scholarly journals Triaxial Loading and Unloading Tests on Dry and Saturated Sandstone Specimens

2019 ◽  
Vol 9 (8) ◽  
pp. 1689 ◽  
Author(s):  
Diyuan Li ◽  
Zhi Sun ◽  
Quanqi Zhu ◽  
Kang Peng
Keyword(s):  
Triaxial Compression ◽  
Failure Process ◽  
Failure Behavior ◽  
Compression Tests ◽  
Loading Test ◽  
Rock Engineering ◽  
Sandstone Rock ◽  
Water Conditions ◽  
Deep Rock ◽  
Loading And Unloading

The brittle failure of hard rock due to the excavation unloading in deep rock engineering often causes serious problems in mining and tunneling engineering, and the failure process is always affected by groundwater. In order to investigate the effects of stress paths and water conditions on the mechanical properties and failure behavior of rocks, a series of triaxial compression tests were conducted on dry and saturated sandstones under various loading and unloading paths. It was found that when the sandstone rock samples are saturated by water, the cohesion, the internal friction angle and the Young’s modulus will decrease but the Poisson′s ratio will increase. The fracturing characteristics of the sandstone specimens are related to the initial confining pressure, the stress paths and the water conditions from both macroscopic and microscopic viewpoints. The failure of sandstone in unloading test is more severe than that under loading test, particularly for dry sandstone samples. In unloading test, the energy is mainly consumed for the circumferential deformation and converted into kinetic energy for the rock bursts. The sandstone is more prone to produce internal cracks under the effect of water, and the absorbed energy mainly contributes to the damage of rock. It indicates that the possibility of rockburst in saturated rock is lower than the samples in dry condition. It is important to mention that water injection in rock is an effective way to prevent rockburst in deep rock engineering.

scholarly journals Experimental Investigation on the Energy Properties and Failure Process of Thermal Shock Treated Sandstone Subjected to Coupled Dynamic and Static Loads

Minerals ◽  
2021 ◽  
Vol 12 (1) ◽  
pp. 25
Author(s):  
Xiang Li ◽  
Si Huang ◽  
Tubing Yin ◽  
Xibing Li ◽  
Kang Peng ◽  
...  
Keyword(s):  
Thermal Shock ◽  
Split Hopkinson Pressure Bar ◽  
Failure Process ◽  
Air Cooling ◽  
Hopkinson Pressure Bar ◽  
Loading Test ◽  
Rock Engineering ◽  
Deep Rock ◽  
Pressure Bar ◽  
Cooling Air

Thermal shock (TS) is known as the process where fractures are generated when rocks go through sudden temperature changes. In the field of deep rock engineering, the rock mass can be subjected to the TS process in various circumstances. To study the influence of TS on the mechanical behaviors of rock, sandstone specimens are heated at different high temperatures and three cooling methods (stove cooling, air cooling, and freezer cooling) are adopted to provide different cooling rates. The coupled dynamic and static loading tests are performed on the heated sandstone through a modified split Hopkinson pressure bar (SHPB) system. The influence of heating level and cooling rate on the dynamic compressive strength, energy dissipations, and fracturing characteristics is investigated based on the experimental data. The development of the microcracks of the sandstone specimens after the experiment is analyzed utilizing a scanning electron microscope (SEM). The extent of the development of the microcracks serves to explain the variation pattern of the mechanical responses and energy dissipations of the specimens obtained from the loading test. The findings of this study are valuable for practices in rock engineering involving high temperature and fast cooling.

Constitutive model to simulate full deformation and failure process for rocks considering initial compression and residual strength behaviors

2019 ◽  
Vol 56 (5) ◽  
pp. 649-661 ◽  
Author(s):  
Wengui Cao ◽  
Xin Tan ◽  
Chao Zhang ◽  
Min He
Keyword(s):  
Constitutive Model ◽  
Residual Strength ◽  
Triaxial Compression ◽  
Failure Process ◽  
Deformation Model ◽  
Good Prediction ◽  
Compression Tests ◽  
Deformation And Failure ◽  
Macroscopic Deformation ◽  
Triaxial Compression Tests

