Study on Failure of Rock Mass around Deep Tunnel

2011 ◽  
Vol 99-100 ◽  
pp. 370-374 ◽  
Author(s):  
Yue Hong Qian ◽  
Ting Ting Cheng ◽  
Xiang Ming Cao ◽  
Chun Ming Song
Keyword(s):  
Rock Mass ◽  
Stress Field ◽  
Failure Modes ◽  
Shear Failure ◽  
Simple Function ◽  
Tensile Failure ◽  
Deep Tunnel ◽  
Main Mode

During excavating the problem of unloading is a dynamic one essentially. Assuming the unloading ruled by a simple function and based on the Hamilton principal, the distribution of the stress field nearby the tunnel is obtained. The characteristics of the failure nearby the tunnel are analyzed considering the shear failure and tensile failure. The results show that the main mode of the shear failure, intact and tensile failure occurs from the tunnel. The characteristic of the shear failure, intact and tensile failure are one of the likely failure modes.

scholarly journals Failure Characteristics and Mechanism of Multiface Slopes under Earthquake Load Based on PFC Method

2021 ◽  
Vol 2021 ◽  
pp. 1-11
Author(s):  
Tao Yang ◽  
Yunkang Rao ◽  
Huailin Chen ◽  
Bing Yang ◽  
Jiangrong Hou ◽  
...  
Keyword(s):  
Moisture Content ◽  
Failure Mechanism ◽  
Failure Modes ◽  
Shear Failure ◽  
Shaking Table ◽  
Tensile Failure ◽  
Particle Flow Code ◽  
Shear Cracks ◽  
Local Shear ◽  
Shear Slip

Understanding the failure mechanism and failure modes of multiface slopes in the Wenchuan earthquake can provide a scientific guideline for the slope seismic design. In this paper, the two-dimensional particle flow code (PFC2D) and shaking table tests are used to study the failure mechanism of multiface slopes. The results show that the failure modes of slopes with different moisture content are different under seismic loads. The failure modes of slopes with the moisture content of 5%, 8%, and 12% are shattering-shallow slip, tension-shear slip, and shattering-collapse slip, respectively. The failure mechanism of slopes with different water content is different. In the initial stage of vibration, the slope with 5% moisture content produces tensile cracks on the upper surface of the slope; local shear slip occurs at the foot of the slope and develops rapidly; however, a tensile failure finally occurs. In the slope with 8% moisture content, local shear cracks first develop and then are connected into the slip plane, leading to the formation of the unstable slope. A fracture network first forms in the slope with 12% moisture content under the shear action; uneven dislocation then occurs in the slope during vibration; the whole instability failure finally occurs. In the case of low moisture content, the tensile crack plays a leading role in the failure of the slope. But the influence of shear failure becomes greater with the increase of the moisture content.

Tensile behaviors of co-woven-knitted fabric reinforced composites under various strain rates

2011 ◽  
Vol 45 (24) ◽  
pp. 2495-2506 ◽  
Author(s):  
Pibo Ma ◽  
Hong Hu ◽  
Lvtao Zhu ◽  
Baozhong Sun ◽  
Bohong Gu
Keyword(s):  
Strain Rate ◽  
Failure Modes ◽  
Shear Failure ◽  
High Strain ◽  
Tensile Failure ◽  
Knitted Fabric ◽  
Strain Rates ◽  
High Strain Rates ◽  
Textile Composite ◽  
Interface Failure

This article reports the tensile behaviors of a novel kind of 3D textile composite, named as co-woven-knitted fabric (CWKF) reinforced composite, under quasi-static and high strain rates. The tensile tests were conducted along the warp direction (0°), bias direction (45°), and weft direction (90°) at quasi-static strain rate of 0.001/s and high strain rates ranging from 1589/s to 2586/s. The results indicate that the tensile strength, failure strain, tensile stiffness, energy absorption, and resilient energy are strain rate sensitive along all the three directions. The relationships between the mechanical parameters and the strain rate were also analyzed. The fractograph of the CWKF composite demonstrate that the tensile failure modes are matrix shear failure and fibers breakage under the quasi-static testing condition while interface failure and fibers pullout are at high strain rates.

