite were carried out between 2019 and 2021. The MTPS method was used to measure simultaneously thermal conductivity and thermal effusivity. Additionally, density measurements were done, allowing the calculation of thermal diffusivity and specific heat capacity. The assumption of normally distributed data was tested using the Shapiro-Wilk test for normality and normal probability plots. Finally, the data were fitted with Gaussians using the maximum likelihood method. | geological disposal, thermal properties, thermal conductivity, thermal effusivity. modified transient plane source, MTPS
T15: Rock and rock mass propertiesVasileios KALLIMOGIANNIS (1), Charalampos SAROGLOU (1,2)1: National Technical University of Athens, Greece; 2: University of Leeds, UKMechanical properties of carbonate fault rocksThe tectonic processes that take place inside a fault zone change the initial structure of the parent rocks and impact their properties. In the present study, the mechanical properties of five (5) types of carbonate fault rocks from Lefkada Island, Greece, are investigated and compared to the corresponding properties of the parent carbonate rocks. Due to their tectonic disturbance and weak nature, the studied fault rocks are difficult to sample and test using the methodologies suggested by the international standards in Rock Mechanics (ISRM, ASTM). Therefore, a new methodology to sample and perform laboratory tests in such materials is used. The mechanical properties of each studied type presented a high variance which relates to the different structural and textural properties of the tested samples. Those properties were quantified to shed light on the factors that control the strength of the studied fault rocks. | Carbonate fault rocks, Mechanical properties, Structural properties, Textural properties, Sample preparation, Uniaxial Compressive Strength
T15: Rock and rock mass propertiesVasileios KALLIMOGIANNIS (1), Charalampos SAROGLOU (1,2)1: National Technical University of Athens, Greece; 2: University of Leeds, UKClassification of weak, carbonate fault rocksThe most common rock mass classification systems have been developed around hard rocks and do not fully apply to the characterization of weak rocks. Moreover, fault carbonate rocks present unique properties that cannot be accounted for when using these systems. Therefore, a new classification scheme is needed to accurately predict their mechanical properties. Weak, carbonate fault rocks from Lefkada island, Greece, are studied via a series of laboratory tests. Based on the geological background and our findings, the fault rocks are classified into four main types: Parent rocks, Welded breccias, Unwelded breccias and Matrix material. A methodology to estimate the Uniaxial Compressive Strength (UCSi) of each fault rock type is proposed. The results indicate that the Uniaxial Compressive Strength of the welded/unwelded breccias is a function of the corresponding strength of their components (fragments and matrix) and the matrix ratio (the percentage of matrix in a given volume). | Carbonate fault rocks, Mechanical properties, Structural properties, Textural properties, Sample preparation, Uniaxial Compressive Strength
T15: Rock and rock mass propertiesVíctor MARTÍNEZ-IBÁÑEZ (1), Carlos HIDALGO SIGNES (1), María Elvira GARRIDO (1), José Bernardo SERÓN GÁÑEZ (1), Roberto TOMÁS (2), Celestino GONZÁLEZ-NICIEZA (3)1: Universitat Politècnica de València, Spain; 2: Universidad de Alicante, Spain; 3: Universidad de Oviedo, SpainVariation in the drilling rate in thermally treated limestones through penetration-time curves from Sievers’ J-miniature drill testsIn this research we subject Prada limestone samples to temperatures of 600 ºC, and then we perform Sievers’ J-miniature drill tests to study the evolution of the penetration over time. We identify two characteristic intervals in the penetration–time plots: a superficial region with a variable penetration rate that includes an initial maximum value, and a deeper region in which the penetration rate stabilizes. Thermally treated samples exhibit an increase in the initial and final penetration rates, which indicates thermal damage both superficially and in-depth. We also observe that the time necessary to reach a stable drilling rate dramatically increases with temperature, involving an important part of the total test time. That has a clear influence on the final SJ value from Sievers’ J-miniature drill tests and is a starting point to determine a corrected SJ value for thermally treated limestones. | Rock drillability, Sievers’ J-miniature drill tests, SJ value, Thermal treatment, Temperature, Limestone
T15: Rock and rock mass propertiesSai Srujan Kumar CHALAVADI (1), Mahendra SINGH (1), Yogendra SINGH (1), Jaysing CHOUDHARI (2)1: Indian Institute of Technology Roorkee, Roorkee, India; 2: Fortescue Metals Group Ltd, East Perth, West AustraliaEffect of scale and in-situ stress ratio on the deformation modulus of rock mass around tunnelsAssessment of rock mass modulus is an essential part of analysis and design of tunnels. An in-house study was conducted to understand the variation of rock mass modulus around a tunnel to changing joint characteristics and far-field in-situ stress ratios. In each test, tunnel support pressures and displacements at the boundary of the test specimen were monitored. An exhaustive analysis of test results revealed that the deformation modulus is more sensitive to varying in-situ stress ratio than joint orientations. The modulus is found to decrease with increasing stress ratio. In addition to in-house study tests, analysis of the laboratory test results on jointed rock and small-scale rock mass specimens from literature proved a profound scale effect on deformation modulus. | Tunnels, Rock mass modulus, Joints, Joint factor, Scale effect
