Interface Direct Shear Research Articles

Role of particle shape on the shear strength of sand-GCL interfaces under dry and wet conditions

Interface shear strength of geosynthetic clay liners (GCL) with the sand particles is predominantly influenced by the surface characteristics of the GCL, size and shape of the sand particles and their interaction mechanisms. This study brings out the quantitative effects of particle shape on the interaction mechanisms and shear strength of GCL-sand interfaces. Interface direct shear tests are conducted on GCL in contact with a natural sand and a manufactured sand of identical gradation, eliminating the particle size effects. Results showed that manufactured sand provides effective particle-fiber interlocking compared to river sand, due to the favorable shape of its grains. Further, the role of particle shape on the hydration of GCL is investigated through interface shear tests on GCL-sand interfaces at different water contents. Bentonite hydration is found to be less in tests with manufactured sand, leading to better interface shear strength. Grain shape parameters of sands, surface changes related to hydration and particle entrapment in GCL are quantified through image analysis on sands and tested GCL surfaces. It is observed that the manufactured sand provides higher interface shear strength and causes lesser hydration related damages to GCL, owing to its angular particles and low permeability.

A Review of Sand–Clay Mixture and Soil–Structure Interface Direct Shear Test

Natural soils are usually heterogeneous and characterized with complex microstructures. Sand–clay mixtures are often used as simplified soils to investigate the mechanical properties of soils with various compositions (from clayey to sandy soils) in the laboratory. Performing laboratory tests on a sand–clay mixture with definite clay fraction can provide information to understand the simplified soils’ mechanical behavior and better predict natural soils’ behavior at the engineering scale. This paper reviews previous investigations on sand–clay mixture and soil–structure interface direct shear test. It finds that even though there are many investigations on sand–clay mixtures and soil–structure interfaces that consider pure sand or pure clay, limited data on the mechanical behavior of the interface between sand–clay mixture and structure materials are available. Knowledge is missing on how the clay content influences the mechanical behavior of interface and how the soil particles’ arrangement changes as the clay content increases. Further study should be performed to investigate the interface in terms of a reconstituted sand–clay mixture and structure by interface direct shear test, to highlight the influence of clay fraction on the interface response, under various loading conditions.

Interface Direct Shear Tests on JEZ-1 Mars Regolith Simulant

The mechanical behaviors of Martian regolith-structure interfaces are of great significance for the design of rover, development of excavation tools, and construction of infrastructure in Mars exploration. This paper presents an experimental investigation on the properties of a Martian regolith simulant (JEZ-1) through one-dimensional oedometer test, direct shear test, and interface direct shear tests between JEZ-1 and steel plates with different roughness. Oedometer result reveals that the compression and swelling indexes of the JEZ-1 are quite low, thus it is a less compressible and lower swelling soil. The cohesion and adhesion of JEZ-1 are lower than 5 kPa. The values of the internal friction angle range from 39.7° to 40.6°, and the interface friction angles are 16.7° to 36.2° for the smooth and rough interface. Furthermore, the direct shear and interface direct shear results indicate that the interface friction angles are lower than the internal friction angles of JEZ-1 and increase close to the internal friction angles with increasing interface roughness.

Application of disturbed state concept for load-transfer modeling of recoverable anchors in layer soils

As a temporary anchorage technique, recoverable anchors have been widely adopted in excavation supporting and underground mining for their unique economic and social merits. The current study attempts to investigate the load-transfer behavior of recoverable anchors in layer soils. The interaction between soil and grout was characterized by a new developed disturbed state concept (DSC) model, in which the interface normal stress was considered. The good agreement between predictions and experimental results from element pullout tests and interface direct shear tests validated the extensive applicability of the DSC model. A theoretical modeling framework for load-transfer behavior of recoverable anchors in layer soils was proposed based on finite difference method, in which the soil-grout interactions were simulated by the DSC model. 3D finite element (FE) models were developed to simulate the pullout behavior of recoverable anchors. The results obtained from theoretical modeling and FE simulations were discussed in detail. Comparisons with numerical simulations and in-situ test data have led to the validation of the theoretical modeling framework. Finally, parametric studies were presented. Application of this work is to evaluate the pullout capacity of recoverable anchors, which can provide theoretical guidance for the design practice of anchoring engineering.