scholarly journals Cracking Behaviors and Mechanical Properties of Rock-Like Specimens with Two Unparallel Flaws under Conventional Triaxial Compression

2019 ◽  
Vol 2019 ◽  
pp. 1-15 ◽  
Author(s):  
Huilin Le ◽  
Shaorui Sun ◽  
Chenghua Xu ◽  
Liuyang Li ◽  
Yong Liu
Keyword(s):  
Mechanical Properties ◽  
Inclination Angle ◽  
Failure Modes ◽  
Shear Failure ◽  
Triaxial Compression ◽  
Confining Pressure ◽  
Critical Value ◽  
Tensile Failure ◽  
Rock Bridge ◽  
Bridge Length

Flaws existing in rock masses are generally unparallel and under three-dimensional stress; however, the mechanical and cracking behaviors of the specimens with two unparallel flaws under triaxial compression have been rarely studied. Therefore, this study conducted comprehensive research on the cracking and coalescence behavior and mechanical properties of specimens with two unparallel flaws under triaxial compression. Triaxial compressive tests were conducted under different confining pressures on rock-like specimens with two preexisting flaws but varying flaw geometries (with respect to the inclination angle of the two unparallel flaws, rock bridge length, and rock bridge inclination angle). Six crack types and eleven coalescence types in the bridge region were observed, and three types of failure modes (tensile failure, shear failure, and tensile-shear failure) were observed in experiments. Test results show that bridge length and bridge inclination angle have an effect on the coalescence pattern, but the influence of bridge inclination angle is larger than that of the bridge length. When the confining pressure is low, coalescence patterns and failure modes of the specimens are greatly affected by flaw geometry, but when confining pressure rose to a certain level, the influence of confining pressure is larger than the effect of flaw geometry. The peak strength of the specimens is affected by flaw geometry and confining pressure. There is a critical value for the bridge length. If the bridge length is larger than the critical value, peak strengths of the samples almost keep constant as the bridge length increases. In addition, as the bridge inclination angle increases, there is an increase in the probability of tensile cracks occurring, and with an increase in the confining pressure, the probability of the occurrence of shear cracks increases.

EARTHQUAKE-INDUCED TOPPLING FAILURE MECHANISM AND ITS EVALUATION METHOD OF SLOPE IN DISCONTINUOUS ROCK MASS

2012 ◽  
Vol 04 (03) ◽  
pp. 1250036 ◽  
Author(s):  
AILAN CHE ◽  
XIURUN GE
Keyword(s):  
Rock Mass ◽  
Evaluation Method ◽  
Shear Failure ◽  
Central China ◽  
Tensile Failure ◽  
Seismic Stability ◽  
Great Earthquake ◽  
Inertia Force ◽  
Rock Slopes ◽  
Toppling Failure

The seismic behavior of rock slopes accompanied with discontinuity is heavily governed by the geometrical distribution and mechanical properties of discontinuity. Especially, high and steep rock slopes, which are dominated by sub-vertical discontinuity, are likely to collapse due to toppling failure and it causes serious damage to structures surrounding the slopes. Ten thousands of landslides, collapses and other geological disasters occurred in the Wenchuan Ms 8.0 great earthquake on May 12, 2008 in Sichuan province of central China. The field survey during the disaster investigations indicated that it shows the tensile failure close to the top of slop and the shear failure below it. However, it is difficult to assess quantitatively toppling failure potential. In order to clarify mechanism of toppling failure in rock slopes and evaluation on seismic stability, 2D joint elements around each rock column is proposed to simulate the discontinuity of rock slope, which is different from Goodman joint and composed with normal spring Kn and shear spring Ks without volume. By a nonlinear numerical FEM analysis, the dynamic response of the rock slopes could demonstrate the landslide mechanism. Coupled with the effect of amplification on the toppling, the seismic horizontal acceleration at the top of slopes is often large, and then coursed inertia force would far exceed the tensile strength of rock mass. Eventually, the opening and sliding of joint elements occurs on the slope are identified based on the nonlinear characteristics of the joint elements. The result shows that a toppling failure could have occurred on the slope and the sliding plane also could be observed, which shows agreement with the existing investigation flexural toppling failure during the Wenchuan great earthquake.