A constitutive model with capacity to simulate the full deformation and failure process for rocks considering initial compression and residual strength behaviors is discussed in this paper. The rock was assumed to consist of the initial voids portion and the solid skeleton portion. The full deformation model of rocks can be established by the consideration of the macroscopic deformation of rocks and the microscopic deformations of the two different portions based on the statistical damage theory. Comparisons between the experimental data from triaxial compression tests and calculated results show that the proposed constitutive model provided a good prediction of the full deformation and failure process, including the effects of initial void compression, stiffness degradation, strain hardening–softening, and residual strength.

scholarly journals Experimental Study on the Permeability of Weakly Cemented Rock under Different Stress States in Triaxial Compression Tests

Geofluids ◽  
2018 ◽  
Vol 2018 ◽  
pp. 1-9 ◽  
Author(s):  
Gangwei Fan ◽  
Mingwei Chen ◽  
Dongsheng Zhang ◽  
Zhen Wang ◽  
Shizhong Zhang ◽  
...  
Keyword(s):  
Underground Mining ◽  
Axial Strain ◽  
Triaxial Compression ◽  
Confining Pressure ◽  
Initial Permeability ◽  
Compression Tests ◽  
Mining Operations ◽  
Stress Strain ◽  
Loading And Unloading ◽  
Stress States

Mudstone and shaly coarse sandstone samples of Jurassic units in northwestern China were collected to study the seepage mechanism of weakly cemented rock affected by underground mining operations. Samples were studied using seepage experiments under triaxial compression considering two processes: complete stress-strain and postpeak loading and unloading. The results show that permeability variations closely correspond to deviatoric stress-axial strain during the process of complete stress-strain. The initial permeability is 7 times its minimum, contrasting with lesser differentials of initial, peak, and residual permeability. The magnitude of permeability ranges from 10−17 to 10−19 m2, representing a stable water-resisting property, and is 1 to 2 orders lower in mudstone than that in shaly coarse sandstone, indicating that the water-resisting property of the mudstone is much better than that of the shaly coarse sandstone. Permeability is negatively correlated with the confining pressure. In response to this pressure, the permeability change in mudstone is faster than that in shaly coarse sandstone during the process of postpeak loading and unloading. Weakly cemented rock has lower permeability according to the comparison with congeneric ordinary rocks. This distinction is more remarkable in terms of the initial permeability. Analyses based on scanning electron microscope (SEM) observations and mineral composition indicate that the samples are rich in clay minerals such as montmorillonite and kaolin, whose inherent properties of hydroexpansiveness and hydrosliming can be considered the dominant factors contributing to the seepage properties of weakly cemented rock with low permeability.

Experimental Research of Fine Sandstone Strength and Deformation Characteristics under Different Confining and Hydraulic Pressure

2013 ◽  
Vol 353-356 ◽  
pp. 562-570 ◽  
Author(s):  
Zai Bin Liu
Keyword(s):  
Rock Strength ◽  
Pore Water Pressure ◽  
Water Pressure ◽  
Triaxial Compression ◽  
Confining Pressure ◽  
Hydraulic Pressure ◽  
Compression Tests ◽  
Exponential Relationship ◽  
Sandstone Rock ◽  
Strength And Deformation

In order to study sandstone rock strength and deformation parameters under pore water pressure conditions, triaxial compression tests of different hydraulic pressure were executed. Fitting equations of fine sandstone confining pressure and hydraulic pressure coupling effects were established. This research show that fine sandstone rock strength increases with confining pressure increases. Rock mass strength and cohesion have negative exponential relationship with hydraulic pressure. When the hydraulic pressure is 3MPa, elasticity and confining pressure fit to logarithmic relationship. Fine sandstone Elasticity modulus decreases with hydraulic pressure increases. Poisson’s ration and hydraulic pressure fit to linear relationship.

Research on Rock Burst Loading Test and PFC3D Numerical Simulation

2011 ◽  
Vol 243-249 ◽  
pp. 3012-3020 ◽  
Author(s):  
Yu Zhou ◽  
Shun Chuan Wu ◽  
Qing Liang Wu ◽  
Yu Tao Ma ◽  
Yong Tao Gao
Keyword(s):  
Laboratory Test ◽  
Rock Burst ◽  
Failure Process ◽  
Simulation Method ◽  
Exposed Surface ◽  
Loading Test ◽  
Tunnel Excavation ◽  
Burst Test ◽  
Maximal Load ◽  
Deep Rock

