ISRM 2023 - PUBLICATIONS

T12: New developments in rock supportManuel ENTFELLNER, Helmut WANNENMACHERImplenia Österreich GmbH, AustriaNew yielding elements made of high-strength expanded polystyrene (HS-EPS)Yielding elements as a part of the shotcrete lining represent state-of-the-art tunnelling in overstressed weak ground conditions. These elements avoid overstressing of the shotcrete lining during the early curing process, where the displacement rates are highest and the shotcrete strength/stiffness lowest. A novel yielding element of High-Strength Expanded Polystyrene (HS-EPS) is introduced, which overcomes existing systems’ drawbacks. This innovative system is lightweight and allows for rapid installation. Furthermore, the modular setup of the element permits an easy on-site adaption to react to in-situ deformation patterns and changing ground conditions. Recent experiences from applications in alpine base tunnels in overstressed weak ground conditions are presented. | Tunnelling, Yielding Principle, Overstressed Weak Ground, Squeezing Ground, Yielding Elements, HS-EPS
T12: New developments in rock supportIryna KOVALEVSKA, Volodymyr BONDARENKO, Hennadii SYMANOVYCH, Ivan SHEKA, Yevhenii TSIVKADnipro University of Technology, UkraineModeling the rational parameters for innovative fastening systems in mine workings using composite materialsThe leading methodologies (mathematical modeling and computational experiment) for studying geomechanical models to represent the state of systems "rock mass - reinforced rocks - innovative support system" in complex mining and geological conditions are considered. Mathematical modeling of carbon fiber-reinforced plastic arch support (CFRP) was carried out. A comparative analysis of the stress and strain state of the system "rock mass - support made of composite materials" with the stress and strain state of the existing roof support system in the mine was carried out. A laboratory simulation was carried out to determine the carrying capacity of the new shoring structure by creating a model on a 3D-printer in accordance with the basic principles of geometric similarity theory. The reliability of the calculations carried out and the results obtained has been substantiated by comparing the data of the computational experiment and the laboratory simulation. | carbon fiber-reinforced plastic, mine workings, composite material, support, stress-strain state, physical and mechanical properties
T12: New developments in rock supportYasuhiro YOKOTA (1,2), Kensuke DATE (1,2), Atsushi SAINOKI (3), Masako ISHII (2,4), Kazuhiko MASUMOTO (2,4), Mori UTSUNO (2)1: KAJIMA Technical Research Institute Singapore, Singapore; 2: KAJIMA Corporation, Japan; 3: Kumamoto University; 4: Kajima Technical Research Institute, JapanReinforcement effect of deformation-controlled tunnelling supports based on three-dimensional tunnel excavation analysisIn recent years, many tunnel excavation projects are planned despite swelling ground conditions and/or great depths subjected to high ground pressure around the world. In such cases, there is a risk that the high ground pressure will exceed the loading capacity of the conventional rigid supports, leading to brittle failure. Accordingly, the authors have been developing new deformation-controlled supports that can reduce stress acting on steel supports, shotcrete, and rock bolts by gradually resisting high ground pressure while controlling tunnel deformation. Here, we report on a study of support specifications suitable for actual tunnel excavation, performed by developing the constitutive model of deformation-controlled supports and analyzing 3D tunnel excavation. | Tunnel, simulation, deformation-controlled support, steel support, shotcrete, rock bolt
T12: New developments in rock supportRoberto LUIS (1), Rico BRÄNDLE (1), Gabriel VON RICKENBACH (1), German FISCHER (2), Sergio MARK (2)1: Geobrugg AG; 2: Geobrugg Andina SpARational design for tunnel ground support with membranes based on the geomechanically classification of Q by BartonThe parameters to consider for an optimal solution for the design of underground rock support are the lifetime of the tunnels, the use of the tunnels, the safety level, and the cost. One of these design systems was developed by Barton. Nevertheless, the system has some limitations when it comes to dynamic ground conditions or higher static loads. With new ground support high-tensile steel membranes, the focus shifts from the bolt only, to an underground rock retention system where the membrane plays a significant role. An optimal load transfer from rock mass to the support system, be it dynamic or static, can be reached by high tensile steel meshes, that allow a wider bolt spacing. The proposed extension of the Q System considers the severe conditions the mining industry faces to get the ore from increasingly deep stops. | Q System, rock support, ground conditions, ground support membranes, tunnel safety, high tensile steel membrane