Study on Mechanism of Slope Instability with Weak Interlayer

2011 ◽  
Vol 71-78 ◽  
pp. 3615-3618 ◽  
Author(s):  
Yun Fei Wang ◽  
Fu Ping Zhong ◽  
Huai Bao Chu ◽  
Li Ping Wang
Keyword(s):  
Stress Field ◽  
Failure Mechanism ◽  
Shear Failure ◽  
Slope Instability ◽  
Tensile Failure ◽  
Cyclic Process ◽  
Research Subject ◽  
Geological Conditions ◽  
Weak Interlayer ◽  
Mass Rock

In the process of the highway building, especially in mountain region the some complex geological conditions often appears. In this paper, using the slope of highway with weak interlayer as the research subject, systematically analyzing the stress field and plastic field during the excavation of the slope, obtained the failure mechanism of the slope with weak interlayer, which is a cyclic process that weak interlayer shear failure led to the tensile failure of its upper mass rock. It has extraordinarily important guiding significance for the protection and reinforcement of similar slope.

scholarly journals Effect of Filling Interval Time on Long-Term Mechanical Strength of Layered Cemented Tailing Backfill

2016 ◽  
Vol 2016 ◽  
pp. 1-7 ◽  
Author(s):  
Shuai Cao ◽  
Wei-dong Song
Keyword(s):  
Compressive Strength ◽  
Mechanical Strength ◽  
Failure Modes ◽  
Shear Failure ◽  
Development Stage ◽  
Stability Control ◽  
Tensile Failure ◽  
Uniaxial Compression Test ◽  
Linear Elastic ◽  
Shear Mixing

To explore the influence that filling interval has on the mechanical strength of layered cemented tailing backfill (LCTB), uniaxial compression test is conducted on LCTB samples with a concentration of 70%, 72%, and 75% and a filling interval of 12 h, 24 h, 36 h, and 48 h. From the tests above, mechanical properties and failure modes of LCTB are acquired. The results are as follows: (1) The peak compressive strength of LCTB decreases as the filling interval increases, and it increases when the concentration grows with a certain length of filling interval. At the same time, the peak compressive strength and filling interval show polynomial distribution. (2) There are four stages during the loading process of cemented backfill specimen, that is, compression stage, linear elastic stage, crack extension stage, and undermines development stage. As the filling interval increases, CTB shows a failure mode of tensile failure-tensile shear failure transition-tensile and shear mixing destruction, which provides a theoretical basis for strength design and stability control of backfill.

scholarly journals Experimental Study of the Mechanical Characteristics of a Rock-Like Material Containing a Preexisting Fissure under Loading and Unloading Triaxial Compression

2020 ◽  
Vol 2020 ◽  
pp. 1-12 ◽  
Author(s):  
Taoli Xiao ◽  
Mei Huang ◽  
Min Gao
Keyword(s):  
Experimental Study ◽  
Failure Mode ◽  
Mechanical Characteristics ◽  
Failure Modes ◽  
Shear Failure ◽  
Triaxial Compression ◽  
Tensile Failure ◽  
Underground Engineering ◽  
Inclination Angles ◽  
Loading And Unloading