T15: Rock and rock mass propertiesLars JACOBSSON, Mathias FLANSBJER, Jörgen LARSSONRISE Research Institutes of Sweden AB, SwedenDirect shear tests on large natural and artificially induced rock fractures in a new laboratory equipmentA direct shear equipment for testing rock fractures up to 400×600 mm size, and up to 5 MN force in both normal and shear loading directions, was developed. Normal loading and direct shear tests under constant normal stiffness (CNS) and constant normal load (CNL) conditions were conducted on 300×500 mm specimens, one planar steel joint and two natural and two tensile induced rock fractures. Design targets, e.g. system to maintain undisturbed fractures up to testing and high system stiffnesses to achieve well-controlled shear tests, were verified by the experiments. A new optical system for local deformation measurements was used to accurately determine fracture displacements besides conventional non-local deformation measurements. The determined normal stiffnesses were similar previous results from the literature on smaller fractures, whereas the shear stiffness data are novel. The results provide a new insight into processes at the onset of fracture slip. | Rock fractures, large scale direct shear equipment, local optical deformation measurements, CNL, CNS, fracture stiffness
T15: Rock and rock mass propertiesDiego-José GUERRERO-MIGUEL (1), Martina-Inmaculada ÁLVAREZ-FERNÁNDEZ (1), María-Belén PRENDES-GERO (1,2), Celestino GONZÁLEZ-NICIEZA (1), Covadonga BETEGÓN-BIEMPICA (2), Emilio MARTÍNEZ-PAÑEDA (3)1: DinRock Group, University of Oviedo; 2: Construction and Manufacturing Engineering Department. University of Oviedo; 3: Department of Civil and Environmental Engineering, Imperial College LondonNew testing equipment to study dynamic fracture of rock and cement-based materials subjected to the action of roadheadersNew customized testing equipment specifically developed to address the dynamic fracture of material excavated by a roadheader at a laboratory scale is shown. Furthermore, limestone and cement-based material samples are tested to analyze the response of both the material and the cutting head when the number of acting picks is increased as a consequence of the translation of the whole roadheader during the excavation process. Results prove that the new equipment allows to identify the initial and end points of the contact between the sample and each of the picks, as well as the relation between the material strength and the mechanical specifications of the excavating machine. Thus, the new equipment can be used to tailor cutting head designs and to optimize the cutting parameters for a particular mechanical removal operation. | dynamic fracture, roadheader, excavation, rock cutting
T15: Rock and rock mass propertiesDimitrios KOTSANIS, Pavlos NOMIKOSNational Technical University of Athens, GreeceCorrelating uniaxial compression strength and static Young's modulus with Schmidt hardness for prasinitesThe scope of this study is to investigate the potential correlation of the Schmidt hammer rebound number with the uniaxial compressive strength and the static Young's modulus of prasinites, a metabasic petrological type outcropping in Attica Peninsula, Greece. Research works of similar content require the direct determination of the mechanical properties under consideration, so sixteen samples of NX diameter were prepared and examined in the laboratory. Then, the interpretation of the results revealed the relationship between the Schmidt hammer rebound hardness with the uniaxial compressive strength and the static Young's modulus of the studied rock materials. The derived empirical equations can provide valuable information for this rock type and can be used for preliminary investigations, at least in the study region. | Schmidt hardness, Uniaxial compressive strength, Static Young's modulus, Prasinites
T15: Rock and rock mass propertiesMaximiliano R. VERGARA (1,2,3)1: Skava consulting SA, Providencia, Chile; 2: Skava consulting ZT, Salzburg, Austria; 3: Institute of Soil Mechanics and Rock Mechanics (IBF), Karlsruhe Institute of Technology (KIT), Karlsruhe, GermanyComparison of conventional and cyclic oedometer swelling tests on rock specimensThe swelling behavior of rocks can be significantly affected by variations in moisture history, particularly through cyclic wetting and drying. The oedometer swelling test is widely utilized to assess the swelling characteristics of rock specimens. In this study, a comparison was made between conventional oedometer swelling tests and cyclic wetting and drying oedometer swelling tests on rock specimens. The objective was to evaluate the influence of cyclic wetting and drying on the resulting swelling curve. The slope of the swelling curve obtained from the cyclic test was more than double that of the conventional test. This comparison underscores the importance of accounting for cyclic wetting and drying conditions when assessing the swelling behavior of rocks and highlights the potential implications for long-term engineering projects involving rock structures. | Cyclic swelling, Rock swelling, Oedometer swelling test, Opalinus Clay
T15: Rock and rock mass propertiesEsteban HORMAZABAL, Andrea RUSSOSRK Consulting Chile, ChilePractical estimation of veinlets shear strength properties in hypogene rock massStructures present in rock masses have a significant importance on strength and deformation of the rock mass that govern the rock mass’ performance in underground mining. Although important progress has been made in these last decades, data on their geomechanical properties is still limited. Furthermore, the majority of studies on joints characterization are connected to rock slopes, open structures and / or with soft infilling material, and low confinement stress conditions; while in underground hypogene rock mass, minor structures are generally sealed, with fillings not necessarily categorized as soft, and variable magnitude and orientation of the major stresses defined by the mining excavations sequences. This paper presents a practical approach to estimate the veinlets shear strength properties on hypogene rock mass based on rock mechanics tests results and Barton Bandis criterion, corresponding mainly to sealed veinlets with fillings with higher strength than those usually found in open pit mining. | Veinlet’s strength properties, rock mass characterization, Barton Bandis criterion