T12: New developments in rock supportBjarte GRINDHEIM (1), Charlie Chunlin LI (1), Are Håvard HØIEN (2)1: Norwegian University of Science and Technology (NTNU), Trondheim, Norway; 2: Norwegian Public Roads Administration (NPRA), Bergen, NorwayFull-Scale Pullout Tests of Rock Anchors in Limestone Testing the Interfacial Bond StrengthsRock anchors are used to stabilise large scale infrastructures. The literature describes four failure modes of rock anchors: (1) steel tensile failure; (2) anchor-grout interface failure; (3) grout-rock interface failure; and (4) rock mass uplift. In this study full scale field tests of rock anchors were performed in a limestone quarry. These tests were designed to test failure mode 2 and 3 with bar anchors, with and without an endplate. The tests of failure mode 2 showed that the shear stress on the anchor-grout interface is highest at the proximal and attenuates towards the distal end at small loads and it becomes approximately uniform at 50% of the ultimate pullout load. The anchors designed to test failure mode 3 had an endplate, they showed that the shear stress on the grout-rock interface was highest at the distal end above the endplate and attenuated upward before slip starts on the interface. | Rock anchor, load transfer, shear stress distribution, bond shear strength, field tests
T12: New developments in rock supportHonghao CHEN (1), Hamed Lamei RAMAND (1), Imrana KABIR (1), Onder KIMYON (1), Ren CHEN (1), Naresh KUMAR (1), Cindy GUNAWAN (3), Peter CRAIG (2), Ismet CANBULAT (1), Micheal MANEFIELD (1), Serkan SAYDAM (1)1: University of New South Wales, Australia; 2: Jennmar Australia; 3: University of Technology SydneyPrevention of catastrophic corrosion failure of rockbolt and cable bolt in underground coal minesThe catastrophic corrosion failures of rockbolts and cable bolts in underground coal mines have been reported from several mines in the past few decades. Many of the failed bolts have been in service for a short period. The preliminary studies have found that the failures occur by hydrogen-induced stress corrosion cracking (HISCC) and microbial-induced corrosion (MIC). In these types of failures, the local environment where the bolt was installed is the key to initiating and accelerating the corrosion process. This study investigates the capabilities of polymer coating and galvanising technologies for preventing bolt corrosion failures. We use our previously developed HISCC and MIC reproduction method to reproduce the corrosive environment in the lab. The laboratory study shows the benefit of polymer barrier coating compared to galvanising in an extreme environment, and it also has good resistance to MIC. | Ground support safety, corrosion, rockbolt, cable bolt, stress corrosion cracking, microbiological induced corrosion
T12: New developments in rock supportConrad BOLEY (1), Paul PRATTER (2), Lisa WILFING (2)1: Institute for Soil Mechanics and Geotechnical Engineering, Bundeswehr University Munich, Germany; 2: Boley Geotechnik GmbH, Munich, GermanyResearch of safety-relevant natural and structural factors influencing the load-bearing capacity of rock stabilization with chemical groutsGeotechnical structures are subject to environmental and structural factors depending on formation water or the rock fracture degree. These factors inevitably affect the load-bearing capacity of the structure and in consequence the stability. Due to increasingly dense development, space constraints and the relocation of buildings to the underground, the subsoil improvement is playing an increasingly important role, as this often means that the subsoil has to adapt to the necessary requirements of the structure and not vice versa. The research focuses on the stabilization of rock with different high performance chemical grouts. For this purpose, the rock mechanical testing program on grouted rock was extended by special tests to investigate the material behavior of the chemical grout and its bonding with the surrounding rock in detail. The results of the research work are of safety-relevant importance and should therefore already be considered in the design phase of a construction project. | Rock stabilization, chemical grout, formation water, rock fracture
T12: New developments in rock supportMathias LAURAEUS (1,3), Mikael RINNE (1), Antti LAUKKANEN (2)1: Department of Civil Engineering, Aalto University, Espoo, Finland; 2: Betulium Ltd, Espoo, Finland; 3: Sweco Finland Ltd, Helsinki, FinlandMicrofibrillated cellulose as additive for wet-mix shotcreteShotcrete is a widely used rock reinforcement method that significantly impacts the carbon footprint of underground construction and mining. The sustainability of shotcrete can be improved by, e.g., replacing a portion of cement in the mix with low-carbon materials or minimizing shotcrete rebound by increasing the plastic yield stress of fresh shotcrete. A microfibrillated cellulose (MFC) has recently drawn interest from the shotcrete industry due to its potential for improving the sustainability and cost-efficiency of shotcrete. The MFC is low-carbon footprint material that has rheology-modifying effects on aqueous systems, such as shear thinning behavior and high zero-shear viscosity. In this study, a preliminary investigation of the benefits of MFC in shotcrete application was done through a series of laboratory tests. Results indicate that the MFC improves the immediate stiffness of accelerated shotcrete, and other essential performance factors are not significantly affected. | Microfibrillated cellulose, shotcrete, additives, carbon footprint, rebound
