A Slate Tunnel Stability Analysis considering the Influence of Anisotropic Bedding Properties

Bedding planes are the fundamental causes of anisotropic deformation and mechanical behaviors in slate, which will have great influence on tunnel stability. In order to analyse tunnel stability surrounded by slate, well-foliated slate in eastern Guizhou was taken as the specimen in tests. Microscopic analysis and test results show that slate can be regarded as a special continuous material. During the test, shear strength parameters and progressive failure varied when the direction of the bedding plane was changed, and two sets of reasonable shear strength were achieved by fitting. Numerical model verification is conducted before applying, and results indicate that the model can represent the anisotropic failure properties. So the model considering anisotropic shear strength simultaneously is utilized to analyse the tunnel stability in slate. When it is medium dip angle, the tunnel is significantly unstable especially for face and side walls, and at 45° (dip angle), the plastic zone depth ahead of the tunnel face can be the largest, being 1.7 times the tunnel height. The maximum deviator stress (σ1 − σ3) is centralized on the middle of the side wall, and also, the stress (σ1 − σ3) is the highest at 45° (dip angle), which will lead to shear failure.

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An Experimental Study on Mechanical Behavior of Parallel Joint Specimens under Compression Shear

Advances in Civil Engineering ◽

10.1155/2018/5428670 ◽

2018 ◽

Vol 2018 ◽

pp. 1-12

Author(s):

Fei Wang ◽

Ping Cao ◽

Yu Chen ◽

Qing-peng Gao ◽

Zhu Wang

Keyword(s):

Shear Stress ◽

Shear Strength ◽

Failure Mode ◽

Shear Failure ◽

Strain Curve ◽

Shear Loading ◽

Plane Shear ◽

Joint Spacing ◽

Dip Angle ◽

Joint Inclination

In order to investigate the influence of the joint on the failure mode, peak shear strength, and shear stress-strain curve of rock mass, the compression shear test loading on the parallel jointed specimens was carried out, and the acoustic emission system was used to monitor the loading process. The joint spacing and joint overlap were varied to alter the relative positions of parallel joints in geometry. Under compression-shear loading, the failure mode of the joint specimen can be classified into four types: coplanar shear failure, shear failure along the joint plane, shear failure along the shear stress plane, and similar integrity shear failure. The joint dip angle has a decisive effect on the failure mode of the specimen. The joint overlap affects the crack development of the specimen but does not change the failure mode of the specimen. The joint spacing can change the failure mode of the specimen. The shear strength of the specimen firstly increases and then decreases with the increase of the dip angle and reaches the maximum at 45°. The shear strength decreases with the increase of the joint overlap and increases with the increase of the joint spacing. The shear stress-displacement curves of different joint inclination samples have differences which mainly reflect in the postrupture stage. From monitoring results of the AE system, the variation regular of the AE count corresponds to the failure mode, and the peak value of the AE count decreases with the increase of joint overlap and increases with the increase of joint spacing.

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Effect of Bedding Orientation and Spatial Variability of Stratification Shear Strength on Stability of Transversely Isotropic Rock Slope

Frontiers in Physics ◽

10.3389/fphy.2021.777216 ◽

2021 ◽

Vol 9 ◽

Author(s):

Su-Hua Zhou ◽

Shuai-Kang Zhou ◽

Jiu-Chang Zhang ◽

Xin Tan

Keyword(s):

Shear Strength ◽

Spatial Variability ◽

Transversely Isotropic ◽

Transversely Isotropic Rock ◽

Direct Shear Tests ◽

Isotropic Rock ◽

Bedding Planes ◽

Dip Angle ◽

The Stability ◽

Surface Changes

The spatial variability of soil properties is inherent. A series of direct shear tests were carried out on strongly weathered slates samples with weak bedding planes, the result of which indicates the existence of variability of shear strength parameters. Based on the testing results, several numerical simulations of slopes were conducted considering such a variability of shear strength. The results had shown that the weak bedding planes affect the shape of sliding arc as well as the factor of safety of slopes. As the dip angle of bedding planes increases, the shape of the sliding surface changes from circular to a mixed form of circular and planner. When incorporating the spatial variability of weak planes’ shear strength into the stability analysis, the safety factors of slopes would reduce, in which the sliding arc exhibited a sliding band comprising multiple sets of sliding arcs.