A Procedure to Prepare Sand–Clay Mixture Samples for Soil–Structure Interface Direct Shear Tests

A large number of experimental studies on sand–clay mixtures are well documented in the literature; however, the preparation protocol is rarely clearly detailed or varies a lot according to the authors. Variations in the preparation technique obviously increases the challenge of comparing different test results. As a consequence, sample preparation for sand–clay mixtures should be kept as constant as possible to ensure homogeneity and uniformity of samples and limit result variability. This paper develops a detailed procedure on how to prepare sand–clay samples for interface direct shear tests. Sand–clay mixtures are prepared with Fontainebleau sand, kaolinite clay and distilled water by the S1 (sand–water–clay) protocol. The uniformity of the reconstituted specimens is assessed by measuring the water content and density on three slices from the top to the bottom across the specimens. The repeatability of the samples is checked with oedometer and interface direct shear tests. This sample preparation procedure can be used for preparing sand–clay mixture for interface direct shear tests to investigate the influence of clay content or other effects (e.g., temperature) on the mechanical behavior of soil–structure interface. It has demonstrated great performance in preparing samples with good homogeneity and shape, compared to other traditional reconstitution techniques. With the sample preparation procedure, we can obtain repeatable test results as well.

A shear damage model of the interface between soil and sulfate-corroded concrete

In order to investigate the mechanical properties of the interface between sulfate-corroded concrete piles and soil, a corrosion shear damage model and a method to determine the model parameters were proposed based on statistical damage theory. Assuming that the corrosion damage of the interface obeys Weibull random distribution, a damage model is established, which contains only six parameters. By fitting curves, the model parameters are obtained from the interface direct shear test. The shear damage model can not only predict the shear deformation behaviors, but also consider the effects of normal stress and corrosion time on the shear properties of the interface after corrosion. The results show that the shear stress-displacement relationships are significantly affected by normal stress and corrosion time. The peak shear stress increases with normal stress, and the corresponding peak shear displacement also increases. The longer the corrosion time is, the less obvious the shear softening phenomenon of soil-concrete interface is, and as the corrosion time reaches a threshold level, the softening phenomenon of shear stress-displacement relationship changes into weak softening. Finally, the rationality and feasibility of the proposed model are verified by comparing the theoretical curves with the experimental curves.

Axial Pullout Resistance and Interface Direct Shear Properties of Geogrids in Pond Ash

Presently, pond ash is accumulated in large quantities in thermal power plants. There is potential for large-volume utilization of pond ash as a fill material. Applications involving mechanical stabilization of fills constructed with geogrid-reinforced pond ash is explored in the study. A systematic experimental program was carried out to evaluate the interface direct shear strength and axial pullout resistances of four to eight different uniaxial polyester geogrids embedded in pond ash. Geogrids of varying tensile strengths and opening area ratios were considered. No significant difference in the interfacial shear strengths was observed among the four different geogrids tested. Based on the interface direct shear strengths at peak and critical states, the efficiencies of geogrids were found to range from 62 to 83%. The axial pullout resistances of geogrids in pond ash were found to be high for grids with high tensile strength. Finally, based on extensive pullout test results, empirical equations were fitted to estimate the axial pullout resistance of uniaxial geogrids embedded in pond ash corresponding to two front-end axial pullout displacements of 30 mm and 60 mm. The proposed equations were found to agree very closely with the experimental results (R2 = 0.95).

Failure mechanisms of geosynthetic clay liner and textured geomembrane composite systems

The objective of this study was to evaluate shear behavior and failure mechanisms of composite systems comprised of a geosynthetic clay liner (GCL) and textured geomembrane (GMX). Internal and interface direct shear tests were performed at normal stresses ranging from 100 kPa to 2000 kPa on eight different GCL/GMX composite systems. These composite systems were selected to assess the effects of (i) GCL peel strength, (ii) geotextile type, (iii) geotextile mass per area, and (iv) GMX spike density. Three failure modes were observed for the composite systems: complete interface failure, partial interface/internal failure, and complete internal failure. Increasing normal stress transitioned the failure mode from complete interface to partial interface/internal to complete internal failure. The peak critical shear strength of GCL/GMX composite systems increased with an increase in GMX spike density. However, the effect of geotextile type and mass per area more profoundly influenced peak critical shear strength at normal stress > 500 kPa, whereby an increase in geotextile mass per area enhanced interlocking between a non-woven geotextile and GMX. Peel strength of a GCL only influenced the GCL/GMX critical shear strength when the failure mode was complete internal failure.