T12: New developments in rock supportFei ZHAO, Zhenming SHI, Songbo YUDepartment of Geotechnical Engineering, College of Civil Engineering, Tongji University, Shanghai, People's Republic of ChinaResearch on application of new combined support structures in reinforcing rocky slopes containing weak interlayersAnti-sliding piles have good reinforcement effect in slope under earthquake. In this study, new combined piles are proposed, and models of bedding rocky slopes with different weak interlayers are established. The force characteristics, reinforcement mechanism and effect of the combined piles are analyzed. The main findings are as follows: the different mechanical mechanisms of the slope reinforced by the flexible and rigid combination of piles result in different deformation patterns; through the pre-stress of the horizontal connection structure, the h-shaped flexible structure connecting the double-row piles can reasonably distribute the squeezing pressure and shear force on the piles to realize the synergistic seismic resistance of the piles, and its reinforcement effect is better than other piles. Based on the above findings, the study of combined piles for reinforcing rocky slopes has important engineering significance. | Rocky slope with weak interlayers, New combined anti-slide piles, Reinforcement mechanisms and effects, Earthquake
T12: New developments in rock supportDanqi LICurtin University, AustraliaAn analytical model for cable bolts considering crack propagation in groutUnderstanding the mechanical behaviour of cable bolts under axial loading from analytical perspective is essential and economic for selecting the most appropriate cable bolt for a specific scenario and also the ground support system design. This study develops a novel analytical model coupling the crack propagation in the grout annulus to capture the load-displacement performance of cable bolts under axial loading. The majority of the input parameters associated with mechanic properties of the cable bolt and grout are readily determinable by laboratory tests. At the end, the capability of the proposed model to simulate the performance of cable bolts under axial loading is demonstrated by validating against experimental results in the literature. | Analytical model, Cable bolts, Pull out test; Crack propagation
T12: New developments in rock supportFrederick KUHNOWGEI ConsultantsBlast Induced Vibrations and Strain Rate Effects in Dynamic Capacity of Underground Concrete StructuresWhen performing blasting operations in open pit mines, large amounts of energy is released and transmitted through the rock. The energy released can have significant impacts on mining operations and can adversely affect the mine production. This technical paper presents recommendations for blast design to prevent damage from blasting on underground concrete structures. Emphasis is placed in vibrations generated by blasting and its effects are studied referring to an existing hard rock mine expansion and asks whether production blasting would damage adjacent underground concrete structures due to blast stress waves. A set of criteria was developed to implement when blasting near-by underground structures. Knowledge of particle velocity and wave propagation theory for site-specific conditions to determine a safe level of vibration was recommended. The results suggest that an increase in structural capacity (dynamic capacity) is expected when structures are subjected to loads at very high strain rates, such as those of blasts. | Blasting loads, wave propagation velocity, peak particle velocity, earthquake loads, dynamic capacity, underground structures
T12: New developments in rock supportDorna EMAMI (1), Souvik SAHA (2), Mehdi SERATI (1), Harry ASCHE (3), David J WILLIAMS (1)1: The University of Queensland, Australia; 2: University of Queensland – IIT Delhi Academy of Research, New Delhi, India; 3: Aurecon, Brisbane, AustraliaOn The Expected Location of Fire-Induced Concrete SpallingThe occurrence of fire-induced spalling in concrete structures and shotcrete elements (aka sprayed concrete) is influenced by various factors including the type of heat and applied fire curves, temperature gradient, sample size, and quality and mixture of the concrete. Predicting the location of spalling can significantly assist with developing fire resistance tests to allow for the correct placement of instrumentation and monitoring equipment such as temperature and pressure sensors, high-speed cameras, and 3D/2D Digital Image Correlation imaging, among others, in optimal positions to be able to closely monitor the spalling process. This study examines the data from tests previously carried out to generate a model for predicting the location of fire-induced spalling in concrete samples, and then compares it experimentally to validate the proposed model. The results indicate good compatibility between the data from literature and the performed experiments. | Fire-induced Spalling, Spalling Positions, Pressure, Temperature