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Stability Analysis of the Nanjung Water Diversion Twin Tunnels based on Convergence Measurement

Indonesian Mining Professionals Journal ◽

10.36986/impj.v1i1.11 ◽

2019 ◽

Vol 1 (1) ◽

pp. 49-60

Author(s):

Simon Heru Prassetyo ◽

Ganda Marihot Simangunsong ◽

Ridho Kresna Wattimena ◽

Made Astawa Rai ◽

Irwandy Arif ◽

...

Keyword(s):

Stability Analysis ◽

Convergence Rate ◽

Critical Strain ◽

Convergence Rates ◽

Strain Analysis ◽

Water Diversion ◽

Tunnel Face ◽

Tunnel Stability ◽

The Stability ◽

Twin Tunnels

This paper focuses on the stability analysis of the Nanjung Water Diversion Twin Tunnels using convergence measurement. The Nanjung Tunnel is horseshoe-shaped in cross-section, 10.2 m x 9.2 m in dimension, and 230 m in length. The location of the tunnel is in Curug Jompong, Margaasih Subdistrict, Bandung. Convergence monitoring was done for 144 days between February 18 and July 11, 2019. The results of the convergence measurement were recorded and plotted into the curves of convergence vs. day and convergence vs. distance from tunnel face. From these plots, the continuity of the convergence and the convergence rate in the tunnel roof and wall were then analyzed. The convergence rates from each tunnel were also compared to empirical values to determine the level of tunnel stability. In general, the trend of convergence rate shows that the Nanjung Tunnel is stable without any indication of instability. Although there was a spike in the convergence rate at several STA in the measured span, that spike was not replicated by the convergence rate in the other measured spans and it was not continuous. The stability of the Nanjung Tunnel is also confirmed from the critical strain analysis, in which most of the STA measured have strain magnitudes located below the critical strain line and are less than 1%.

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Failure Process Simulation of Interlayered Rocks under Compression

Advances in Civil Engineering ◽

10.1155/2018/9615457 ◽

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.

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Study on Stability and Plastic Zone Distribution of Tunnel with Thin Carbonaceous Slate at Different Dip Angles

Shock and Vibration ◽

10.1155/2021/6345879 ◽

2021 ◽

Vol 2021 ◽

pp. 1-10

Author(s):

Jin Zhang ◽

Chuanhao Xi ◽

Qian Zhang ◽

Mengxue Wang

Keyword(s):

Tensile Strength ◽

Plastic Zone ◽

Field Measurement ◽

Joint Angle ◽

Rock Joint ◽

Great Influence ◽

Surrounding Rock ◽

Test Field ◽

Maximum Displacement ◽

Dip Angle

Carbonaceous slate is heterogeneous and anisotropic, which has a great influence on the stability of tunnel. In this paper, by means of laboratory test, field measurement, and numerical simulation, the surrounding rock stability and plastic zone distribution characteristics of the carbonaceous slate tunnel at different intersection angles are analyzed. First, combined with the Haibaluo tunnel project, Brazilian splitting and uniaxial compression tests of jointed carbonaceous slate are performed. The test results show that the tensile strength of carbonaceous slate is related to joint dip angle. When the joint angle is 0°, the tensile strength is the largest and decreases with the increase of the joint angle. The uniaxial strength of rock decreases first and then increases. Based on the discrete fracture network (DFN) technology, a calculation model is established. The calculation results show that the maximum displacement is 0.45 m, when the dip angle of the surrounding rock joint is 45°. The field measurement also shows that the dip angle of the surrounding rock joint has an important influence on the distribution of the plastic zone. When the joint dip angle is 45°, the plastic zone develops most strongly.

