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Experimental study on the effect of unloading rate on gneiss rockburst

Journal of Rock Mechanics and Geotechnical Engineering 2024年第6期16卷 2064-2076页

作者： Dongqiao Liu Jie Sun Ran Li Manchao He Binghao Cao Chongyuan Zhang Wen Meng State Key Laboratory for Tunnel Engineering China University of Mining and TechnologyBeijing100083China Key Laboratory of Active Tectonics and Geological Safety Ministry of Natural ResourcesInstitute of GeomechanicsChinese Academy of Geological SciencesBeijing100081China School of Mechanics and Civil Engineering China University of Mining and TechnologyBeijing100083China

Rockburst are often encountered in tunnel construction due to the complex geological *** study the influence of unloading rate on rockburst,gneiss rockburst experiments were conducted under three groups of unloading rates.A high-speed photography system and acoustic emission(AE)system were used to monitor the entire process of rockburst process in *** results show that the intensity of gneiss rockburst decreases with decrease of unloading rate,which is manifested as the reduction of AE energy and fragments ejection *** mechanisms are proposed to explain this effect:(i)The reduction of unloading rate changes the crack propagation mechanism in the process of *** makes the rockbursts change from the tensile failure mechanism at high unloading rate to the tension-shear mixed failure mechanism at low unloading rate,and more energy released in the form of shear crack ***,less strain energy is converted into kinetic energy of fragments ejection.(ii)Less plate cracking degree of gneiss has taken shape due to decrease of unloading rate,resulting in the destruction of rockburst incubation *** enlightenments of reducing the unloading rate for the project are also described *** rockburst magnitude is reduced from the medium magnitude at the unloading rate of 0.1 MPa/s to the slight magnitude at the unloading rate of 0.025 MPa/s,which was judged by the ejection velocity.

关键词： Rockburst unloading rate Crack propagation Influence mechanisms

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Effect of fatigue loading-confining stress unloading rate on marble mechanical behaviors: An insight into fracture evolution analyses

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Journal of Rock Mechanics and Geotechnical Engineering 2020年第6期12卷 1249-1262页

作者： Yu Wang Dongqiao Liu Jianqiang Han Changhong Li Hao Liu Beijing Key Laboratory of Urban Underground Space Engineering Department of Civil EngineeringSchool of Civil and Resource EngineeringUniversity of Science and Technology BeijingBeijing100083China State Key Laboratory for GeoMechanics and Deep Underground Engineering China University of Mining and TechnologyBeijing100083China Institute of Acoustics Chinese Academy of SciencesBeijing100190China

Rocks in underground works usually experience rather complex stress *** this,their fracture mechanism is significantly different from rocks subjected to conventional triaxial compression *** effects of stress disturbances on rock geomechanical behaviors under fatigue loading conditions and triaxial unloading conditions have been reported in previous ***,little is known about the dependence of the unloading rate on fatigue loading and confining stress unloading(FL-CSU)conditions that influence rock *** this paper,we aimed at investigating the fracture behaviors of marble under FL-CSU conditions using the post-test X-ray computed tomography(CT)scanning technique and the GCTS RTR 2000 rock mechanics *** show that damage accumulation at the fatigue stage can influence the final fracture behaviors of *** stored elastic energy for rock samples under FL-CSU tests is relatively larger compared to those under conventional triaxial tests,and the dissipated energy used to drive damage evolution and crack propagation is larger for FL-CSU *** FL-CSU tests,as the unloading rate increases,the dissipated energy grows and elastic energy *** scanning after the test reveals the impacts of the unloading rate on the crack pattern and a fracture degree index is therein defined in this context to represent the crack *** shows that the crack pattern after FL-CSU tests depends on the unloading rate,and the fracture degree is in agreement with the analysis of both the energy dissipation and the amount of energy *** effect of unloading rate on fracture evolution characteristics of marble is revealed by a series of FL-CSU tests.