During the tunnel excavation in Zhang-Shi Expressway 2nd-Stage Project, rock burst phenomenon has occurred. Limy dolomite obtained from tunnel rock burst area is used to conduct laboratory loading rock burst test with simulation system of deep rock burst. Simultaneously, based on Particle Flow Theory and PFC3D program, a load-unload code is developed by fish language embedded in PFC3D to carry out simulation of laboratory loading rock burst test. Laboratory test result shows that the rock burst type and intensity of specimen are lagged and severe, respectively; During the test process, a spot of particles eject from the exposed surface; Obvious slabbing phenomenon can be seen on the exposed surface and the separate face of rock slab is parallel to the direction of maximal load σ1 as consistent with the actual phenomenon of engineering rock burst. In the loading rock burst simulation, the load grade, stress-step curve and failure mode of rock burst are almost consistent with the laboratory test. This simulation method describes the failure process actually and subtly, and reveals that the specimen fracture mechanism of loading rock burst is tensile type. Finally, some differences between loading and unloading tests of rock burst are discussed.

scholarly journals Stress Drop as a Result of Splitting, Brittle and Transitional Faulting of Rock Samples in Uniaxial and Triaxial Compression Tests

2015 ◽  
Vol 37 (1) ◽  
pp. 17-23 ◽  
Author(s):  
Jerzy Cieślik
Keyword(s):  
Stress Drop ◽  
Rock Sample ◽  
Triaxial Compression ◽  
Failure Process ◽  
Strength Loss ◽  
Axial Stiffness ◽  
Compression Tests ◽  
Rock Samples ◽  
Test Pressure ◽  
Triaxial Compression Tests

Abstract Rock samples can behave brittle, transitional or ductile depending on test pressure, rate of loading and temperature. Axial stiffness and its changes, relative and absolute dilatancy, yield, and fracture thresholds, residual strength are strongly pressure dependent. In this paper the stress drop as an effect of rock sample strength loss due to failure was analyzed. Uniaxial and triaxial experiments on three types of rock were performed to investigate the stress drop phenomenon. The paper first introduces short background on rock behavior and parameters defining a failure process under uniaxial and triaxial loading conditions. Stress drop data collected with experiments are analyzed and its pressure dependence phenomenon is described. Two methods for evaluation of stress drop value are presented.

Investigate the softening properties of weak interlayers in slope failure process using nanoindentation test and simulation

2020 ◽  
Author(s):  
Jingjing Xu ◽  
Yufei Feng ◽  
Xuhai Tang
Keyword(s):  
Slope Failure ◽  
Water Immersion ◽  
Triaxial Compression ◽  
Failure Process ◽  
Friction Angle ◽  
Gaussian Mixture ◽  
Nanoindentation Test ◽  
Compression Tests ◽  
Saturation Time ◽  
Rock Fragments

<p>This work proposed an available approach to analyze the property evolution of weak interlayers during immersion softening at micro and macro scales, which combining the advantages of nanoindentation tests and numerical modelling. The weak interlayers has significant impact on the failure process of natural slopes, however, their properties are difficult to be obtained using traditional triaxial compression tests. Because these weak interlayers are consist of clay and rock fragments which leads to the difficult to prepare intact samples. Additionally, the softening properties of these weak interlayers are strongly related to their fillings at micro scale. In this work, the weak interlayers is investigated using nano-scale micromechanical tests and upscaling methodologies, so only small rock fragments are required (see Fig.1). <br>In northwestern Hubei China, the mountains often developed several layers of weak interlayers with major lithology as shale which is sedimentary rock with low strength and dense clay particles. We investigated these shale fragments in weak interlayers, which is prone to decrease in strength induced by precipitation erosion. The Gaussian mixture model was used to analyze a large amount of data obtained by statistical grid nanoindentation method. Then the Mori-Tanaka scheme was used to homogenize the elastic properties of the samples and upscale the nanoindentation data to the macroscale. The hardness values which obtain by Berkovich and Cube corner indenter were able to assess the cohesion and friction angle of shale. Finally, these achieved parameters were applied in numerical model, in order to analyze the slope failure caused by the softening of weak interlayers (see Fig. 2).<br>The results show that: (1) the chlorite and muscovite minerals, which are major proportion of shale, soften or dissolve with the increasing saturation time. The fine mineral particles are gradually stripped from micro structure. As a result, at microscale the compact shale samples sale became loose. The strength of these shale samples are also decrease because water seeped through pores and micro cracks. (2) After water immersion, the friction angle is almost constant, while the elastic modulus and cohesion decrease significantly with increasing saturation time. (3) The shear strength decrease so that the shearing creep occurs along the weak interlayers surface, then bottom sliding surface is cut, which leads to landslide.</p>

scholarly journals Failure Behavior and Constitutive Model of Weakly Consolidated Soft Rock

