scholarly journals An Experimental Study on Cracking Behavior of Precracked Sandstone Specimens under Seepage Pressure

2018 ◽  
Vol 2018 ◽  
pp. 1-10 ◽  
Author(s):  
Qibin Lin ◽  
Ping Cao ◽  
Hua Wang ◽  
Rihong Cao
Keyword(s):  
Shear Failure ◽  
Fractured Rock ◽  
Axial Stress ◽  
Failure Process ◽  
Tensile Failure ◽  
Peak Strain ◽  
Compression Tests ◽  
Cracking Behavior ◽  
Seepage Pressure ◽  
Loading Device

This paper aims to investigate the strength and failure mechanism of fractured rock under seepage pressure. For this purpose, precracked sandstone specimens were prepared with different fissure angles, and a seepage pressure loading device was created. Together with the acoustic emission (AE) system, the loading device was adopted to perform uniaxial compression tests with or without seepage pressure. The main results are as follows. Combined with axial stress-strain curves, photographic monitoring results and the output of AE counts and rock failure process can be generally divided into four stages: microcrack closure, elastic deformation, crack growth and propagation, and final failure. The seepage pressure had a significant effect on the mechanical properties of the specimens: the specimens under seepage pressure lagged far behind those without seepage pressure in peak strength but maintained a comfortable lead in peak strain. Under seepage pressure, the typical failure features of the specimens varied with the fissure angles: the specimens with small fissure angles (i.e., [0°,30°]) mainly underwent tensile failure; those with medium fissure angles (i.e., [30°,60°]) suffered from shear failure; and those with large fissure angles (i.e., [60°,75°]) were prone to tensile-shear failure.

scholarly journals Experimental Study on Rock-Like Specimens with Single Flaw under Hydro-Mechanical Coupling

2019 ◽  
Vol 9 (16) ◽  
pp. 3234 ◽  
Author(s):  
Jinquan Xing ◽  
Cheng Zhao ◽  
Songbo Yu ◽  
Hiroshi Matsuda ◽  
Chuangchuang Ma
Keyword(s):  
Mechanical Properties ◽  
Shear Failure ◽  
Water Pressure ◽  
Triaxial Compression ◽  
Confining Pressure ◽  
Tensile Failure ◽  
Compression Tests ◽  
Cracking Behavior ◽  
Mechanical Coupling ◽  
High Confining Pressure

In order to study the mechanical characteristics and cracking behavior of jointed rock mass under hydro-mechanical coupling, a series of uniaxial compression tests and triaxial compression tests were carried out on cylinder gypsum specimens with a single pre-existing flaw. Under different confining pressures, water pressure was injected on the pre-existing flaw surface through a water injection channel. The geometrical morphology and tensile or shear properties of the cracks were determined by X-ray computed tomography (CT) and scanning electron microscope (SEM). Based on the macro and micro observation, nine types of cracks that caused the specimen failure are summarized. The results of mechanical properties and crack behavior showed that the confining pressure inhibited the tensile cracks, and shear failure occurred under high confining pressure. The water pressure facilitated the initiation and extension of tensile crack, which made the specimens prone to tensile failure. However, under the condition of high confining pressure and low water pressure, the lubrication effect had a significant effect on the failure pattern, under which the specimens were prone to shear failure. This experimental research on mechanical properties and cracking behavior under hydro-mechanical coupling is expected to increase its fundamental understanding.

scholarly journals Failure Process Simulation of Interlayered Rocks under Compression

2018 ◽  
Vol 2018 ◽  
pp. 1-13
Author(s):  
Chi Yao ◽  
Sizhi Zeng ◽  
Jianhua Yang
Keyword(s):  
Shear Failure ◽  
Failure Process ◽  
Strength Criterion ◽  
Tensile Failure ◽  
Strength Anisotropy ◽  
Rigid Block ◽  
Bedding Planes ◽  
Typical Experiment ◽  
Confining Pressures ◽  
Spring Method

Anisotropy in strength and deformation of rock mass induced by bedding planes and interlayered structures is a vital problem in rock mechanics and rock engineering. The modified rigid block spring method (RBSM), initially proposed for modeling of isotropic rock, is extended to study the failure process of interlayered rocks under compression with different confining pressures. The modified rigid block spring method is used to simulate the initiation and propagation of microcracks. The Mohr–Coulomb criterion is employed to determine shear failure events and the tensile strength criterion for tensile failure events. Rock materials are replaced by an assembly of Voronoi-based polygonal blocks. To explicitly simulate structural planes and for automatic mesh generation, a multistep point insertion procedure is proposed. A typical experiment on interlayered rocks in literature is simulated using the proposed model. Effects of the orientation of bedding planes with regard to the loading direction on the failure mechanism and strength anisotropy are emphasized. Results indicate that the modified RBSM model succeeds in capturing main failure mechanisms and strength anisotropy induced by interlayered structures and different confining pressures.

