Shear Behavior Of Soil Research Articles

The effect of relative density, granularity and size of geogrid apertures on the shear strength of the soil/geogrid interface

The increasing use of geogrid in various geotechnical projects has made the evaluation of the shear behavior of soil reinforced with geogrid become particularly important. In this article, a series of large-scale direct shear tests have been performed on sand and gravel samples reinforced with geogrid. The purpose of the experiments was to investigate the impact of the geogrid mesh size and the relative density of the samples on the shear strength coefficient of the interface between soil and geogrid. In this study, 5 geogrids with different mesh sizes and one type of geotextile were used. According to the results, the average shear strength coefficient of sand and gravel samples reinforced with geogrid for different normal stresses and different relative densities was obtained between 0.72 and 0.94. As the relative density increases, the interface shear strength coefficient decreases, this means that the denser the sand, the more the shear strength of the sand/geogrid interface decreases. Based on the results, it was found that the contribution of particle interlocking in the shear resistance of the sand/geogrid interface is particularly important, so that the shear resistance coefficient of the interface increases with the increase in the size of the geogrid mesh.

Case Study: Slope Stability Assessment Considering 3D Nonlinear Shear Strength

In this paper, factor of safety (FOS) considering three-dimensional (3D) and nonlinear shear strength of geomaterials is formulated based on the modified spatial mobilized plane (MSMP) model. The MSMP model has the desirable features of considering 3D strength and the nonlinear shear behavior of soils, compared with the widely used Mohr-Coulomb (M-C) model. The MSMP model is developed from the spatial mobilized plane model by relating the internal friction angle to the mean effective stress within the framework of critical state soil mechanics. Based on the developed MSMP model and the geometric relationships in the mobilized effective normal-shear stress plane, the nonlinear 3D FOS is defined as the ratio of mobilized shear strength to shear stress. The developed nonlinear 3D FOS is applied to slope parametric and case studies. The parametric studies show significant differences between the nonlinear 3D FOS by the MSMP model and the traditional linear two-dimensional (2D) FOS by the M-C model. The case study shows that the MSMP model and nonlinear 3D FOS can better capture the developed failure slope zone than the M-C model and linear 2D FOS.

Influence of the thermal effect on quasi-static shear characteristics of calcareous soil: an experimental study

In principle, the mechanical properties of soil particles are irreversibly changed after particles are subjected to heating. Accordingly, this study performed ring-shear tests on calcareous sand samples subjected to high temperatures to qualitatively investigate the influence exerted by the degradation of the calcareous sand, caused by the thermal effect, on the large displacement shear characteristics of the samples. The effects of the shear velocity and normal stress on the quasi-static shear behavior of the calcareous sand samples were analyzed. The influence of the thermal effect on the quasi-static shear flow behavior of the samples is primarily reflected in the change in the particle mineral composition, particle hardness, and sample density. These variations result in changes in the shear strength, residual shear stress, macroscopic friction coefficient, and other shear characteristics of the calcareous sand samples. Both the shear velocity and the high temperature affect the fluctuation amplitude of the residual shear stress. The results have great theoretical and practical significance in terms of explaining the instability mechanism of a slope. Moreover, a feasible and effective technique is proposed to investigate the large-displacement shear behavior of soil subjected to the thermal effect exerted by a long-runout landslide.

Thermomechanical response of kaolin clay–concrete interface in the context of energy geostructures

The analysis and design of energy geostructures are mainly characterised by the mechanical behaviour of the soil–structure interface in non-isothermal conditions. In this study, direct shear tests are conducted to investigate the shear behaviour of soil and soil–structure interface in the practical temperature range of energy geostructures (i.e., 8–45 °C). The interface in this study is formed of kaolin in contact with concrete specimens with different roughness. Tests are performed on normally consolidated and overconsolidated interfaces following the unloading/reloading paths to better understand the impact of thermal strain on the interface behaviour. The volumetric response of the interface is observed to be highly influenced by the thermal strains experienced during heating/cooling. The soil stress level and the most recent soil stress history are identified as the primary determinants of thermally induced changes in interface shear strength. For normally consolidated interfaces, the temperature increase led to higher adhesion and slightly lower friction angle, whereas higher adhesion and identical friction angles were found for tests conducted on cooled specimens. Temperature does not seem to affect the shear strength of overconsolidated interfaces. Finally, a conceptual understanding of the temperature effect on interface shear behaviour is provided by analysing data from the literature.

