Showing papers on "Direct shear test published in 2023"
TL;DR: In this article , a dual-structure shear constitutive model was developed to reveal the full shearing deformation evolution features of geological material, and the macro constitutive relation of rock shear deformation was established by accumulating the micro voids' deformation and solid skeleton deformation.
18 citations
TL;DR: In this paper , the theoretical and numerical analyses of the shear stress distribution in the Shear band were investigated. But the analytical model and results could provide a fundamental basis for stability analysis in geotechnical engineering, and the implication for underground engineering analysis was discussed with a case study of strain rockburst in hard rock.
Abstract: Shear stress concentrations may promote damage and failure processes. Quantities of studies have focused on the direct shear loading test, while the analytical model has not yet been studied in depth. Aiming to fill the knowledge gap, the theoretical and numerical analyses of the shear stress distribution in the shear band were investigated. In order to reflect the variation in the stress state, the differential element method was first used. The shear stress distribution equation was derived from the stress equilibrium, geometric and physical equations. The shear stress distribution was plotted, using the proposed equation. After that, the ratio of yield strength to crack initiation strength was calculated. The analytical model was analyzed with FDEM simulation, and the results were compared with those obtained from the laboratory tests. Using the elastoplastic theory, the damage evolution and process in rock were characterized from laboratory scale. The implication for underground engineering analysis was finally discussed with a case study of strain rockburst in hard rock. The analytical model and results could provide a fundamental basis for stability analysis in geotechnical engineering.
9 citations
TL;DR: In this article , a method for making rock-like samples containing embedded 3D flaw is proposed and a series of shear tests are carried out under different normal stresses, and the test results show that the complex shear stress-shear displacement curve can be divided into four stages.
4 citations
TL;DR: In this paper , the random fractured rock samples were produced with rock-like materials to investigate the fracture propagation and scale effect under compression-shear condition, where the samples were loaded by controlling the compression shear angle to study the mechanical responses and the speckle changes on the samples surface were recorded in real time, and the evolution of strain field was analyzed by digital image processing technology.
Abstract: Fractures and rock blocks are the essential components of rock mass, random fractured rock is the general manifestation of fractured rock mass, which is particularly significant in scale effect. To facilitate the tests, most of the previous studies on fractured rock mass were conducted on regular fractured rocks, which is not conducive to fully revealing the mechanical properties and failure characteristics of fractured rock mass. In this paper, the random fractured rock samples were produced with rock-like materials to investigate the fracture propagation and scale effect under compression-shear condition. Specifically, the samples were loaded by controlling the compression-shear angle to study the mechanical responses. In the test, speckle changes on the samples surface were recorded in real time, and the evolution of strain field was analyzed by digital image processing technology. Then, the internal relations among compression-shear angle, fracture distribution and crack propagation were discussed. Meanwhile, the failure modes of the random fractured samples with different compression-shear angles were summarized to reveal the influence of compression-shear angle on failure mode. Combined with PFC2D, the random fractured rock models of different scales were established to explore the mechanical characteristic variation, and the representative elementary volume of shear modulus was finally determined.
3 citations
TL;DR: In this article , a 3D discrete element method (DEM) model of the direct shear of sand was performed using sphere particles to explore the ability of the rolling resistance linear contact model to reproduce this commonly used test considering real-size particles.
Abstract: This paper deals with the micro and macro behaviors of coarse sand inside a direct shear box during a geotechnical test. A 3D discrete element method (DEM) model of the direct shear of sand was performed using sphere particles to explore the ability of the rolling resistance linear contact model to reproduce this commonly used test considering real-size particles. The focus was on the effect of the interaction of the main contact model parameters and particle size on maximum shear stress, residual shear stress, and sand volume change. The performed model was calibrated and validated with experimental data and followed by sensitive analyses. It is shown that the stress path can be reproduced appropriately. For a high coefficient of friction, the peak shear stress and volume change during the shearing process were mainly affected by increasing the rolling resistance coefficient. However, for a low coefficient of friction, shear stress and volume change were marginally affected by the rolling resistance coefficient. As expected, varying the friction and rolling resistance coefficients was found to have less influence on the residual shear stress.
3 citations
TL;DR: In this article , three particle-scale test setups were developed to measure the tensile, shear, and cyclic shear strength of MICP-treated CaCO3 bonds between glass beads.
