Shear properties and pore structure characteristics of soil–rock mixture under freeze–thaw cycles

Bulletin of Engineering Geology and the Environment - Soil–rock mixtures (S-RMs) are widely distributed in the shallow surfaces of cold regions that experience frequent freeze–thaw...     

Experimental investigation on seepage erosion of the soil–rock interface

Bulletin of Engineering Geology and the Environment - Internal erosion under seepage flow affects the hydraulic and mechanical behavior of the soil, which is one of the most important factors of...     

Correction to: Shear properties and pore structure characteristics of soil–rock mixture under freeze–thaw cycles

Bulletin of Engineering Geology and the Environment - A Correction to this paper has been published: https://doi.org/10.1007/s10064-021-02169-7     

Realization of uniform deformation of soil specimen under undrained plane strain condition based on soil–water coupled finite deformation analysis considering inertia forces

Based on a soil–water coupled finite deformation analysis, theoretical considerations and numerical calculations were carried out under the undrained plane strain condition in order to reproduce a uniform deformation field. Rather than the “quasi-static” equation of motion, which does not include inertia forces, a dynamic equation of motion which includes inertia forces was used. At first, a theoretical consideration was carried out to realize uniform deformation for a saturated soil that satisfied the element-wise undrained/constant-volume condition. This presents an “infinitely slow loading” case without ignoring the inertia term based on the u–p formulation. In other words, it can be seen that under general slow loading that is not infinitely slow, a gradient in the pore water pressure will always be produced, resulting in the migration of pore water and loss/collapse of uniformity. This first conclusion is useful for verifying numerical analysis code made in the finite deformation regime. Next, the uniform deformation of a plane strain rectangular soil specimen was measured under constant cell pressure and undrained boundary conditions using a dynamic soil–water coupled analysis in which the SYS Cam-clay model was employed as the elasto-plastic constitutive model for the soil skeleton. In addition, the effects of the loading rates as well as loading applications, with/without inertia forces, on the loss of uniformity in deformation were shown to have a significant influence on the inertia term even though the loss itself was extremely small.     

Seepage–stress coupled analysis on anisotropic characteristics of the fractured rock mass around roadway

Anisotropic properties of the fractured rock masses are investigated considering the coupled effect of the seepage and stress. The equivalent permeability and damage tensor of the fractured rock mass are initially examined using a series of Discrete-Fracture-Network (DFN) models with varied size and orientations from the geological investigation data of the sandstone roadway on the floor of 12# coal seam in Fangezhuang Coal Mine. A seepage–stress cross-coupling anisotropic model considering the coupled effect of the seepage and stress is described and applied to analyze the influence of the principal orientations of the joint sets on the anisotropic properties of the rock mass. It appears that the anisotropic properties of the rock mass have a great influence on the stress distribution, hydraulic conductivity coefficient and damage zone. The model may contribute to a more reasonable explanation on the dominant effect of the joint sets on deformation and failure of rock mass.     

Investigation of geotextile–soil interaction under a cyclic vertical load using the discrete element method

Geotextiles are often used in roadway construction as separation, filtration, and reinforcement. Their performance as reinforcement in geotextile-reinforced bases depends on geotextile–soil interaction. This paper investigates the geotextile–soil interaction under a cyclic wheel load using the Discrete Element Method (DEM). In this study, soil was modeled as unbonded particles using the linear contact stiffness model, and the geotextile was modeled as bonded particles. The micro-parameters of the soil and the geotextile were determined using biaxial tests and a tensile test, respectively. The influence of the placement depth and the stiffness of the geotextile on the performance of the reinforced base was investigated. The DEM results show that the depth of the geotextile significantly affected the degree of interaction between the geotextile and the soil. Under the applied cyclic vertical load, the geotextile developed a low tensile strain. The effect of the stiffness of the geotextile on the deformation was more significant when the geotextile was placed at a shallower location than when placed at a deeper location.     

Effect of Bermuda grass root on mechanical properties of soil under dry–wet cycles

Bulletin of Engineering Geology and the Environment - It has been proved that Bermuda grass root is an effective material to improve the mechanical properties of soil, but the effect of the...     

Effect of surrounding soil on stress–strain response of buried pipelines under ground loads

In order to determine the stress–strain response of buried pipelines under the ground load, the pipeline–soil coupling finite element model was established. The mechanical behaviours of buried pipelines in the soil stratum and the rock stratum, as well as the effects of surrounding soil's elasticity modulus, Poisson's ratio and cohesion on stress and strain of buried pipelines were investigated. The results show that the maximum von Mises stress, high stress area, axial strain and plastic strain increase with the increasing ground load. Buried pipeline in the soil stratum is more prone to failure than in the rock stratum under the same ground load. The maximum axial compressive strain appears at the bottom of buried pipelines when there is no buckling, and the maximum tensile strain appears on the two sides. High stress area, the axial strain, the plastic strain and the plastic area decrease with the increase of the soil's elasticity modulus and cohesion. But the surrounding soil's Poisson's ratio has a small effect on the stress and strain of buried pipelines under the ground load. The results can provide a theoretical basis and reference for safety evaluation, repair and maintenance of buried pipelines.     