2013 ◽  
Vol 2013 ◽  
pp. 1-8 ◽  
Author(s):  
Wei-ming Wang ◽  
Zeng-hui Zhao ◽  
Yong-ji Wang ◽  
Xin Gao
Keyword(s):  
Constitutive Model ◽  
Failure Mechanism ◽  
Triaxial Compression ◽  
Soft Rock ◽  
Confining Pressure ◽  
Western China ◽  
Failure Behavior ◽  
Correction Coefficient ◽  
Compression Tests ◽  
Mining Areas

Mining areas in western China are mainly located in soft rock strata with poor bearing capacity. In order to make the deformation failure mechanism and strength behavior of weakly consolidated soft mudstone and coal rock hosted in Ili No. 4 mine of Xinjiang area clear, some uniaxial and triaxial compression tests were carried out according to the samples of rocks gathered in the studied area, respectively. Meanwhile, a damage constitutive model which considered the initial damage was established by introducing a damage variable and a correction coefficient. A linearization process method was introduced according to the characteristics of the fitting curve and experimental data. The results showed that samples under different moisture contents and confining pressures presented completely different failure mechanism. The given model could accurately describe the elastic and plastic yield characteristics as well as the strain softening behavior of collected samples at postpeak stage. Moreover, the model could precisely reflect the relationship between the elastic modulus and confining pressure at prepeak stage.

scholarly journals An Analysis of the Mechanical Characteristics and Constitutive Relation of Cemented Mercury Slag

2017 ◽  
Vol 2017 ◽  
pp. 1-14
Author(s):  
Xinwei Li ◽  
Sui Zhang ◽  
E-chuan Yan ◽  
Duoyou Shu ◽  
Yangbing Cao ◽  
...  
Keyword(s):  
Triaxial Compression ◽  
Failure Process ◽  
Guizhou Province ◽  
Coarse Grained ◽  
Uniaxial Compression Test ◽  
Compression Tests ◽  
Slag Structure ◽  
Triaxial Compression Tests ◽  
Chang Model ◽  
Coarse Grained Soil

This study focuses on mercury slag in the Tongren area of Guizhou Province, China. Computed tomography (CT) is used with uniaxial and triaxial compression tests to examine the mechanical changes in cemented mercury slag and its formation. The CT results for the uniaxial compression test reveal the overall failure process of the mercury slag structure. Based on the coarse-grained soil triaxial test, a modified Duncan-Chang model is compared with the actual monitoring results and is found to be suitable for the analysis of the slag constitutive model.

scholarly journals Experimental and Numerical Study of Strength and Failure Behavior of Precracked Marble under True Triaxial Compression

2021 ◽  
Vol 2021 ◽  
pp. 1-11
Author(s):  
Yong Han ◽  
Yuemao Zhao ◽  
Jinglong Li
Keyword(s):  
Shear Failure ◽  
Numerical Study ◽  
Triaxial Compression ◽  
Numerical Results ◽  
Peak Strength ◽  
Failure Behavior ◽  
Compression Tests ◽  
True Triaxial ◽  
Fracturing Process ◽  
True Triaxial Compression

Cracks play an important role in evaluating the strength and failure behavior of engineering rock mass. In order to increase the understanding of strength and failure mechanism of precracked rock, crack propagation and coalescence from preexisting cracks under true triaxial compression are investigated using true triaxial compression tests and Cellular Automata Software for engineering Rockmass fracturing process (CASRock). Three types of specimens were studied experimentally and numerically. Experimental and numerical results show that both the preferential angle and areal intensity of preexisting cracks can affect the compressive strength and failure behavior of the specimens. The peak strength firstly decreases and then increases with increase of the preferential angle. Also, the peak strength nonlinearly decreases with the increase of cracks’ areal intensity. The numerical results show that the crack initiation and coalescence are observed and characterized from the inner and outer tips of preexisting cracks in specimens containing single crack and multiple parallel cracks. The main shear failure in the specimen containing multiple unparallel preexisting cracks initiate and propagate from one of the macroscopic preexisting cracks, and other preexisting cracks do not initiate, propagate, and coalesce until reaching the peak strength.

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