scholarly journals Experiment and Failure Analysis of Rock-Like Material Affected by Different Excavation Depths

2021 ◽  
Vol 2021 ◽  
pp. 1-15
Author(s):  
Yuan Tian ◽  
Zhende Zhu ◽  
Xinyu Liu ◽  
Yanxin He
Keyword(s):  
Axial Stress ◽  
Peak Stress ◽  
Initial Crack ◽  
Peak Strain ◽  
Compression Tests ◽  
Hole Depth ◽  
Single Hole ◽  
Stress Direction ◽  
Secondary Cracks ◽  
Shaped Crack

In order to increase the understanding of the strength and failure mechanism of rock mass during tunnel excavation, a series of uniaxial compression tests were conducted on mortar specimen with cracks and holes by using a rock mechanics servo-controlled testing system. And by monitoring the experimental process, the initiation, propagation, and coalescence process of cracks were observed and characterized. According to the experimental results, the influences of the excavation depth on the mechanical parameters and fracture characteristics of mortar specimens with single hole and the ones with single-hole crack were analyzed in detail. In the specimens with single hole, the peak strength decreases with the increase of hole depth, but the peak strain and elastic modulus have no obvious linear correlation with the hole depth. And the position and angle of initial crack change differently with the increase of the hole depth. The position of initial crack moves from the side of the hole to the top of the hole. When the hole depth exceeds 50%, the crack initiation angle is no longer inclined to the axial stress direction, but parallel to the axial stress direction. In the specimens with single prefabricated crack, the wing-shaped secondary cracks are generated at the tip of the precrack, and the antiwing-shaped secondary cracks are generated at the tip when approaching the peak stress. However, in the specimens with single-hole crack, no antiwing-shaped crack appears. And when the hole depth reaches 80%, two wing-shaped cracks appear at the precrack tip. One of the new wing-shaped cracks appears in the direction of the extension line of the precrack.

Pore Properties as Indicators of Deterioration Mechanisms in Slightly Weathered Tuffs

2019 ◽  
Author(s):  
Yufang Tan ◽  
Lihui Li ◽  
Xiaolong Deng ◽  
Beixiu Huang
Keyword(s):  
Pore Structure ◽  
Shear Failure ◽  
Tensile Failure ◽  
Compression Tests ◽  
Chemical Parameters ◽  
Pore Throat ◽  
Magnetic Resonance Technique ◽  
Deterioration Mechanism ◽  
Pore Properties ◽  
Rock Mechanical Behavior

The mineralogy and chemistry of tuff rocks are variable and heterogeneous due to volcanic activity and hydrothermal alteration, in addition to weathering, which makes it difficult to explain the deterioration mechanisms of the weathered rocks based merely on mineralogical and chemical parameters. Studies of tuff weathering indicate that subtle weathering can modify pore structure and subsequently affect the rock mechanical behavior, suggesting that quantitative pore structure parameters are important indicators of the tuff deterioration mechanism. We identified the pore size distribution of pore bodies and pore throats of both slightly weathered tuffs and fresh tuffs using nuclear magnetic resonance technique and mercury intrusion porosimetry. Meso-level uniaxial compression tests were conducted on the tuff samples under a stereomicroscope using MTI-LMs (miniature tensile instrument-light microscopes) to obtain information regarding crack propagation and the deformation process. A comparison of pore properties of slightly weathered tuffs and fresh tuffs indicates that the introduction of additional mesopores (10–50 nm) and pore throat expansion occurs during weathering. The result of mechanical experiments reveal that alteration of the pore structure influences the tuff failure mode. Slightly weathered tuffs show shear failure as cracks initiate in the altered minerals or matrix, while the fresh tuffs exhibit tensile failure as cracks initiate in the intact and fresh minerals and matrix. Based on the results presented here, it is considerable to regard tuff pore properties as potential indicators of the micro-mechanism of substantial macro-deterioration due to weathering.

scholarly journals Numerical Studies on the Failure Process of Heterogeneous Rock Material with Preexisting Fracture under Uniaxial Compression

2018 ◽  
Vol 2018 ◽  
pp. 1-12 ◽  
Author(s):  
Qi Zhang ◽  
Dan Ma ◽  
Jiangfeng Liu ◽  
Kai Zhang ◽  
Zhiqiang Fan
Keyword(s):  
Shear Failure ◽  
Failure Process ◽  
Damage Model ◽  
Rock Material ◽  
Tensile Failure ◽  
Underground Engineering ◽  
Intact Specimen ◽  
Numerical Studies ◽  
Heterogeneous Rock ◽  
Reduced Parameters