An experimental study of a rock-like material containing a preexisting fissure subjected to loading and unloading triaxial compression is carried out, and the results show that the mechanical characteristics of the rock-like specimen depend heavily on the loading paths and the inclination of the fissure. The triaxial loading experiment results show that the failure strength linearly increases, while the residual strength linearly decreases with increasing inclination. Furthermore, specimens subjected to triaxial compression show an “X”-type shear failure mode. The triaxial unloading compression experimental results show that specimens with different inclination angles have various failure modes. Specimens with gentle inclinations show a tensile-shear mix failure mode, specimens with middle inclinations show a shear-sliding failure mode, and specimens with steep inclinations show a tensile failure mode. These findings can be used to forecast excavation-induced instabilities in deep underground engineering rock structures.

scholarly journals Failure Behaviour of Sandstone with a Preexisting Joint under Stepped Excavation

2020 ◽  
Vol 2020 ◽  
pp. 1-11
Author(s):  
Yinzhu Liu ◽  
Ping Cao ◽  
Liwen He ◽  
Qibin Lin
Keyword(s):  
Failure Modes ◽  
Shear Failure ◽  
Normal Load ◽  
Crack Coalescence ◽  
Tensile Failure ◽  
Type I ◽  
Failure Characteristics ◽  
Excavation Process ◽  
Spalling Failure ◽  
Shear Slip

Much geotechnical construction needs to be carried out under the condition of stepped excavation. However, there is still a lack of research on crack coalescence and failure modes of jointed rock mass under stepped excavation conditions. In order to simulate the stepped excavation test of the real project, the polylactic acid (PLA) material is selected as the filler for the excavation area. The stepped excavation tests are performed on sandstone specimens containing a preexisting joint under different normal load conditions. The dynamic stepped excavation of simulating excavate rock engineering is realised. The constant normal loads during the excavation process are determined to be 80 kN and 100 kN. The influence of the joint inclination on the failure characteristics of the excavation process is analysed. Four typical failure modes are summarised: (a) Mode I: crack coalescence of tensile failure; (b) Mode II: crack coalescence of mixed failure; (c) Mode III: without crack coalescence of mixed failure; (d) Mode IV: without crack coalescence of shear failure. Furthermore, the failure characteristics of the area above the excavation hole and the preexisting joint are analysed. The results show that there are three failure modes: (a) Type I: spalling failure; (b) Type II: shear slip failure; (c) Type III: shear slip and spalling mixed failure.

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.

A damage constitutive model for rock mass with persistent joints considering joint shear strength

2015 ◽  
Vol 52 (8) ◽  
pp. 1136-1143 ◽  
Author(s):  
Hongyan Liu ◽  
Xiaoping Yuan
Keyword(s):  
Rock Mass ◽  
Constitutive Model ◽  
Failure Modes ◽  
Shear Failure ◽  
Jointed Rock ◽  
Joint Shear Strength ◽  
Rock Mass Strength ◽  
Damage Constitutive Model ◽  
Joint Shear ◽  
Set Up

Microcracks and joints, two types of flaws that appear in a rock mass, affect both the rock mass strength and deformability. A model that can simultaneously reflect the effect of these two types of flaws on the mechanical behavior of a rock mass with persistent joints is not yet available. This study focusses on a microcracked rock mass with persistent joints and establishes a mechanical model, accounting for the anisotropy in the rock mass strength and deformability induced by the existence of the joints. Firstly, the compound damage variable from the coupling macroscopic and mesoscopic flaws is deduced based on the Lemaitre strain equivalence hypothesis. Secondly, the corresponding damage constitutive model for a jointed rock mass is set up. Thirdly, the joint shear failure criterion is incorporated into the constitutive model to extend the model. Finally, the results of the calculation examples show that the existence of the joint will reduce the strength, enlarge the deformability, and lead to anisotropy of the rock mass. A series of calculation examples and comparisons validate that the proposed model is capable of presenting the joint-induced anisotropy in rock mass strength and deformability, determining its possible failure modes, and reasonably simulating its complete stress–strain relationship.

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