Effect of soil–infilled joints on the stability of rock wedges formed in a tunnel roof

The use of an equivalent continuum for a rock mass is not always suitable for situations, where the failure is structurally controlled by discontinuities as in the case of wedges in the tunnel roof. In these instances, discontinuum approaches are usually preferred. Rock joints that are filled with soft infill are likely to be the weakest planes in a rock mass, having a dominant influence on its overall shear behaviour. In this case, the joint material model adopted for the discontinuities should be able to describe important mechanisms, such as asperity sliding and shearing, post-peak behaviour, asperity deformation, and the effect of the soft infilling. The latest version of a soil–infilled joint model is discussed here. It describes more comprehensively than previous models the occurrence of dilation and compression with lateral displacements, and also represents the hardening mechanism related to asperity interference as observed in the laboratory that cannot be readily captured by the existing joint models. An analytical approach for the analysis of rock wedges structurally controlled by soil–infilled joints and a numerical simulation based on a metro station collapse which occurred in Brazil in 2007 are presented.     

Structural damage and shear performance degradation of fiber–lime–soil under freeze–thaw cycling

The freeze–thaw cycling damages the soil structure, and the shear performance of soil are degraded. A series of tests on lime–soil(L–S) and fiber–lime–soil(F–L–S), including freeze–thaw test, the triaxial compression test, nuclear magnetic resonance (NMR) test and scanning electron microscope (SEM) test, were completed. The test results showed that fiber reinforcement changed the stress–strain behavior and failure pattern of soil. The cohesion and internal friction angle of soil gradually decreased with the increase of freeze–thaw cycles (F–T cycles). The pore radius and porosity of soil increased, while the micro pore volume decreased, and the small pore volume, medium pore volume and large pore volume increased, and the large pore volume had a little variation after 10 F–T cycles. The number of pores of F–L–S was less than L–S, demonstrating that the addition of fiber helped to reduce the pore volume. The interweaved fibers limited the development and the connection of cracks. By means of the spatial restraint effect of fiber on the soil and the friction action between fiber and soil, the shear performances and freeze–thaw durability of F–L–S better were than that of L–S.     

Development and verification of a soil–water coupled finite deformation analysis based on u–w–p formulation with fluid convective nonlinearity

Most soil–water coupled analyses of saturated soil are based on the u–p formulation, where a set of equations is reduced by assuming that the acceleration of the fluid phase relative to that of the solid phase is less than that of the solid phase. Therefore, this analysis cannot be used for a coupled analysis with dynamic water flow in highly permeable soil. This study aims to present a soil–water coupled finite deformation analysis method based on full formulation, or u–w–p formulation. This method differs from conventional methods in the following ways: (1) the governing equations explicitly include the equation of motion for the fluid phase, (2) a relative convective term is used to describe a change in the relative configuration between the two phases, and (3) the moving/inclined discharge boundary is directly implemented to the discretized governing equations. Herein, one/two dimensional seepage and plane-strain deformation analysis results are reported. In the seepage analysis, accelerating permeation of pore water is obtained and the undrained constraint condition is verified. In the deformation analysis, dynamic migration in a high permeable soil specimen, i.e., wave propagation and rotational flow of pore water, is observed.     

Strength parameter identification and application of soil–rock mixture for steep-walled talus slopes in southwestern China