关键词： Fatigue loading Confining stress unloading unloading rate Energy evolution Computed tomography(CT)scanning

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Deformation and damage properties of rock-like materials subjected to multi-level loading-unloading cycles

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Journal of Rock Mechanics and Geotechnical Engineering 2023年第7期15卷 1768-1776页

作者： Zhizhen Liu Ping Cao Qingxiong Zhao Rihong Cao Fei Wang Yellow River Laboratory Zhengzhou UniversityZhengzhou450001China School of Resource and Safety Engineering Central South UniversityChangsha410083China School of Engineering University of WarwickCoventryCV47ALUK

In the process of engineering construction such as tunnels and slopes,rock mass is frequently subjected to multiple levels of loading and unloading,while previous research ignores the impact of unloading rate on the stability of rock mass.A number of uniaxial multi-level cyclic loading-unloading experiments were conducted to better understand the effect of unloading rate on the deformation behavior,energy evolution,and damage properties of rock-like *** experimental results demonstrated that the unloading rate and relative cyclic number clearly influence the deformation behavior and energy evo-lution of rock-like *** particular,as the relative cyclic number rises,the total strain and reversible strain both increase linearly,while the total energy density,elastic energy density,and dissipated energy density all rise *** contrast,the irreversible strain first decreases quickly,then stabilizes,and finally rises *** the unloading rate increases,the total strain and reversible strain both increase,while the irreversible strain *** dissipated energy damage was examined in light of the aforementioned experimental *** accuracy of the proposed damage model,which takes into account the impact of the unloading rate and relative cyclic number,is then confirmed by examining the consistency between the model predicted and the experimental *** proposed damage model will make it easier to foresee how the multi-level loading-unloading cycles will affect the rock-like materials.

关键词： Incremental cyclic loading-unloading unloading rate Strain characteristics Energy evolution Damage model

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An approach to measure infill matric suction of irregular infilled rock joints under constant normal stiffness shearing

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Journal of Rock Mechanics and Geotechnical Engineering 2018年第4期10卷 653-660页

作者： Libin Gong Ana Heitor Buddhima Indraratna School of Civil Mining and Environmental Engineering University of Wollongong

Rock joints infilled with sediments can strongly influence the strength of rock mass. As infilled joints often exist under unsaturated condition, this study investigated the influence of matric suction of infill on the overall joint shear strength. A novel technique that allows direct measurement of matric suction of infill using high capacity tensiometers(HCTs) during direct shear of infilled joints under constant normal stiffness(CNS) is described. The CNS apparatus was modified to accommodate the HCT and the procedure is explained in detail. Joint specimens were simulated by gypsum plaster using threedimensional(3D) printed surface moulds, and filled with kaolin and sand mixture prepared at different water contents. Shear behaviours of both planar infilled joints and rough joints having joint roughness coefficients(JRCs) of 8-10 and 18-20 with the ratios of infill thickness to asperity height(t/a)equal to 0.5 were investigated. Matric suction shows predominantly unimodal behaviour during shearing of both planar and rough joints, which is closely associated with the variation of unloading rate and volumetric changes of the infill material. As expected, two-peak behaviour was observed for the rough joints and both peaks increased with the increase of infill matric suction. The results suggest that the contribution of matric suction of infill on the joint peak normalised shear stress is relatively independent of the joint roughness.

关键词： Infilled rock joints Matric suction High capacity tensiometer (HCT) Three-dimensional (3D) printing Normalised shear stress unloading rate

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Influence of excavation schemes on slope stability: A DEM study

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Journal of Mountain Science 2020年第6期17卷 1509-1522页

作者： WANG Zhen-yu GU Dong-ming ZHANG Wen-gang Key Laboratory of New Technology for Construction of Cities in Mountain Area Chongqing UniversityChongqing 400045China School of Civil Engineering Chongqing UniversityChongqing 400045China National Joint Engineering Research Center of Geohazards Prevention in the Reservoir Areas Chongqing UniversityChongqing 400045China

Slope failure due to improper excavation is one of common engineering disasters in *** explore the failure mechanism of soil slope induced by toe excavation,especially to investigate the influence of excavation unloading path and rate on slope stability,a numerical slope model was built via particle flow code PFC2 *** development of crack and strain during excavation were obtained and used to evaluate the deformation ***,excavation types representing different unloading paths and rates were compared in terms of crack number and strain *** indicate that crack number and strain level induced by horizontal column excavation are much greater than those of vertical column excavation and oblique *** crack number and strain level increase with excavation unloading ***,the feasibility of taking the average strain of slope surface and the average value of maximum strain along monitoring lines to represent the global deformation characteristics were *** study can provide a theoretical guidance for slope monitoring and preliminary optimal selection of excavation scheme in the design and construction of slope engineering.

关键词： Slope toe excavation unloading path unloading rate Strain distribution Slope stability Discrete element method

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