Tunnel failure mechanism during loading and unloading processes through physical model testing and DEM simulation

AbstractGeo-materials may present varying mechanical properties under different stress paths, especially for tunnel excavation, which is typically characterized by the decreased radial stress and increased axial stress during the complex loading and unloading process. This study carried out a comparative analysis between the loading and unloading model testing, which was then combined with PFC2D simulation, aiming to reveal the fracture propagation pattern, microscopic stress and force chain distribution of the rock mass surrounding the tunnel. Comparisons of extents and development of tensile strain between loading and unloading testing results were made. The overall stability, the integrity of rock mass, and the failure pattern transition under loading and unloading processes were systematically examined. In addition, for the two unloading cases with different vertical stresses imposed, the failure patterns were both identified as the collapse of the V − shaped extruded sidewall, due to the coupling of the shear failure and the vertical tensile failure in the sidewall wedge.

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Study on Failure of Rock Mass around Deep Tunnel

Applied Mechanics and Materials ◽

10.4028/www.scientific.net/amm.99-100.370 ◽

2011 ◽

Vol 99-100 ◽

pp. 370-374 ◽

Cited By ~ 1

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.

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Investigation for Influences of Seepage on Mechanical Properties of Rocks Using Acoustic Emission Technique

Geofluids ◽

10.1155/2020/6693920 ◽

2020 ◽

Vol 2020 ◽

pp. 1-10

Author(s):

Saisai Wu ◽

Xiaohan Zhang ◽

Junping Li ◽

Zhao Wang

Keyword(s):

Mechanical Properties ◽

Acoustic Emission ◽

Rock Mass ◽

Shear Failure ◽

Great Influence ◽

Average Energy ◽

Acoustic Emission Technique ◽

Failure Patterns ◽

Initial Rupture ◽

Emission System

The behavior of rock mass is governed by the properties of both the rock material and discontinuities in the rock mass. Surrounding environments including the existence of water also have a great influence on the behavior and mechanical properties of rocks. In this study, a novel-designed compression and seepage testing system, associated with an acoustic emission system, was designed and constructed. The changes in the specimens resulting from the uniaxial compression were monitored by an acoustic emission technique. The characteristics of the acoustic emission parameters at different stages including compaction and crack initiation, crack propagation, and catastrophic failure were analyzed. The existence of seepage had direct influences on the mechanical properties and failure patterns of the specimens. The specimens tested in pure compression conditions demonstrated strong burst proneness and ruptured into separate pieces, while for the specimens with seepage, no burst proneness was observed and the specimens tended to fail along a macroscopic shear failure plane. The highest average energy of the acoustic signal occurred at the stage of initial rupture of rock specimens, rather than at the stage of widespread rupture. The studies explored the possibilities of using the acoustic emission technique to investigate the problems associated with the seepage in geotechnical and rock engineering and provided meaningful results for further research in this field.

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

International Journal of Applied Mechanics ◽

10.1142/s1758825112500366 ◽

2012 ◽

Vol 04 (03) ◽

pp. 1250036 ◽

Cited By ~ 2

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.

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Study on the Generation Mechanism and Development Law of the Zonal Disintegration in Deep Burial Tunnels

Shock and Vibration ◽

10.1155/2020/6431048 ◽

2020 ◽

Vol 2020 ◽

pp. 1-16

Author(s):

Xiaohui Ma ◽

Jihong Wei ◽

Jin Liu ◽

Zezhuo Song ◽

Yuxia Bai

Keyword(s):

Mechanical Properties ◽

Rock Mass ◽

Maximum Stress ◽

Axial Stress ◽

Axial Direction ◽

Tensile Failure ◽

Zonal Disintegration ◽

Nonlinear Characteristics ◽

Deep Rock ◽

New Phenomena

In the development of underground spaces, we found that the mechanical properties of rock mass often demonstrate strong nonlinear characteristics. Some new phenomena emerge in deep rock mass engineering. This includes zonal disintegration and rock burst. Zonal disintegration is very important in deep tunnels. In this paper, we start with the mechanical properties of deep rocks to understand the preconditions for zonal disintegration. Using the Failure Approach Index (FAI), the process of zonal disintegration can be modeled by FLAC (FISH language). Our results indicate that tensile failure in the Supporting Pressure Zone (SPZ) is a precondition for zonal disintegration. Various factors that affect the generation of zonal disintegration are studied. When the maximum stress is in the axial direction, zonal disintegration will be present in deep tunnels. The high axial stress is necessary for zonal disintegration. We will present a zonal disintegration simulation in one coal mine for comparison with the borehole teleview data. We suggest some measures to prevent the development of zonal disintegration.