Influence of Block form on the Shear Behaviour of Soft Soil–Rock Mixtures by 3D Block Modelling Approaches

The influence of block forms on the shear behaviour of soil–rock mixtures with soft blocks (soft S–RMs) can be efficiently investigated by the discrete element method (DEM) on the basis of accurate 3D models accounting for the block breakage. This paper proposes a novel modelling approach, based on the spherical harmonics series, for the generation of 3D block geometries with different forms but same convexity and angularity. An already existing non-overlapping modelling approach was improved, characterized by a reduced computational cost, for the set-up of 3D block DEM models accounting for the block breakage. A number of soft S–RM DEM samples, subjected to numerical direct shear tests, were generated to analyze the influence of block forms and volumetric block proportion VBP on the mesoscopic and macroscopic behaviours. The results showed that the breakage degree is maximum for the spheroidal blocks, followed by the oblate, prolate and blade ones, due to the combined influence of the block frictional sliding and rotation. The shear strength of soft S–RMs is mainly controlled by the block interlocking and breakage, being maximum in the case of spheroidal block samples when the applied normal stress is low and in the case of prolate and blade ones for a high normal stress. It was found that a nonlinear Mohr–Coulomb criterion can provide a good description of the shear strength envelope of soft S–RMs. Soft S–RMs are characterized by a higher friction angle if composed by spheroidal and prolate blocks when the VBP is 40%, due to their elevated block interlocking, and in the case of prolate and blade blocks when the VBP is 60% at the higher normal stress, due to their lower block breakage degree.

Experimental Investigation and Mapping of Index and Shear Behavior of Soils a Case in Gimbichu Town, Ethiopia

Objectives: To study experimental investigation on index and engineering properties of fine-grained soils by conducting laboratory tests and to prepare a soil spatial map using ArcGIS software of Gimbichu town, Ethiopia. Methods: Hence, ten test pits were selected according to the variation of the soil and the distribution of the dwellings. The soil samples were collected by direct manual excavated to 1.5m and 3.0m depth on which both laboratory and field tests were conducted for index and shear properties. Findings: Index properties revealed that soils in the study area are mostly silt soils with high plasticity and partly low plasticity. It is indicated that the soils are medium to very stiff with unconfined compressive strength of 53.70 to 216.40kPa and undrained shear strength of 26.67 to 108.20 kPa. Permeability and consolidation investigation results presented soils in the town are silt group. The spatial soil property map is created for experimentally determined results at 1.50m and 3.0m depths using ArcGIS software to retain soil properties in order to earn time and cost of the investigation in the field and laboratory. These maps are required for recognizing, identifying, and classification of soil categories within delineated parts of the current study town. Novelty: Investigation and ArcGIS spatial mapping for soil properties are essential for future boosting of the design and construction buildings of this town that was not applied before in investigation lagged areas like Gimbichu town. Keywords: ArcGIS Mapping; Experimental study; Index properties; Shear parameters; Soil class

Effect of straw reinforcement on the shearing and creep behaviours of Quaternary loess

In addition to the shearing behavior of soil, the creep character is also considered crucial in determining the long-term shear strength. This especially holds true for the loess that possesses the metastable microstructure and is prone to landslide hazards. This study explored the potential application of straw reinforcement to enhance the shearing and creep properties of the Quaternary loess. The mechanism responsible for the straw reinforcement to elevate the peak shear strength was revealed. Furthermore, three creep characters, namely attenuating creep, non-attenuating creep, and viscous flow were identified in this study. The unreinforced and reinforced specimen behaved in a different manner under identical shear stress ratio condition. The reinforced specimen was superior in limiting the particle relative movement within the shear plane than the unreinforced specimen. The chain reaction of interparticle contact loss, accompanied with excessive viscous displacement, rapid weakening of creep resistance, and eventually accelerated creep displacement, provided an evidence for the formation mechanism of slow-moving landslide. The long-term shear strength using the isochronal stress–strain relationship may be used for optimising the design of high-fill embankment works.