It is of vital importance to understand the failure processes of the heterogeneous rock material with different kinds of preexisting fractures in underground engineering. A damage model was introduced to describe the initiation and propagation behaviors of the fractures in rock. Reduced parameters were applied in this work because the microcracks in the rock were neglected. Then, the numerical model was validated through comparing the simulation results with the laboratory observations. Finally, a number of numerical uniaxial compressive tests were performed on heterogeneous rock specimens with preexisting fracture, and the influence of the heterogeneity of the rock and the angle and length of the preexisting fractures was fully discussed. The results showed that the brittleness of the rock increased with the increase of the homogeneity index, and tensile failure was the main failure form for relatively heterogeneous rock, whilst shear failure was the main failure form for relatively homogeneous rock. The uniaxial compressive strengths of the specimens with the angles of 0, 30, 45, and 60 of the preexisting fracture dropped 62.7%, 54.7%, 46.6%, and 38.2% compared with that of the intact specimen; the tensile cracks were more difficult to form, and the required load was increasing with the increase of the angle of the preexisting fracture; besides, antiwing cracks were difficult to form than wing cracks because the tensile stress in wing cracks’ area was greater than that in antiwing cracks’ area. The uniaxial compressive strengths of the specimens with the lengths of 20 mm, 25 mm, 30 mm, and 35 mm of preexisting fracture dropped 38.6%, 46.6%, 53.4%, and 56.6% compared with that of the intact specimen, and the damage conditions of the samples with different lengths of preexisting fracture were similar.

scholarly journals Study on stability of filling wall under lateral large-span composite hinge fracture of hard critical block

2021 ◽  
Vol 104 (2) ◽  
pp. 003685042110216
Author(s):  
Chenghai Li ◽  
Yajie Liu ◽  
Jianbiao Bai ◽  
Qing Ge
Keyword(s):  
Field Test ◽  
Shear Failure ◽  
Lateral Displacement ◽  
Axial Stress ◽  
Tensile Failure ◽  
Shear Cracks ◽  
Large Span ◽  
The Stability ◽  
Number Of Segments ◽  
Hinge Fracture

There is still a lack of mature researches on the stability mechanism, influencing factors and control technology of the gob-side filling wall, and systematic researches on the cracking forms and characteristics of the stope roof and the stability of the filling wall are rather insufficient. This paper is aimed at investigating the deformation law of the filling wall under the large-span composite hinge fracture of the hard critical block and solving the difficulty that the large-span critical block lateral fracture poses to gob-side entry retaining. Research methods such as theoretical calculation, mechanical analysis, numerical simulation and field test were adopted comprehensively in this study. When the large-span critical block B is divided into two or three parts, its force on the immediate roof decreases with the increase in the number of segments. Meanwhile, as the number of segments grows, the displacement and axial stress of the filling wall both decrease gradually; the tensile failure weakens relatively, while the shear failure changes slightly. Moreover, both the number of shear cracks and the number of tensile cracks in the filling wall are positively correlated with the strain. When the critical block divided into four parts, the amount of lateral displacement is about 190 mm, and the axial displacement reaches the minimum (about 235 mm). The stability of the filling wall along the gob-side entry is closely related to the lateral fracture span of the stope roof. Under the lateral fracture of the hard critical block, a smaller span of the lateral fracture of the critical block corresponds to a smaller force on the filling wall and a weaker damage to the filling wall. The field test result verifies that cleaving the large-span critical block into smaller segments is conducive to reducing surrounding rock and filling wall deformation.

scholarly journals Experimental Investigation on Failure Modes and Mechanical Properties of Rock-Like Specimens with a Grout-Infilled Flaw under Triaxial Compression

2019 ◽  
Vol 2019 ◽  
pp. 1-14
Author(s):  
Huilin Le ◽  
Shaorui Sun ◽  
Feng Zhu ◽  
Haotian Fan
Keyword(s):  
Mechanical Properties ◽  
Rock Mass ◽  
Epoxy Resin ◽  
Failure Modes ◽  
Shear Failure ◽  
Fractured Rock ◽  
Triaxial Compression ◽  
Friction Angle ◽  
Confining Pressure ◽  
Compression Tests

Flaws existing in rock mass are one of the main factors resulting in the instability of rock mass. Epoxy resin is often used to reinforce fractured rock mass. However, few researches focused on mechanical properties of the specimens with a resin-infilled flaw under triaxial compression. Therefore, in this research, epoxy resin was selected as the grouting material, and triaxial compression tests were conducted on the rock-like specimens with a grout-infilled flaw having different geometries. This study draws some new conclusions. The high confining pressure suppresses the generation of tensile cracks, and the failure mode changes from tensile-shear failure to shear failure as the confining pressure increases. Grouting with epoxy resin leads to the improvement of peak strengths of the specimens under triaxial compression. The reinforcement effect of epoxy resin is better for the specimens having a large flaw length and those under a relatively low confining pressure. Grouting with epoxy resin reduces the internal friction angle of the samples but improves their cohesion. This research may provide some useful insights for understanding the mechanical behaviors of grouted rock masses.