Soil–rock mixture (SRM) is a heterogeneous geomaterial which is widely used in geotechnical engineering projects. As a special engineering geological body, SRM is composed of many complex components and is a heterogeneous multiphase material with various structural characters, and, thus, exhibits complex mechanical characteristics. The mechanical and physical properties of SRM are major factors which lead to different developmental patterns and deformation characteristics for talus slides. The formation mechanism and mechanical parameters of SRM also play important roles in research regarding slope stability. Taking the Mahe talus slide of the Lenggu hydropower station located on the Yalong River in southwestern China as a study example, many methods, such as the analogy method used in engineering, as well as laboratory model tests, large in situ shear tests, the back analysis method and numerical experiments, are applied in the comprehensive analysis of SRM from a macroscopic–microscopic perspective. The SRM samples collected from the Mahe talus slide consist of various soil and rock contents. The parameters gained from the frontal methods are applied in the stability of the Mahe talus slide. The main contents of the study are as follows: (1) according to the special structure of SRM, ten groups of SRM samples collected from different slide parts are used to perform particle size analysis experiments. The grading combination of the ten groups of samples is analyzed and the gradation curves are obtained from laboratory tests; (2) based on the intensive considerations of different particle compositions, the ten SRM group samples collected from the talus slide are used to perform direct shear tests; (3) due to the fact that the samples containing large-sized particles cannot be simulated by means of indoor direct shear tests, large in situ SRM shear tests are performed in the field; (4) SRM containing large-size particles is used to carry out numerical experiments using the similarity ratio, which is determined by contrasting the results of the laboratory tests and numerical experiments for the same size samples containing the same particle combinations. The numerical experiments are then adopted to obtain the shear strength parameters of different large size samples containing different particle combinations from the perspectives of rock content, particle size, and particle graduation; (5) according to the terrain, geomorphology and stability of the talus slide, the shear strength parameters in the case of natural conditions and magnitude 6 earthquakes on the Richter Scale are obtained using the back analysis method from the perspective of the limit equilibrium of the talus slide; and (6) the shear strength parameters of the various methods listed above are contrast-analyzed. The general shear strength parameters of the SRM are attained properly by using the weighted superposition of the safety coefficients from the different calculation methods. The general strength parameters are used to calculate the stability factor of the Mahe talus slide.     

Case studies of TBM tunneling performance in rock–soil interface mixed ground

This paper investigates the performance of tunnel boring machines (TBMs) in rock–soil mixed-face ground based on TBM tunneling projects in Singapore. Currently several methods are available to estimate TBM tunneling performance in homogenous rock or soil. However, the existing models cannot be effectively applied to predict TBM penetration rate in mixed ground. The tunnels in this study were excavated in adverse mixed-face ground conditions. The geological profiles and the TBM operational parameters are compiled and analyzed. The influence of different geological face compositions on the performance of the TBMs is studied. The statistical analysis shows that there is a possible correlation between the mixed-face ground characteristics and the TBM advancement. Different approaches are used to find a reliable model. Finally, a method is proposed to predict the TBM performance in mixed-face ground for project planning and optimization.     

Investigation of the effects of wetting–drying and freezing–thawing cycles on some physical and mechanical properties of selected ignimbrites

This study was performed to investigate the changes in the physical and mechanical parameters of ignimbrites of different colors (black, red, yellow, gray) from Central Anatolia under the influence of wetting–drying and freezing–thawing cycles. For this purpose, 96 NX-size core samples were prepared. The unit weight, specific gravity, apparent porosity, water absorption by weight, slake durability index, uniaxial compressive strength, and P-wave velocity of each ignimbrite sample before conversion were determined. All of these parameters were then redetermined every 10 cycles (for a total of 50 cycles) for each sample. The changes in the values of the parameters after these set numbers of cycles were evaluated statistically. The petrographic and chemical compositions of the volcanic rocks influence their physical and mechanical properties, so some changes were also observed in the ignimbrite samples after these physical processes. Freezing and thawing cycles were observed to have an obvious impact on the physical and mechanical properties of the samples. The greatest changes were observed in black ignimbrite (with ferromagnesian minerals).     

Influence of initial dry density and water content on the soil–water characteristic curve and suction stress of a reconstituted loess soil

In the northwest of China, many loess landslides have occurred without clear triggering factors (i.e., rainfall, earthquake, human activities, etc.). To better understand and analyze the hydro-mechanical properties of these slopes and then provide evidence for their stability analysis subjected to matric suction, it is essential to clarify the soil–water characteristic curve (SWCC). In this study, we conducted a set of experimental trials to examine the influences of initial dry density, water content upon the SWCCs of a loess soil taken from a loess landslide area, by using a conventional volumetric pressure plate extractor. Two common SWCC models have been investigated to evaluate which one is better for loess soil. The suction stress characteristic curves (SSCCs) were also estimated and analyzed. We found that behaviors of SWCCs would be different when the matric suction was greater than a certain value. The two SWCC equations have approximately the same performance in describing the SWCC. The rates of desorption decrease and residual water content increases with increasing the initial dry density, while the initial dry density has little, if any, influence on the air-entry value (AEV). The specimen compacted under higher initial water content would exhibit a higher AEV value and residual water content but lower rate of desorption as compared with the lower initial water content. The magnitude of suction stress had an approximately linear relationship with matric suction before the AEV value, the SSCC shapes will be markedly varied with the initial dry density and water content.     