Abstract: The particle-scale shear and tensile strength measurements of microbial-induced calcite precipitation (MICP) treatment have been investigated in this paper. Glass beads were used to represent sand particles. Three particle-scale test setups were developed to measure the tensile, shear, and cyclic shear strength of MICP-treated CaCO3 bonds between glass beads. Sporosarcina pasteurii bacterial cells were introduced to precipitate CaCO3 and form cementation bonds between glass beads. The preliminary particle-scale test (Test setup 1) was designed to measure the shear and tensile strength of CaCO3 bonds precipitated between glass beads mounted on optical fiber sensors with known properties. Shear and tension loads were applied to the CaCO3 bonds by the displacement actuators controlling the movement of movable stages. The improved particle-scale test setup (Test setup 2) was developed using a larger and stable reaction chamber, an automated injecting system, and stiff bending elements (instead of optical fibers) that were connected to glass beads to improve measurements. Deflections of the bending elements were measured to calculate the tensile and shear strength of the CaCO3 bonds using the beam theory. The enhanced particle-scale test setup (Test setup 3) was developed to directly measure the shear and tensile forces generated in CaCO3 bonds using load cells and LVDTs to investigate the monotonic and cyclic response of the CaCO3 bonds. For the tests using Test setup 3, the shear and tensile strengths were 378 and 446 kPa, respectively.
3 citations
TL;DR: In this article , a 3D Co-DEM grouted joint shear model, which consists of upper and lower intact rock blocks, 3D real joint surfaces and a grout-filled layer, was developed with the cohesive zone model.
3 citations
TL;DR: In this article , the authors presented the shear-strength parameters under various combinations of principal stress direction α and the intermediate principal stress factor b as obtained through undrained hollow-cylinder torsional shear tests performed on samples of natural granite residual soil.
Abstract: As a result of weathering, the mechanical behavior of granite residual soil differs from that of sedimentary soil. Although the mechanical properties of granite residual soil have been studied extensively, its strength anisotropy is yet to be established. Previous work has revealed the association between the principal stress direction α and soil shear strength, but little is known about how the intermediate principal stress affects the soil strength. This paper presents the shear-strength parameters under various combinations of α and the intermediate principal stress factor b as obtained through undrained hollow-cylinder torsional shear tests performed on samples of natural granite residual soil. The test results confirmed the considerable effect of b on the shear strength and highlighted the differences between the soil studied here and those studied previously. It was found that b affects the undrained strength and mobilized frictional angle (or ultimate stress ratio) differently, with increasing b leading to lower undrained strength but higher frictional angle. In addition, the degrees to which b affects undrained strength and frictional angle are not the same and depend on the α value at which the soil is sheared. Therefore, two parameters are proposed to quantify that difference. This study extends the understanding of the strength anisotropy of granite residual soil and provides data for soil behavior under various values of b.
2 citations
TL;DR: In this paper , a comprehensive study of using xanthan gum, sodium alginate, and gelatin to stabilize collapsible soil was presented, which showed that biopolymers decreased the maximum dry density and increased the optimum water content.
Abstract: This article presents a comprehensive study of using xanthan gum, sodium alginate, and gelatin to stabilize collapsible soil. Modified Proctor, one-dimensional collapse, unconsolidated undrained triaxial, and California bearing ratio (CBR) tests were conducted to estimate the engineering characteristics of the untreated and treated soil. Additionally, X-ray diffraction (XRD) and scanning electron microscopy (SEM) tests were utilized to demonstrate the changes in the microstructure of the treated samples. It was found that biopolymers decreased the maximum dry density and increased the optimum water content. The results also indicated that a 4% content of xanthan gum, sodium alginate, and gelatin significantly reduced the collapse index by 96%, 95%, and 82%, respectively. Shear tests showed that biopolymers slightly reduced the internal friction angle and significantly increased the cohesion intercept, which led to shear strength improvement. The results also indicated that 4% xanthan gum-treated samples, 4% sodium alginate-treated samples, and 4% gelatin-treated samples exhibited higher shear strengths by 145%, 106%, and 73%, respectively, than the untreated sample under the same conditions. The findings also indicated that when the soil was mixed with a 4% concentration of xanthan gum, sodium alginate, and gelatin, the unsoaked CBR value increased by about 185%, 157%, and 141%, respectively. The results of SEM and XRD studies also demonstrated the interaction between the fine-grained particles and the biopolymers.
2 citations
TL;DR: In this paper , a new method for predicting the instability of joints under normal unloading was proposed based on the evolution law of normal deformation energy (Un), tangential deformation energies (Us) and total deformation Energy (U0), which can be used to predict the unloading instability of rock mass using the abrupt change of U0.