Cyclic thermomechanical response of fine-grained soil−concrete interface for energy piles applications

Understanding the behaviour of soil−structure interfaces is critical for addressing the analysis and design of energy geostructures. In this study, the interface failure mechanism of energy piles (where a shear band is detached from the surrounding soil that behaves under oedometric conditions) is experimentally analysed in the laboratory for saturated conditions. The choice of material (clayey soil and concrete), temperature range, and stress level is based on conditions that are likely to be encountered in practice. Specifically, cyclic thermal tests under constant vertical effective stress in oedometric conditions as well as constant normal stiffness (CNS) interface direct shear tests (in which samples have been subjected to thermal cycles between 10 and 40 °C) are presented. From a practical perspective, the results show very low volumetric strain variations and negligible effects on shear strength. The volumetric aspects do not appear to have significant impact on the shear resistance of the interfaces against cyclic thermal loads. Fundamental insight on the effects of thermal cycles on the concrete−soil interface behaviour that are relevant to energy piles are presented. In addition, the proposed interpretation procedure provides a basis for the standardization of thermomechanical testing in geotechnical engineering.

Relating shaft friction of buried piles and CPT resistance in clayey sands

This paper examines factors controlling the ultimate shaft friction developed on buried piles in normally consolidated clay–sand mixtures and explores the relationship between this friction and the cone penetration test (CPT) end resistance. Results from tension load tests on buried piles in a laboratory pressure chamber and geotechnical centrifuge are presented. Variable rate CPTs combined with Rowe cell, undrained simple shear and interface direct shear tests are used to characterise the mixtures. It is shown that the measured drained CPT end resistances could be predicted using parameters assessed from the laboratory tests and a simple expression derived from cavity expansion theory in an elastic Mohr–Coulomb soil. The tension pile tests indicate how changes in radial effective stresses during loading can be inferred from interface shear tests and these combined with the cavity expansion analysis allow derivation of a relationship between shaft friction (τf) and CPT end resistance (qt). This expression reveals the significant effects on the qt/τf(= βc) ratio of soil stiffness, stress level, dilation and drainage during cone penetration and is shown to be consistent with a recently proposed empirical formula for bored piles.

Effect of geosynthetic reinforcement on the bearing capacity of strip footing on sandy soil

Due to the increasing presence of problematic soils, expansive clays and highly compressive sand engineers are using a verity of soil improvement techniques to treat such soils. While geosynthetics are extensively used for improving soil characteristics in roads, pavements and embankments, it can also be used to increase the lack of bearing capacity of residential housing or lightweight structures constructed on sandy soils. In order to simulate site conditions in the laboratory environment, a laboratory-scale testing platform has been manufactured to assess the behaviour of geosynthetics reinforced and un-reinforced strip footing. The first group of tests were performed on the unreinforced compacted sandy soils with different densities where the other group of tests were carried out in the soil that has been reinforced individually with three different types of geosynthetic materials having distinct tensile strengths. Furthermore, interface direct shear tests and consolidated undrained triaxial tests have been carried out to determine the shear parameters which is directly influencing the bearing capacity a strip footing. Geosynthetic reinforcement has considerably enhanced the mechanical behaviour of sandy soil in regarding the type of geosynthetic. Furthermore, it was observed that coir geosynthetic has provided increased interfacial friction when compared to other geosynthetic types and improved bearing capacity. Moreover, the adopted testing method found to represent well the behaviour of such materials in the laboratory environment.

Laboratory investigation of unsaturated clayey soil-geomembrane interface behavior

Suction-controlled interface direct shear tests were conducted on textured and smooth HDPE geomembrane counterfaces in contact with lean clay. Soil samples were compacted wet of optimum to simulate placement conditions in a composite liner. Tests on saturated samples and soil only were conducted for comparison. Additionally, limited testing was conducted to study the effect of shearing rate on the results. Results reveal that matric suction provided increased shearing resistance, compared to the saturated case, for the textured and smooth geomembrane interfaces, and the extended Mohr-Coulomb envelope provided a good model for geomembrane interface strength. However, strength increases were relatively small compared to soil only, particularly for the smooth interface. Total and water volume changes during shearing were significantly different for unsaturated and saturated conditions. Water volume changes during shearing in saturated soil and interfaces corresponded directly to volume change tendencies during shearing; however, for unsaturated soils this was not the case. Shearing displacement rate was observed to have a profound effect on the shearing resistance of textured geomembranes but had little apparent influence on the smooth geomembrane. Results of this study provide great insight into the unsaturated shearing behavior of clay-geomembrane interfaces and important data for development of constitutive models.