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

Advances in Civil Engineering ◽

10.1155/2020/9374352 ◽

2020 ◽

Vol 2020 ◽

pp. 1-12 ◽

Cited By ~ 2

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.

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

Science Progress ◽

10.1177/00368504211021694 ◽

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.

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The dynamic characteristics of backfill made of mining waste at one-dimensional dynamic and static loading

Revista Internacional de Métodos Numéricos para Cálculo y Diseño en Ingeniería ◽

10.23967/j.rimni.2021.04.002 ◽

2021 ◽

Vol 37 (1) ◽

Author(s):

X. Yang ◽

Y. Zhang

Keyword(s):

Shear Failure ◽

Split Hopkinson Pressure Bar ◽

Axial Stress ◽

Critical Role ◽

Tensile Failure ◽

Hopkinson Pressure Bar ◽

Axial Pressure ◽

Confining Stress ◽

Mining Operations ◽

Shpb Test

Backfill is widely used in underground mines around the world for its effective reduction in environmental impact of mining operations by utilizing a part of mine waste as underground backfill material. The strength of backfill plays a critical role in improving stop stability and preventing surface subsidence. In this paper, a series of SHPB (Split Hopkinson Pressure Bar) tests with different strain rates and static axial pressures are conducted. The results show that: (1) The dynamic strength of the backfill specimen increases first and then decreases with the increase of static axial pressure. It reaches a maximum when the static axial pressure reaches 30% of the static compressive strength in the SHPB test. (2) The stress-strain curves of backfill specimens can be divided into three stages: elastic stage, yield stage and failure stage. The compaction stage is obscure. The backfill specimens are not sensitive at low strain rate. (3)With the increase of incident energy, the absorbed energy mounts. (4) The failure mode of the backfill specimen is tensile failure when static axial pressure is 0MPa in the SHPB test while it becomes compression shear failure when static axial pressure is higher than 0MPa. (5) The backfill specimen is very compressed when it is loaded with axial stress and confining stress simultaneously. This compression property of backfill specimen may be related to the nature of hydration products at different curing times, which requires further research in the future.

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The Role of Elasto-Plasticity in Cavity Shape and Sand Production in Oil and Gas Wells

SPE Journal ◽

10.2118/187225-pa ◽

2018 ◽

Vol 24 (02) ◽

pp. 744-756 ◽

Cited By ~ 4

Author(s):

Haotian Wang ◽

Mukul M. Sharma

Keyword(s):

Shear Failure ◽

Oil And Gas ◽

Shear Bands ◽

Failure Criteria ◽

Tensile Failure ◽

Production Model ◽

Sand Production ◽

Plastic Properties ◽

Cavity Shape ◽

Failure Patterns

Summary Previous experimental observations have shown the formation of distinct failure patterns and cavity shapes under different stress and flow conditions. With isotropic stress, spiral failure patterns with localized shear bands are likely to form. On the other hand, under anisotropic stress, V-shaped cavities, dog-ear cavities, or slit-mode cavities are usually observed. However, the mechanisms for the development of these sanding cavities have not been fully articulated. In addition, to accurately predict the onset of sanding and to predict the sand-production rate, it is crucial to capture the physics of the formation of these cavities during sand production. This paper presents a fully coupled poro-elasto-plastic, 3D sand-production model for sand-production prediction around openhole and perforated wellbores in a weakly consolidated formation. Sanding criteria are based on a combination of shear failure, tensile failure, and compressive failure from the Mohr-Coulomb theory and strain-hardening/softening. After the failure criteria are met, an algorithm for the entrainment of the sand based on the calculation of hydrodynamic forces is implemented to predict sand erosion and transport. Dynamic mesh refinement has been implemented to effectively capture the strain-localization regions. The model has been validated with multiple analytical solutions. In addition, it is applied to compare with previous sand-production experiments that have explored the different cavity shapes formed under different conditions. The model is capable of not only explaining the mechanisms responsible for each type of cavity shape but also predicting the cavity shape that will be formed under a specific set of conditions. Parametric studies for these cases provide an additional insight into the important role that the post-yield, poro-elasto-plastic properties of the sand play in controlling the sanding mechanisms and cavity development. This allows us to predict, much more accurately, the onset of sanding and the sanding rate.