Abstract: As a composite material, the stability of rock mass is usually controlled by a joint. During the process of excavation, the normal stress of the joint decreases continuously, and then the shear strength of the joint decreases, which may eventually lead to the instability and failure of rock mass. Previous studies have mainly focused on the shear behavior of joints under constant normal stress, but have rarely considered the unloading of normal stress. In this paper, a direct shear test of joints with different roughness was carried out, in which the shear stress remained unchanged while the normal stress decreased. The strength characteristics of joints were explored, and the deformation and acoustic emission-counting characteristics of joints were analyzed by digital image correlation (DIC) techniques and acoustic emission (AE). A new method for predicting the instability of joints under normal unloading was proposed based on the evolution law of normal deformation energy (Un), tangential deformation energy (Us) and total deformation energy (U0). The results show the following: (1) The unloading amount of normal stress was enlarged for greater initial normal stress and roughness, while it decreased with an increase in initial shear stress. (2) AE events reached their maximum when the normal stress was equal to the failure normal stress, and the b-value fluctuated more frequently in stable development periods under normal unloading conditions. (3) U0 would change with the loading and unloading of stress, and this may be used to predict the unloading instability of rock mass using the abrupt change of U0.
2 citations
TL;DR: In this article , the influence of interface roughness and adhesives on the splitting tensile strength, bi-surface shear strength, and slant-shear strength of the concrete-to-concrete interface were quantitatively studied for 180 specimens.
TL;DR: In this article , a set of 48 cyclic and 12 monotonic large-scale direct shear tests was performed to assess the interface properties of sand-rubber composite along a nonwoven geotextile layer.
Abstract: A set of 48 cyclic and 12 monotonic large-scale direct shear tests was performed to assess the interface properties of sand–rubber composite along a nonwoven geotextile layer. Rubber content, semiamplitude of the shear displacement, and applied normal stress all were varied to determine the cyclic, postcyclic, and monotonic interface response of the composite system under shear loading. The test results show that adding 40% granulated rubber to pure sand caused approximately 50% reduction in the maximum mobilized interface shear stress as the loading cycles progressed. The addition of granulated rubber to the sand decreased both the damping and the shear stiffness of the interface for all values of displacement amplitude and normal stress; in particular, for the energy dissipation, the observations were associated with the higher linearity of the stress–strain relationship when adding rubber, thereby reversing the typical trend of higher damping at smaller strains or displacements. In addition, an increase in the displacement amplitude value yielded a reduction in the secant shear stiffness, but contrarily increased the damping ratio of the geotextile–composite soil interface. An increasing trend of the hardening factor was observed through the initial cycles of loading for the samples containing 40% granulated rubber, which was ascribed to the increased densification capability of the sand–rubber mixture with the progression of the loading cycles; however, this response was not captured for the pure sand–geotextile interface.
TL;DR: In this paper , a series of monotonic shear tests were conducted using a large direct-shear apparatus to evaluate the interface shear strength between a geombrane (GM) and a compacted clay liner (CCL) or a geosynthetic clay lintern (GCL) for landfill stability analysis.
Abstract: The interface shear strength between a geomembrane (GM) and a compacted clay liner (CCL) or a geosynthetic clay liner (GCL) is of great importance for landfill stability analysis. An experimental study of the interface shear behaviour between a smooth GM (GMS) or a textured GM (GMX) and a CCL is presented in this paper. A series of monotonic shear tests was conducted using a large direct-shear apparatus. Peak and residual shear strength parameters were obtained by linear fitting of the experimental data. The shear strength of both GMS/CCL and GMX/CCL interfaces was mainly driven by the normal stress level, while the displacement rate had very little influence on the interface shear strength. The residual shear strength of the GMX/CCL interface was even higher than the peak shear strength of the GMS/CCL interface at all normal stress levels. The GM/CCL interface showed considerably higher shear strength over the GM/GCL interface; the residual strength of the GM/CCL interface was even higher than the peak strength of the GM/GCL interface at all normal stress levels. The results presented in this paper are useful for the preliminary design of landfill composite liner systems.
TL;DR: In this article , a theoretical model was developed to predict the direct shear strength of UHPC which was supposed to be the superposition of those contributions of UHC matrix and fibers.
Abstract: The direct shear performance of UHPC is of great importance for UHPC members in some practical cases, such as shear key and corbels. However, there are seldom available theoretical methods in existing studies for determining the direct shear strength of UHPC. A theoretical model was developed in this study to predict the direct shear strength of UHPC which was supposed to be the superposition of those contributions of UHPC matrix and fibers. In this model, the shear contribution of fibers was theoretically determined using the average contribution rate of fibers in the force direction, i.e. the fiber effective factor Kf. This coefficient comprehensively revealed the effects of fiber orientation distribution, fiber efficiency and effective pull-out length. The fiber effective factors Kf in zones constrained by no, one-side and two-side moulds are 0.283, 0.408 and 0.641, respectively. The size effect caused by the wall effect of formwork was also considered in the determination of shear contribution of fibers based on Kf. The direct shear test on 14 UHPC Z-shape specimens was performed to verify the proposed model. Test results indicated that both the fiber content and the specimen size had certain influence on the direct shear strength of UHPC. The comparison with the predicted values showed that the proposed model provided relatively good predictions of the direct shear strength of UHPC.