Shear Behavior of Soil–Rock Mixture Composed of Diorite-Porphyrite Considering Weathering Sequence

Abstract Due to the weathering process, diorite-porphyrite dikes break up into a soil–rock mixture (SRM), which is crucial to the stability of dams and reservoirs that are under frequent fluctuatio...

Behavior of Weathered Soil under Combined Undrained Cyclic-Monotonic Loading

Abstract Liquefied soils are considered as soils devoid of any strength or having only limited strength. Post-liquefaction shear behavior of soil before the drainage of excess pore pressure is impo...

Shear behaviour of sand-concrete interface with side post-grouting considering the unloading effect

Side post-grouting bored-pile foundations are widely used in geotechnical engineering. However, few studies have focused on analyzing the shear behaviour of soil and concrete while considering the grouting process. A total of 48 groups of self-developed, large-scale direct shear experiments were conducted to investigate the shear behaviour of sand-concrete interface with side-grouting, focusing on the effect of soil stress unloading and the on-site roughness measurements of bored pile. The influence of the grouting volume V, unloading rate α and interface roughness R on the shear behaviour are discussed, and the grouting modes and shear band deformation are investigated. The experimental results indicated that the grouting volume has a limited effect on improving the shear strength, and an optimal grout quantity will exist in post-grouting engineering. In addition, the unloading has a non-negligible influence on the grouting modes.

Effect of Different Modes of Lateral Boundary Constraints of the Direct Simple Shear (DSS) Device under Monotonic and Cyclic Shear Loading

Abstract The direct simple shear (DSS) device is commonly employed to characterize the shear behavior of soil while representing a plane strain condition. In DSS devices that use cylindrical specimens, the plane strain condition is mimicked by constraining the lateral boundaries of the specimen against radial deformations during consolidation and shear loading. The current test standard recommends using either wire-reinforced rubber membrane or unreinforced rubber membrane enclosed with stacked rigid rings as suitable modes of confinement to constrain the lateral boundaries of DSS test specimens. Only limited studies have been performed to assess the effects arising because of these different ways of lateral boundary constraints on the test results, particularly when DSS tests are conducted at relatively higher vertical effective confining stress (σ′v0) levels. An experimental program was undertaken to study the effect of lateral boundary constraint mode during constant-volume monotonic and cyclic DSS tests. The constant-volume tests were conducted on reconstituted cylindrical DSS specimens prepared from a natural silty soil under the following three modes of lateral boundary constraints: (a) steel wire–reinforced rubber membrane only (Mode 1); (b) steel wire–reinforced rubber membrane enclosed with a set of thin, low-friction stacked rigid rings (Mode 2); and (c) unreinforced rubber membrane enclosed with a set of thin, low-friction stacked rigid rings (Mode 3). The findings from these tests, conducted on specimens initially consolidated to σ′v0 level up to 900 kPa, indicate that there was no significant difference in the shear response derived from the three cases of lateral boundary constraints. This suggests that the commonly used approach of simply confining the DSS test specimen using steel wire–reinforced rubber membrane alone (i.e., Mode 1) would be effective and adequate for use in monotonic and cyclic direct simple shear testing, for σ′v0 ≤ 900 kPa.

Influence of stress history, strain rate and end effects on undrained shear behaviour and strain localization of laterite soil

ABSTRACT Recognizing the abundant use of lateritic soils in the construction of embankments and their susceptibility towards extreme erosion, it is necessary to explore the influence of stress history and strain rate on their undrained shear behaviour. The mechanism of development of localized deformation and failure of soil mass are equally important for understanding the stability of laterite soils. Moreover, the use of porous stones in conventional triaxial testing for drainage to investigate the undrained shear behaviour of soils leads to the development of shear stresses near the ends and thereby influences the mechanical response of the soil. In the current research, the effect of stress history, strain rate and boundary effects on the shear strength behaviour and strain localization patterns of naturally available laterite soil is explored. The effect of end boundaries on the initiation and propagation of localized deformations of soil have been also evaluated in this study.