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The mechanical behaviour of rock specimens with specific edge crack distributions under triaxial loading conditions

Journal of Geophysics and Engineering ◽

10.1093/jge/gxz059 ◽

2019 ◽

Vol 16 (5) ◽

pp. 962-973 ◽

Cited By ~ 1

Author(s):

Guoyong Duan ◽

Jianlin Li ◽

Jingyu Zhang ◽

Zuosen Luo ◽

Liangpeng Wan ◽

...

Keyword(s):

Mechanical Behaviour ◽

Shear Failure ◽

Axial Stress ◽

Triaxial Compression ◽

Confining Pressure ◽

Loading Conditions ◽

Compression Tests ◽

Joint Orientation ◽

Failure Patterns ◽

Rock Specimens

Abstract Research on the mechanical behaviour of rock masses with multiple joints has become a popular topic and has practical applications in natural slope stability. This paper aims to clarify the influence of joint geometry, joint orientation and joint connectivity ratio on the mechanical behaviour of rock specimens containing two pre-existing joints. Triaxial compression tests were conducted under various confining pressures to simulate the variation in external conditions. An exponential criterion was used to describe the relationship between the axial stress and confining pressure. The experimental crack propagation was explored by varying the joint orientation, joint connectivity ratio and confining pressure. The structural plane with a greater angle of inclination controlled the failure of the rock sample. Two failure patterns were observed under the loading conditions: shear failure and mixed failure. The failure surface trajectory presented similar deviations with the increase in joint inclination angle, joint connectivity ratio and confining pressure, which also accelerates the transition from mixed failure to shear failure. The experimental results highlight the significance of elucidating the influence of structural planes in practical engineering to predict the stability of natural slopes.

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New Interface for Assessing Wellbore Stability at Critical Mud Pressures and Various Failure Criteria: Including Stress Trajectories and Deviatoric Stress Distributions

Energies ◽

10.3390/en12204019 ◽

2019 ◽

Vol 12 (20) ◽

pp. 4019

Author(s):

Wang ◽

Weijermars

Keyword(s):

Shear Failure ◽

Axial Stress ◽

Failure Criteria ◽

Wellbore Stability ◽

Tensile Failure ◽

Wellbore Instability ◽

Wellbore Pressure ◽

Stress States ◽

Deviatoric Stresses ◽

Wellbore Failure

This study presents a new interface for wellbore stability analysis, which visualizes and quantifies the stress condition around a wellbore at shear and tensile failure. In the first part of this study, the Mohr–Coulomb, Mogi–Coulomb, modified Lade and Drucker–Prager shear failure criteria, and a tensile failure criterion, are applied to compare the differences in the critical wellbore pressure for three basin types with Andersonian stress states. Using traditional wellbore stability window plots, the Mohr–Coulomb criterion consistently gives the narrowest safe mud weight window, while the Drucker–Prager criterion yields the widest window. In the second part of this study, a new type of plot is introduced where the safe drilling window specifies the local magnitude and trajectories of the principal deviatoric stresses for the shear and tensile wellbore failure bounds, as determined by dimensionless variables, the Frac number (F) and the Bi-axial Stress scalar (χ), in combination with failure criteria. The influence of both stress and fracture cages increases with the magnitude of the F values, but reduces with depth. The extensional basin case is more prone to potential wellbore instability induced by circumferential fracture propagation, because fracture cages persists at greater depths than for the compressional and strike-slip basin cases.

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