Study of failure mechanisms of rock under compressive–shear loading using real-time laser holography

Failure of rock is quite commonly induced by compressive and shear coupling loading. The knowledge of the mechanism and process of deformation and failure of rock under compressive–shear loading condition is an important basis for the study of stability of rock engineering. Based on the principles of laser holographic interferometry, an experimental system with high precision has been established. Through the experiment, the real-time laser holographic interferential fringes under compressive–shear loading are simultaneously observed and recorded. The active fringes can visually display the distribution, mode, moving path and dynamic evolution of deformation and cracking in rock. On the basis of interpretation and quantitative analysis of the active fringes, the whole process of deformation and failure of rock, including time–spatial evolution law of initiating, propagating, growing and closing of cracks in rock, is quantitatively described. From the experimental results, some conclusions on the mechanism and characters of deformation and failure of rock under compressive–shear loading condition are drawn out.     

On the frictional property of lubricants and its impact on jacking force and soil–pipe interaction of pipe-jacking

Lubricants are frequently applied in pipe-jacking, especially under difficult geological conditions or in cases of a longer alignment. The main purpose of lubricant application is to reduce the friction between pipe and soil. However, it is very difficult to quantitatively determine the real contact conditions between the two. New technology for soil–pipe interaction measurement is still scarce and requires further development. Only indirect methods are available for practical measurement of soil–pipe interaction, and engineering judgment is required for the application of those measurements. In this study, a simple test method was applied to obtain the frictional properties of the most popular lubricants in the Taiwan area. Those frictional properties were used for jacking force estimation and numerical analysis of soil–pipe interaction for linear and curved pipe-jacking. The analyses of jacking force show that reduction in jacking force is closely related to reduction in friction coefficients, and the effect of lubrication is slightly more significant in the case of curved alignment than the case of linear alignment. In addition, a study of a 400-m linear pipe-jacking case in the Taichung Science Park shows overestimation of the jacking force by an empirical formula. It reveals the reduction in pipe-soil contact area induced by over-cutting is significant for pipe-jacking in gravel formations.     

Acceleration generation due to strain localization of saturated clay specimen based on dynamic soil–water coupled finite deformation analysis

In the conventional bifurcation and strain localization analyses of geomaterials, the inertia forces are generally ignored, based on the quasi-static equilibrium equation. Even though a great deal of literature exists on dynamic strain localization analyses, information on acceleration generation during the formation of shear bands has not been emphasized. Inspired by the acoustic emission phenomenon in laboratory tests and the seismic acceleration related to the slippage of faults, a dynamic soil–water coupled strain localization analysis is performed in the present paper on a saturated rectangular clay specimen subjected to constant cell pressure under plane strain conditions, employing the SYS Cam–clay model as the elasto-plastic constitutive model for the soil skeleton. An initial geometrical imperfection was introduced to the specimen to trigger one single shear band, and the following results were found: (1) Two types of oscillation occurred within the specimen during acceleration when the specimen was subjected to compression deformation at a constant rate, namely, (a) one caused by the sudden external compression and (b) the second induced by the formation of strain localization/a shear band. With the occurrence of the shear band, if, for example, the vertical rate was equivalent to about 10 cm/s, the accelerations that occurred within the specimen were in the order of several thousand gal, which is similar to those measured during earthquakes; (2) The effects of the time increment, the mesh division, the initial confining pressure, the OCR and the stress-control loading on the generated acceleration in (b) were investigated in detail. It was found that under stress control, even though the formation of the shear band was similar to that under displacement control, the induced acceleration behaved quite differently.     

Dynamic analysis of liquid storage tank under blast using coupled Euler–Lagrange formulation

A growing number of terror attacks all over the world have become a threat to the human civilization. In the last two decades, bomb blasts in crowded business areas, underground railway stations and busy roads have taken numerous lives and destroyed properties in different parts of the world. However, blast response of many important civil infrastructures has still not been well understood due to the complexities in their material behavior, loading and higher nonlinearities. One such example of important civil infrastructure is liquid storage tanks which are undividable parts of any society for storage of water, milk, liquid petroleum, chemicals in industries etc. Blast loading on liquid storage structures may lead to disaster due to water and milk crisis, health hazard owing to the spread of chemicals and fire hazard due to the spread of liquid fuel. Hence, understanding the dynamic behavior of liquid storage structures under blast loading through numerical simulations is of utmost importance. In the present study, three dimensional (3D) finite element (FE) simulations of a steel water storage tank for different tank aspect ratios, percentages of water stored in the tank, tank wall thicknesses, boundary conditions at the bottom of the tank and magnitudes of blast loading have been performed using the FE software Abaqus. The coupled Euler–Lagrange (CEL) formulation in Abaqus has been adopted herein which has the advantage of considering the coupling of structural mechanics and fluid mechanics fundamental equations. The maximum hoop stress and shear stress in the tank wall, the water sloshing heights in tanks and the energy response of the tanks have been studied. It is observed that stresses and liquid sloshing heights in the tank increase with decreasing scaled distance of the explosive material and increasing aspect ratio, i.e. height to radius ratio.