Laboratory investigation of boundary effect on pressure-settlement behavior of foundation soil with limited thickness involving geosynthetics

Plate loading tests were conducted to investigate the effect of a bottom boundary condition on the pressure-settlement behavior of a footing on sand with a limited thickness involving geosynthetics. Seven boundary materials including geosynthetics were used to create different boundary conditions at the bottom of the sand. Interface direct shear tests were conducted first to determine the interface friction angles between these boundary materials and sand, followed by plate loading tests to determine their pressure-settlement curves. Test results show that the sand with a limited thickness by a rigid bottom boundary had a higher bearing capacity than that with a larger thickness. The ultimate bearing capacity of the footing on the sand with a limited thickness generally increased with the increase of the interface friction angle. Geosynthetics provided better lateral restraint than other materials. An equation was developed to describe the relationship of the bearing capacity ratio of the sand with a limited thickness to that with a large thickness versus the soil thickness and the interface interaction coefficient. The effect of the boundary material on the back-calculated modulus of the sand was also evaluated.

A simple model for sand–structure interface behaviour

This paper deals with the modelling of sand–structure interface behaviour under monotonic loading. In particular, the importance of the stress–dilatancy relationship is highlighted since volumetric behaviour strongly characterises the variation of the normal stress in constant normal stiffness direct shear tests. The procedure for the calibration of constitutive parameters is shown and the model is validated by comparison with different sets of sand–aluminium interface direct shear tests.

Multiscale modeling for analyzing slip weakening at material interfaces

A multiscale framework is proposed for analyzing slip weakening at material interfaces. In the proposed model, discrete granular assemblies are attached to Gauss integration points to capture micro-structural characteristics of granular material, which furnishes the multiscale constitutive formulation. Interface shear slip is performed via penalty method and elasto-plastic decomposition, which formulates the frictional contact relationship. Furthermore, both linear and non-linear interface models are provided to examine slip weakening behavior. In the numerical implementation, both the resulting multiscale constitutive formulation and the frictional contact relationship, are implicitly embedded in conventional continuum-based finite element method (FEM) for solution. The multiscale framework is verified using an interface direct shear test, which shows good agreement between the analytical and numerical results. Cross-scale analyses are performed based on the proposed multiscale framework, which comprises mesh dependency, a macro-micro slip-weakening mechanism and staged responses. The interplay between interface slip weakening and material strain localization is successfully captured, by presenting the global and local responses during shearing where fabric anisotropy, coordination number, particle rotation, void ratio and deviatoric strain are considered.

Sand–concrete interface response: The role of surface texture and confinement conditions

Sand–concrete interface direct shear tests were used to investigate the effects of surface roughness, surface waviness, mean sand diameter and relative density on interface strength and behavior under different confinement conditions. Extreme concrete surface textures, including smooth, rough and rough–wavy textures, were reproduced. Surface plowing was assessed via image analysis, laser scanning and extended multifocal micrographs. The experimental results showed that smooth concrete surfaces exhibited high values of interfacial–to–internal friction angle ratios, ranging 88–90%, due to the angular shape of sand particles. The rough concrete surfaces generated higher interface strength than smooth concrete surfaces; however, the interface strength was still inferior to the surrounding sand strength. Surface plowing, which identified a mixed shear plane at the sand–concrete interface, was developed as particles were detached from the surface, thus inhibiting the interface friction angle from reaching the sand friction angle. Higher sand–concrete interface strength was achieved as surface waviness increased, and interface friction angles greater than the surrounding sand friction angle were reached. Under a constant normal stiffness condition, significantly high interface strength is achieved due to the increase of the current normal stress, which was directly influenced by the initial normal stress, stiffness, surface roughness, mean sand diameter and relative density; surface waviness did not have a marked effect on the normal stress variation. Based on these results, multiple regressions were proposed to estimate the sand–concrete interface strength by the interfacial–to–internal friction angle ratio and the effect of the constant normal stiffness condition.