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Fatigue Life Prediction of Rolling Bearings Based on Modified SWT Mean Stress Correction

10.21203/rs.3.rs-132643/v1 ◽

2020 ◽

Author(s):

Aodi Yu ◽

Hong-Zhong Huang ◽

Yan-Feng Li ◽

He Li ◽

Ying Zeng

Keyword(s):

Fatigue Life ◽

Life Prediction ◽

Stress Ratio ◽

Prediction Models ◽

Great Influence ◽

Sensitivity Coefficient ◽

Model Verification ◽

Mean Stress ◽

Test Results ◽

Rolling Bearings

Abstract Mean stress has a great influence on fatigue life, commonly used stress-based life prediction models can only fit the test results of fatigue life under specific stress ratio or mean stress but cannot describe the effect of stress ratio or mean stress on fatigue life. Smith, Watson and Topper (SWT) proposed a simple mean stress correction criterion. However, the SWT model regards the sensitivity coefficient of all materials to mean stress as 0.5, which will lead to inaccurate predictions for materials with a sensitivity coefficient not equal to 0.5. In this paper, considering the sensitivity of different materials to mean stresses, compensation factor is introduced to modify the SWT model, and several sets of experimental data are used for model verification. Then, the proposed model is applied to fatigue life predictions of rolling bearings, and the results of proposed method are compared with test results to verify its accuracy.

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Face Stability Analysis of Shield Tunnels in Homogeneous Soil Overlaid by Multilayered Cohesive-Frictional Soils

Mathematical Problems in Engineering ◽

10.1155/2016/1378274 ◽

2016 ◽

Vol 2016 ◽

pp. 1-9 ◽

Cited By ~ 10

Author(s):

Kaihang Han ◽

Chengping Zhang ◽

Wei Li ◽

Caixia Guo

Keyword(s):

Failure Mechanism ◽

Shear Failure ◽

Three Dimensional ◽

Earth Pressure ◽

Support Pressure ◽

Tunnel Face ◽

Arch Effect ◽

Theory Approximation ◽

Homogeneous Soil ◽

Frictional Soils

In order to better interpret failure features of the failure of soil in front of tunnel face, a new three-dimensional failure mechanism is proposed to analyze the limit support pressure of the tunnel face in multilayered cohesive-frictional soils. The new failure mechanism is composed of two truncated cones that represent the shear failure band and a distributed force acting on the truncated cones that represents the pressure arch effect. By introducing the concept of Terzaghi earth pressure theory, approximation of limit support pressures is calculated using the limit analysis methods. Then the limit support pressures obtained from the new failure mechanism and the existing approaches are compared, which show that the results obtained from the new mechanism in this paper provide relatively satisfactory results.

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Experimental study on deformation and failure characteristics of discontinuous prefabricated fractured tuff

Journal of Geophysics and Engineering ◽

10.1093/jge/gxz052 ◽

2019 ◽

Vol 16 (5) ◽

pp. 862-874

Author(s):

Yang Song ◽

Heping Wang ◽

Meng Ren

Keyword(s):

Shear Failure ◽

Failure Process ◽

Dissipated Energy ◽

Uniaxial Compression Test ◽

Tensile Shear ◽

Joint Spacing ◽

Failure Characteristics ◽

Deformation And Failure ◽

Peak Intensity ◽

Dip Angle

Abstract To study more fully the characteristic law of deformation and failure of tuff jointed rock mass of prefabricated parallel discontinuous joint test specimens, the uniaxial compression test was used. The stress–strain curve, peak intensity, deformation parameters, energy characteristics, etc., of the rock test specimens were systematically studied under different combinations of joint dip angle and joint spacing. The research found that: (1) during the failure process of tuff, the peak intensity and elastic modulus followed a U-shaped change pattern and the minimum value was reached when α = 60°; (2) the fracture modes of test specimens with different joint dip angles were different. When α = 30° and 45°, failure characteristics were mixed modes of tensile or tensile shear failure. When α = 60°, failure characteristics were shear. At α = 75°, the failure characteristic was tensile shear failure. (3) The absorbed and dissipated energy of the rock increased nonlinearly at each stage of deformation. (4) We quantified rock energy damage through a correlation between dissipated energy and absorbed energy of the rock in the process of energy evolution, and obtained an evolution of the relationship between the dissipated energy ratio, crack dip angle and crack spacing. Based on different fracture distribution methods and according to the strain equivalence principle, the constitutive equation of the pre-peak rock damage was obtained.