Shear Band Characterization of Clayey Soils with Particle Image Velocimetry

Identifying the spatial distribution of deformation and shear band characteristics is important for accurately modeling soil behavior and ensuring the safety of nearby geotechnical structures. However, most research on the shear behavior of soils has focused on granular soil and clay-rich rocks, with little focus on clayey soil, and the entire shearing process from the initial state to failure has not been observed. This study evaluated the spatial distribution and evolution of deformation in clayey soils from the initial state to the post-failure state and the shear band characteristics. Plane strain tests were performed on normally consolidated and over-consolidated clay specimens, and digital images were captured through a transparent side wall for particle image velocimetry (PIV) analysis. PIV was performed to evaluate the displacement and deformation of soil particles. The results show that the shear-strain behaviors of two clays during the shearing process could be divided into four stages: initial, peak, softening, and steady state. Shear bands were observed to form in the softening stage, and the shear band slopes were compared to values in the literature. These results can be used to characterize shear bands in clay as well as predict failure behavior and guide reinforcement at actual sites with soft ground.

Effect of organic content and cement quantity on the shear behavior of artificially cemented soil

Most of the soil in the universe contain organic matter that results on the negative effects on the shear behavior of soil. The objective of this research is to study the effect of organic content and proportion of cement of artificially cemented soil. A compaction and direct shear test without curing period were undertaken on the soil with 6, 11, 16, and 21% organic content. Direct shear test results show that the soil cohesion decrease and internal friction angle slightly increase as increasing of organic content. The direct shear test of artificially cemented soil with 21, 28, 42, and 56 curing time was then performed to investigate the effect of cement quantity on the shear behavior of cemented soil. The cement content was 25, 50, 75, and 100 kg/m3. The more cement quantity added to the soil, cohesion and friction angle of artificially cemented soil improves. There is also improvement of the shear stress due to the increase of cement proportion. Similarly, shear strength of stabilized soil improves inherent with curing period due to the short and long-term pozzolanic reactions.

Quantitative Analysis of Microstructure Properties and their Influence on Macroscale Response

The shear behavior of soils is typically related to the state of the soil in terms of the initial global void ratio and effective confining stress. However, laboratory tests on reconstituted sand specimens have shown that the shear behavior is also dependent upon the specimen preparation method. This paper describes the findings of a series of studies, which quantitatively evaluated the differences in the inherent microstructure of dilatant sand specimens prepared by air pluviation, moist tamping and water deposition. Quantitative measures such as local void ratio distribution, local void ratio distribution entropy and particle orientation entropy were found to be dependent on the preparation method. Microstructure evolution in the sand specimens during triaxial compression testing was also investigated. Measuring global properties of the specimens was shown to mask the complex and evolving internal conditions during shear. The global response was found to be strongly dependent on the shear induced microstructure which in turn was directly influenced by the preparation method dependent inherent microstructure.

Effects of particle sphericity and initial fabric on the shearing behavior of soil–rough structural interface

In this study, the effects of particle sphericity and initial fabric on the shearing behavior of soil-structural interface were analyzed by discrete element method (DEM). Three types of clustered particles were designed to represent irregular particles featuring various sphericities. The extreme porosities of granular materials composed of various clustered particles were affected by particle sphericity. Moreover, five specimens consisting of differently oriented particles were prepared to study the effect of initial fabric. A series of interface shear tests featuring varying interface roughnesses were carried out using three-dimensional (3D) DEM simulations. The macro-response showed that the shear strength of the interface increased as particle sphericity decreased, while stress softening and dilatancy were easily observed during the shearing. From the particle-scale analysis, it was found that the thickness of the localized band was affected by the interface roughness, the normal stress and the initial fabric while independent of the particle sphericity. The thickness generally ranged between 4 and 6 times that of the median particle equivalent diameter. A thicker localized band was formed in the case of rougher interface and in soil composed of inclined placed and randomly placed particles. The coordination number measured in the interface zone and upper zone suggested that the dilation mostly occurs inside the interface zone. Anisotropy was induced by the interface shearing of the initial isotropic specimens. The direction of shear-induced anisotropy correlates with the shearing direction. The evolutions of anisotropies for the anisotropic specimens depend on the initial fabric.