T12: New developments in rock supportKunze LI, Hamed LAMEI RAMANDI, Chengguo ZHANG, Sahand TADBIRI, Serkan SAYDAM, Joung OHUniversity of New South Wales, Sydney, AustraliaInfluence of rock crystal structure on bond strength at the rock-shotcrete interfaceThe bond strength at the aggregate-cement paste interface is affected by the microstructure of the interfacial transition zone (ITZ). However, the influence of substrate crystal structure on the rock-shotcrete interface behaviour has received limited attention. This study investigates the impact of substrate crystal structure on the bonding strength of the rock-shotcrete interface. Gabbros and basalts used in this study have similar mineral compositions but have different grain sizes due to different cooling rates. Applying plain shotcrete to substrate samples to study the interface behaviours. Direct pull-off tests are conducted to investigate the bond strength at the interface after 28-day curing. The failed surfaces are examined using scanning electron microscopy imaging technique to further analyse the failure interface. The results indicate that hydration products can cover and embed into the rock surface. Basalt with fine-grained texture achieves denser ITZ than coarse-grained gabbro and results in stronger bond between rock and shotcrete. | Basalt, Gabbro, Rock-shotcrete interface, Bond strength, Crystal structure
T12: New developments in rock supportAna Carolina BAÊSSO (1), Euripedes do Amaral VARGAS JR. (1), Raquel Quadros VELLOSO (1), Eduardo Gomes MARQUES (2)1: Pontifical Catholic University of Rio de Janeiro, Brazil; 2: Federal University of ViçosaDetermination of tensile strength of rocks by CTC (compression-tensile load converter test)In order to obtain the direct tensile strength of the rocks by means of a device that is inexpensive and easy to use in a rock mechanics laboratory, a compression load converter was designed and manufactured in the PUC-Rio laboratory. This apparatus was named as a compression-tensile load converter (CTC), and was developed by Klanphumusri (2010). The equipment design allows the user to switch between tensile stress and compression applications on the same specimen during placement in the conventional compression machine. The apparatus was designed to test dog bone or halter rock samples with end diameter ranging from 75 to 100 mm. Seven specimens of syenogranites from Cachoeiro de Itapemirim, ES - Brazil were tested for equipment validation and the results were compared to those obtained in fifteen Brazilian tests. The direct tensile strength using the CTC showed consistent results, with lower strength than those obtained by the indirect method. | Direct tensile test; Tensile strength of rocks; Load converter, Geomechanical Properties
T12: New developments in rock supportJemishkumar Vijaykumar MODI (1,2), Debasis DEB (2), Rakesh KUMAR (2)1: Government Engineering College Palanpur; 2: Indian Institute of Technology KharagpurExperimental Investigations of Instrumented Fully Grouted Rock Bolts under Pull LoadRebar-type rock bolts of 22 mm and a length of 600 mm are instrumented with four resistance strain gauges along the length. A total of 450 mm bolt lengths is embedded with resin grouted inside a cement mortar cast cylindrical sample of diameter 250 mm. Strain gauges are placed on the surface of the rod at four locations. The diameter of the hole is varied as 32 mm, 36 mm, and 42 mm. The bolt is embedded cement mortar samples are placed in a pull-testing machine and firmly fixed on the frame by tie-rods. The rod is pulled with three different loading groups of rates. This paper analyzes load-deformation relationship curves for different hole diameters of pulling to observe the variation in peak bond strength and stiffness. The tensile strains obtained at four locations are validated with an analytical equation are in the paper. | Fully grouted rock-bolt, pull-out tests, bond strength, bond stiffness, axial strain
T12: New developments in rock supportGünther M. VOLKMANNDSI Underground Austria GmbH, AustriaVerification of design relevant parameters for new pipe umbrella support systemsSince the 90s pipe umbrellas have been used regularly to support tunnel headings in difficult ground conditions. During this time, the rules for design have continuously improved, but there are still problems to determine the equivalence of alternatively offered, new systems. For this reason, common connection types for pipe umbrella support systems are described and their characteristic design parameters, their advantages and disadvantages reviewed. Two different design approaches will be introduced and discussed. Different connection types or staggered connections / joints are assessed regarding their influence on the load-bearing capacity. The results of laboratory tests are discussed, and the necessity of a statistical evaluation shown. Having these results presented in a laboratory test report or a certificate issued by the producer in hand, it is possible to define for an owners representative whether alternative connection types are adequate or not. | pipe umbrella, canopy tube, design approach, connection types, laboratory bending tests