TL;DR: In this paper , the shear behavior of dilative and non-dilative geosynthetics interfacing with sands of different morphological characteristics was analyzed through interface shear tests and a gamut of digital imaging techniques.
TL;DR: In this article , a new shear strength criterion of the rough rock-CTB interface was proposed and verified, and the results showed that the compressive deformation of the combined specimen is much larger than that of dilatancy under a higher normal stress.
TL;DR: In this paper , the authors give a background about the soil shear strength and its measurement methods based on scientific articles and the work of researchers, and discuss the soil terrain behavior as an elastic and a plastic region.
TL;DR: In this paper , the effects of basalt fiber incorporation on the mechanical properties of red clay soils were investigated through the direct shear test, unconfined compressive strength test, and microstructure test.
Abstract: The effects of basalt fiber incorporation on the mechanical properties of red clay soils were investigated. Through the direct shear test, unconfined compressive strength test, and microstructure test, the shear strength curves and stress–strain curves of basalt fiber-modified red clay soils were obtained under different basalt fiber incorporation rates and different soil dry density conditions. The results showed that: (1) the shear strength and compressive strength of the soil were significantly increased after the incorporation of basalt fiber; (2) the strength increase was greatest at 0.3% of basalt fiber incorporation, which was the optimum incorporation level; (3) the damage form of the soil changed, and the red clay soil incorporated with basalt fiber changed from brittle damage to ductile damage; and (4) the microscopic electron microscope pictures showed that, at the appropriate amount of fiber incorporation conditions, the fiber bond with the soil particles and form a fiber‒soil column. When subjected to external forces, the discrete fiber‒soil columns interact with each other to form an approximate three-dimensional fiber‒soil network, which acts to restrain the displacement and deformation of the soil particles, which is the main reason for the improved mechanical properties of the improved soil. The experimental research on the improvement of red clay soil with basalt fiber can provide a theoretical basis for engineering practice and help provide an environmentally friendly and efficient method of road base treatment in engineering.
TL;DR: In this article , the shear tests are carried out under different roughness and normal stress, and the change laws of the mechanical properties are revealed under the influence of two factors.
TL;DR: In this paper , a method for geometric quality assurance of replicas is presented for direct shear testing of a rock joint and a set of quality assurance parameters, such as σmf and VHp100, are derived and their usefulness for evaluation of geometric deviations is shown.
Abstract: Each rock joint is unique by nature which means that utilization of replicas in direct shear tests is required in experimental parameter studies. However, a method to acquire knowledge about the ability of the replicas to imitate the shear mechanical behavior of the rock joint and their dispersion in direct shear testing is lacking. In this study, a novel method is presented for geometric quality assurance of replicas. The aim is to facilitate generation of high-quality direct shear testing data as a prerequisite for reliable subsequent analyses of the results. In Part 1 of this study, two quality assurance parameters, σmf and VHp100, are derived and their usefulness for evaluation of geometric deviations, i.e. geometric reproducibility, is shown. In Part 2, the parameters are validated by showing a correlation between the parameters and the shear mechanical behavior, which qualifies the parameters for usage in the quality assurance method. Unique results from direct shear tests presenting comparisons between replicas and the rock joint show that replicas fulfilling proposed threshold values of σmf < 0.06 mm and |VHp100| < 0.2 mm have a narrow dispersion and imitate the shear mechanical behavior of the rock joint in all aspects apart from having a slightly lower peak shear strength. The wear in these replicas, which have similar morphology as the rock joint, is in the same areas as in the rock joint. The wear is slightly larger in the rock joint and therefore the discrepancy in peak shear strength derives from differences in material properties, possibly from differences in toughness. It is shown by application of the suggested method that the quality assured replicas manufactured following the process employed in this study phenomenologically capture the shear strength characteristics, which makes them useful in parameter studies.
TL;DR: In this paper , a new gravity-type grouted sleeve connection using ultra-high performance concrete (UHPC) was proposed to investigate the shear performance of the UHPC-based connection.