Influence of surface texture on sand–steel interface strength response

The surface texture of the interface material plays a significant role in the shear behaviour of soil–continuum interface. This study investigates the influence of surface texture of steel on the shear behaviour of sand–steel interface using different types of steel counterfaces with distinct texturing patterns. The patterns include concentric circular asperities, square-tiled surfaces with equally spaced individual asperities and ruled ribbed asperities oriented parallel, perpendicular and at an angle to the shear direction. The results show that the texturing pattern of the steel counterface significantly affects the shear strength of the sand–steel interface. The peak and residual interface friction angles for the sand–steel interfaces with different texturing patterns (with identical asperity height and spacing) varied from 26·6° to 37·5° and 14·2° to 28·7°, respectively. Moreover, the surface with ruled ribs/asperities inclined at right angle to the shear direction shows the maximum interface shear strength among all the texturing patterns tested. The findings presented herein are imperative for a realistic assessment of the performance of geotechnical structures involving soil–steel interaction.

Effect of initial pore pressure on undrained shear behaviour of fine-grained gassy soil

Many of the world reserves of fossil fuels are located at various water depths in fine-grained sediment under the seabed. The fine-grained sediment contains relatively large biogas bubbles, which has been posing challenges to the stability of offshore foundations supporting oil and gas platforms. Although fine-grained gassy soil was found to exhibit different undrained shear strengths (cu) by altering the initial pore pressure, ui (relevant to water depth), systematic studies concerning the effect of ui on undrained shear behaviours of the soil are still lacking. This study reports a series of undrained triaxial tests aiming to compare and investigate the responses of reconstituted fine-grained gassy soil with the same consolidation pressure ([Formula: see text]), but at a wide range of varying ui (0–1000 kPa). The shearing-induced excess pore pressure (Δu) in the gassy specimens highly depends on ui. It can be either smaller than that of the saturated specimen with the same [Formula: see text] (due to partial dissipation of Δu into relatively large bubbles at low ui) or larger than that of the saturated specimen (related to collapse of relatively small bubbles at high ui). Consequently, the presence of bubbles had beneficially increased cu at relatively low ui (ui/[Formula: see text] < 0.6), and vice versa. The critical stress ratio of the reconstituted fine-grained gassy soil, however, did not appear to be altered by ui.

Introduction and analysis of a strain-softening damage model for soil–structure interfaces considering shear thickness

A damage strain softening model for predicting the shear behavior of soil–structure interfaces is presented. The damage model, which contains only four parameters (i.e., undamaged shear modulus G′, damage evolution parameters n and m, and the residual shear stress τr), is developed based on Weibull distribution statistical damage theory. By fitting curves, the model parameters are obtained from director simple shear tests. As the shear thickness is usually considered an important factor on soil–structure interface constitutive relations, the shear thickness ratio (η) is introduced to the model to compensate for the influence of the shear thickness. The relationships between the model parameters and the shear thickness ratio η are also analyzed under different levels of normal stress based on data from both direct and simple shear tests. The results show that the undamaged shear modulus G′ increases with increasing normal stress and increasing shear thickness. The shear thickness has a significant effect on the damage evolution parameter n, but the normal stress does not. Neither normal stress nor shear thickness have significant effects on the damage evolution parameter m. The residual shear stress τr increases with increasing normal stress.

Design of a split Hopkinson pressure bar with partial lateral confinement

This paper presents the design of a modified split Hopkinson pressure bar (SHPB) where partial lateral confinement of the specimen is provided by the inertia of a fluid annulus contained in a long steel reservoir. In contrast to unconfined testing, or a constant cell pressure applied before axial loading, lateral restraint is permitted to develop throughout the axial loading: this enables the high-strain-rate shear behaviour of soils to be characterised under conditions which are more representative of buried explosive events. A pressure transducer located in the wall of the reservoir allows lateral stresses to be quantified, and a dispersion-correction technique is used to provide accurate measurements of axial stress and strain. Preliminary numerical modelling is utilised to inform the experimental design, and the capability of the apparatus is demonstrated with specimen results for a dry quartz sand.