scholarly journals Dynamic Tensile Strength of Dry and Saturated Hard Coal under Impact Loading

Energies ◽  
2020 ◽  
Vol 13 (5) ◽  
pp. 1273
Author(s):  
Xianlei Zhu ◽  
Qing Li ◽  
Guihua Wei ◽  
Shizheng Fang
Keyword(s):  
Tensile Strength ◽  
High Speed ◽  
Shear Failure ◽  
Split Hopkinson Pressure Bar ◽  
Failure Process ◽  
Tensile Failure ◽  
Hard Coal ◽  
Control Group ◽  
Hopkinson Pressure Bar ◽  
Brazilian Disk

To evaluate the influence of water content on the hard coal dynamic behavior, the dynamic tensile properties of saturated coal Brazilian disk (BD) samples were studied using a split Hopkinson pressure bar system, and dry samples were also tested as a control group. In the range of impact speeds studied, the tensile strength of the saturated coal is lower than that of the dry specimen. A synchronized triggering high-speed camera was used to monitor the deformation and failure process of dry and saturated coal samples, allowing analysis of the failure stages and mechanism of dynamic BD test, the broken mode was classified into three types, which can be classified into unilateral tensile failure, bilateral or multilateral tensile failure, and shear failure. Finally, fragments smaller than 5 mm in diameter were statistically analyzed. There is less debris in range of 0–5.0 mm for the saturated coal sample than for the dry coal. This study provides some information about the dynamic response of the hard coal for the relevant practical engineering.

scholarly journals Effects of Kaolin Addition on Mechanical Properties for Cemented Coal Gangue-Fly Ash Backfill under Uniaxial Loading

Energies ◽  
2021 ◽  
Vol 14 (12) ◽  
pp. 3693
Author(s):  
Faxin Li ◽  
Dawei Yin ◽  
Chun Zhu ◽  
Feng Wang ◽  
Ning Jiang ◽  
...  
Keyword(s):  
Mechanical Properties ◽  
Compressive Strength ◽  
Elastic Modulus ◽  
Fly Ash ◽  
Uniaxial Compressive Strength ◽  
Shear Failure ◽  
Coal Gangue ◽  
Tensile Failure ◽  
Peak Strain ◽  
Local Shear

In this investigation, six groups of cemented coal gangue-fly ash backfill (CGFB) samples with varying amounts of kaolin (0, 10, 20, 30, 40, and 50%) instead of cement are prepared, and their mechanical properties are analyzed using uniaxial compression, acoustic emission, scanning electron microscopy, X-ray diffraction, and Fourier transform infrared spectroscopy. The uniaxial compressive strength, peak strain, and elastic modulus of CGFB samples decreased with the kaolin content. The average uniaxial compressive strength, elastic modulus, and peak strain of CGFB samples with 10% amount of kaolin are close to that of CGFB samples with no kaolin. The contribution of kaolin hydration to the strength of CGFB sample is lower than that of cement hydration, and the hydration products such as ettringite and calcium-silicate-hydrate gel decrease, thereby reducing strength, which mainly plays a role in filling pores. The contents of kaolin affect the failure characteristics of CGFB samples, which show tensile failure accompanied by local shear failure, and the failure degree increases with the kaolin content. The porosity of the fracture surface shows a decreasing trend as a whole. When the amount of kaolin instead of cement is 10%, the mechanical properties of CGFB samples are slightly different from those of CGFB samples without kaolin, and CGFB can meet the demand of filling strength. The research results provide a theoretical basis for the application of kaolin admixture in fill mining.

scholarly journals A Study of the Relationship between the Stress State and Failure Mode of Concrete Specimens

2018 ◽  
Vol 2018 ◽  
pp. 1-6
Author(s):  
Xinyu Liang ◽  
Faning Dang
Keyword(s):  
Internal Stress ◽  
Failure Mode ◽  
Shear Failure ◽  
Ambient Pressure ◽  
Failure Process ◽  
Failure Surface ◽  
The State ◽  
Tensile Failure ◽  
Aspect Ratios ◽  
The Relationship

An investigation of concrete specimen’s strength and its changing mechanism based on numerical simulation of the failure process of axis-stressed concrete specimens with different aspect ratios was described. The state of internal stress and growth of crack of axis-stressed concrete specimens, as well as the changing mechanism of specimen strength under different ambient pressure values, were investigated. The results revealed that specimen strength and failure surface decreased as the aspect ratio is increased. The specimen strength is dependent on the state of internal stress and decreased with decreasing ambient pressure. Additionally, the failure mode shifted from shear failure to tensile failure gradually.

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