Abstract: This study aims to clarify the shear mechanism and strength of a new gravity-type grouted sleeve connection using ultra-high performance concrete (UHPC). Direct shear tests were conducted to investigate the shear performance of the UHPC-based connection. The test results showed that the shear strength of the UHPC-based connection is at least 50% higher than that of the traditional connection. Also, the failure mode of the UHPC-based connection is more like that of the cast-in-place (CIP) specimen than the traditional one. Based on the analysis of the shear mechanism, the formulas were proposed to predict the shear strength of the UHPC-based connection. The shear strengths obtained from the proposed formulas are in good agreement with the experimental data. To further verify the proposed formulas and investigate the shear performance, the finite element (FE) modeling method was also developed for the UHPC-based connection. It was found that the numerical results are consistent with the experimental data and the analytical results derived from the proposed formulas, indicating the applicability of the proposed formulas and FE modeling method. Parametric studies indicated that the shear strength is more sensitive to the axial load level than concrete strengths and reinforcement ratios.
TL;DR: In this paper , the post-fire shear strength of concrete-concrete interfaces after exposed to 20, 200, 400, and 600 °C was experimentally studied using Z-shape push-off tests.
TL;DR: In this paper , an experimental procedure carried out at laboratory scale on natural rock discontinuities to measure the shear strength and the roughness of their surfaces to analyse the progressive damage of the asperities during shearing process was described.
Abstract: It is well known that the mechanical behaviour of rock discontinuities strongly influences the stability of slopes and fractured rock walls. With this end, particular attention must be paid to the analysis of the roughness of natural discontinuities, which represents a peculiar geometric feature strongly influencing their shear strength. The paper describes an experimental procedure carried out at laboratory scale on natural rock discontinuities to measure the shear strength and the roughness of their surfaces to analyse the progressive damage of the asperities during shearing process. The direct shear tests along discontinuities were coupled to photogrammetric surveys of the surfaces carried out before the tests (natural surfaces), after the first cycle and at the end of the last cycle. This allowed the reconstruction of the digital surface models of the intact and degraded surfaces. Through analytical procedures, the data obtained were processed to obtain geometric descriptors and adequately estimate the Joint Roughness Coefficient (JRC), analysing several profiles extracted along the direction in which the mechanical tests were conducted. The comparison between the experimental results and the roughness surface direct measure showed that discontinuities, even at the small scale, have an inhomogeneous roughness and that discontinuity degree of damage is a progressive process influenced by the state of confinement applied during the tests.
TL;DR: In this paper , a series of undrained strength tests with a Berkeley simple shear apparatus were performed on three reconstituted natural clays and one artificial clay with a range of coefficients of consolidation.
Abstract: The undrained shear strength of clay is an important parameter for the design of embankments, shallow foundations, and pile foundations. Among the various methods of testing undrained strength, the simple shear is essential when the shearing mode of the soil surrounding the pile is similar to that in a simple shear test. This study employs a series of undrained strength tests with a Berkeley simple shear apparatus. Three reconstituted natural clays and one artificial clay were tested with a range of coefficients of consolidation. The influence factors, including sample pre-consolidation pressure, saturation back pressure, shearing rate, height of specimen, consolidation stress, and lateral stress ratio, were investigated in undrained simple shear tests. The failure mode in simple shear and corresponding strength parameters are also examined. Based on the test data set, models for describing the undrained strength with simple shear for high plasticity clays are developed and compared to test data for normally consolidated reconstituted clay. Good agreement between models and intact Onsoy clay is also observed when allowance is made for the coefficient of consolidation and strength parameters of undisturbed clay and in situ stress state.
TL;DR: In this paper , the effect of moisture on the shear bond performance and failure process of the PU-concrete interface before and after grouting PU with different densities was investigated.
Abstract: The bond resistance between polyurethane (PU) grouting material and concrete consists of adhesion, friction, and mechanical interlocking and is crucial to the repaired concrete structures. During the repair of the leakage and subsidence of underground concrete pipelines by PU grouting material, the chemical adhesion between PU and concrete interfaces may be influenced by moisture caused by the pipeline leakage and groundwater. In this paper, shear tests and the digital imaging correlation (DIC) method were used to study the effect of moisture on the shear bond performance and failure process of the PU-concrete interface before and after grouting PU with different densities. The results reveal that the differences in bond strength, shear strain and horizontal displacement between the interfaces are significantly reduced with the polymer density, especially for moistened interfaces before grouting and testing. Finally, a finite element model was employed to simulate the bond strength between PU and concrete and validated based on the test results.
TL;DR: In this paper , a series of twelve shear tests on members with plain and ribbed bent-up bars is presented, and the contribution of the bentup bars to the shear strength is evaluated by combining the constitutive laws of various shear transfer mechanisms along an idealised shear crack.