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Experimental Study on Hydromechanical Behavior of an Artificial Rock Joint with Controlled Roughness

Sustainability ◽

10.3390/su11041014 ◽

2019 ◽

Vol 11 (4) ◽

pp. 1014

Author(s):

Seungbeom Choi ◽

Byungkyu Jeon ◽

Sudeuk Lee ◽

Seokwon Jeon

Keyword(s):

Rock Mass ◽

Rock Joint ◽

Great Influence ◽

Rock Joints ◽

In Situ Tests ◽

Joint Roughness ◽

Artificial Rock ◽

Geometric Conditions ◽

Bedding Planes ◽

Hydraulic Aperture

Rock mass contains various discontinuities, such as faults, joints, and bedding planes. Among them, a joint is one of the most frequently encountered discontinuities in rock engineering applications. Generally, a joint exerts great influence on the mechanical and hydraulic behavior of rock mass, since it acts as a weak plane and as a fluid path in the rock mass. Therefore, an accurate understanding on joint characteristics is important in many projects. In-situ tests on joints are sometimes consumptive in terms of time and expenses so that the features are investigated by laboratory tests, providing fundamental properties for rock mass analyses. Although the behavior of a joint is affected by both mechanical and geometric conditions, the latter are often limited, since quantitative control on the conditions is quite complicated. In this study, artificial rock joints with various geometric conditions, i.e., joint roughness, were prepared in a quantitative manner and the hydromechanical characteristics were investigated by several laboratory experiments. Based on the results, a prediction model for hydraulic aperture was proposed in the form of ( e h / e m ) 3 = exp ( − 0.0462 c ) × ( 0.8864 ) J R C , which was a function of the mechanical aperture, joint roughness, and contact area. Relatively good agreement between the experimental results and predicted value indicated that the model is capable of estimating the hydraulic aperture properly.

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A New Shear Strength Criterion for Rock Masses with Non-Persistent Discontinuities Considering the Nonlinear Progressive Failure Process

Materials ◽

10.3390/ma13214694 ◽

2020 ◽

Vol 13 (21) ◽

pp. 4694

Author(s):

Bowen Zheng ◽

Shengwen Qi ◽

Songfeng Guo ◽

Xiaolin Huang ◽

Ning Liang ◽

...

Keyword(s):

Shear Strength ◽

Friction Coefficient ◽

Progressive Failure ◽

Strength Criterion ◽

Rock Masses ◽

Basic Form ◽

Shear Strength Criterion ◽

Nonlinear Shear ◽

New Criterion ◽

Internal Friction Coefficient

The shear strength characteristics of rock masses containing non-persistent discontinuities are strongly affected by discontinuities and rock bridges. The linear Jennings criterion cannot reflect the nonlinear mechanical behavior during progressive failure of rock masses with non-persistent discontinuities. In this study, a new nonlinear shear strength criterion was developed. First of all, a series of shear test data about artificial rock mass samples were collected on the basis of the published literatures, and five types of samples were differentiated according to the positions of discontinuities. After that, a new nonlinear shear strength criterion was proposed by introducing two correction coefficients A and B into the basic form of the Jennings criterion, which could correct the weight of the cohesion and the internal friction coefficient of rock bridges respectively. Then, the new criterion was determined by fitting the basic form of the Jennings criterion with the laboratory data. It was found that the parameters A and B had a nonlinear exponential and negative exponential relation with the connectivity rate respectively. It indicated that both the cohesion and the internal friction coefficient estimated by the new criterion were superior to those estimated by the Jennings criterion. Compared with the linear Jennings criterion, the new nonlinear shear strength criterion had a better applicability.

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