Analysis of sand – woven geotextile interface shear behavior using discrete element method (DEM)

The interaction between soil and geotextile is essential for the performance of reinforced soil. This study reveals the microscopic mechanism of interface shear between sand and geotextile based on the discrete element method (DEM). The surface characteristics of geotextile are simulated by overlapped particles. The micromechanical parameters of sand, geotextile, and interface are calibrated effectively using laboratory test results. Three types of shear tests on the sand–geotextile interface are simulated; namely, interface direct shear test (IDST), double-sided interface shear test (D_IST), and interface direct shear test with periodic boundary (PBST). For IDST, the results show that the thickness of shear band is 2.4∼3.0 times the average particle diameter (D50); the contact force, percentage of sliding contact, and contact normal anisotropy inside the shear band are larger than those outside the shear band, whereas the coordination number is smaller inside the shear band. The mechanical response of D_IST is similar to that of IDST. However, D_IST has a shear band thickness of 3.0D50, and greater coordination number, percentage of sliding contact, and contact normal anisotropy. The results of PBST indicate that the peak stress and the shear band no longer appear without boundary constraint and the contact distribution is uniform.

Influence of thermal cycles on the deformation of soil-pile interface in energy piles

Energy piles are double purpose foundation elements used both for transferring loads to the soil and temperature regulation in buildings. The response of the pile-soil interface is influenced by daily and seasonal temperature variations. In order to assess the impact of thermal cycles on the mobilization of shear strength in energy piles, a series of saturated soil-concrete interface direct shear tests were performed in the laboratory for different temperature gradients with a new interface direct shear device adapted for thermomechanical loading. As natural soils are very complex due to a high variability of mineralogy and anisotropy, silica and carbonate sands were chosen in this study. Those sands are considered as the main types of sandy soils commonly met in geotechnics. The experimental campaign is divided in two parts: (i) Concrete-soil direct shear tests at 13°C (constant temperature) to be used as a reference (ii) Concrete-soil direct shear tests after 10 temperature cycles with a gradient ΔT=10°C, under submerged conditions. For these two types of soils, realistic temperature cycles applied between 8 and 18°C cause the overall low contraction of the samples. However the interface friction angles are not significantly modified before and after the temperature cycles. Even if the vertical strains of soils are cumulative along temperature cycles, soil’s strains and friction angle changes are relatively negligible for the temperatures and water content tested, which support the low impact of temperature cycles on the deformation of soil concrete foundation under submerged conditions. These experimental results bring new features which will be implemented in numerical models to study the long-term use of energy piles.

Discrete element modeling of soil-structure interface behavior under cyclic loading

The cyclic shear behavior of the interface between soil and structure at both the macro and the micro level is investigated by interface direct shear tests under constant normal stiffness condition using discrete element modeling. The simulation results are validated qualitatively by the corresponding experiment. The influence of the initial state of the specimen (i.e. soil density and normal stress) on the cyclic behavior is systematically discussed. Moreover, the cyclic accumulative deformation of the interface is carefully studied in the view of the void ratio and the correlation between the final deformations under cyclic and monotonic loading is explored.

Large-Scale Combination Direct Shear/Simple Shear Device for Tire-Derived Aggregate

Abstract This paper describes a novel large-scale device capable of performing both direct shear and simple shear tests to evaluate shear deformation and strength properties of Type B tire-derived aggregate (TDA). The device consists of stacked tubular steel members that can be locked as upper and lower rigid sections to displace relative to one another in direct shear or pinned at the ends to translate in simple shear. For both configurations, the TDA specimen has a length of 3,048 mm, a width of 1,220 mm, and an initial height up to 1,830 mm. The upper rigid section of the device can also be used to conduct interface direct shear tests. Vertical stress is applied to the top surface of the specimen using deadweights and horizontal shearing force is applied using two hydraulic actuators in displacement-control mode. Typical results from internal direct shear, concrete interface direct shear, and cyclic simple shear tests are presented. In direct shear mode, the device allows for mobilization of peak shear strength and, in simple shear mode, for evaluation of shear stiffness and damping ratio under large strain conditions for TDA with large particle size.