Showing papers on "Direct shear test published in 2015"
TL;DR: In this paper, the effect of bedding plane orientations on shear strength and failure mechanisms of shale is investigated, with an emphasis on the shear parameters of the bedding planes.
157 citations
TL;DR: In this article, the effect of size of the particles on the shear and interfacial shear strength of sands is presented through direct and interface direct shear tests complemented with image analyses and surface roughness studies.
Abstract: Size and morphological characteristics of particles play vital role on the shear and interfacial shear strength of sands. Often, effects of these parameters are merged and cannot be easily separated. Effect of size of the particles on the shear and interfacial shear strength of sands is presented in this paper through direct shear and interface direct shear tests complemented with image analyses and surface roughness studies. To eliminate the effect of morphological characteristics, three sands of different particle sizes with similar morphological characteristics like angularity, roundness, sphericity and roughness were selected for the study. These morphological characteristics for all three sands were determined from the analysis of scanning electron microscope images and were found to be similar for all three sands. It was observed from the symmetric direct shear tests that the particle size has no effect on the peak friction angle when the tests were carried out at same void ratio. However, ultimate friction angles were affected by the particle size. Shear band thickness was estimated from image segmentation analysis of the profiles of colored sand columns during shear and the same was correlated to the particle size. Interface direct shear tests were carried out on sand–geomembrane interfaces to study the effect of particle size on the interfacial shear strength. Microscopic images of geomembranes were captured after the interface shear tests to understand the change in surface roughness of the geomembrane due to particle indentations. Surface roughness studies on geomembrane samples after the tests confirmed that the plowing and groove formation on geomembranes during interface shear tests depend on the particle size as well as the relative roughness of the sand particles with respect to the membrane. Sand of medium particle size showed highest interfacial strength because of more number of effective contacts per unit area of the interface.
117 citations
TL;DR: In this article, the authors set out an approach to assess shear strength of rock joints at project scale based on measurement and analysis rather than empiricism, and illustrated a case example of a spillway slope for a dam in the Himalayas.
Abstract: This paper sets out an approach to assessing shear strength of rock joints at project scale based on measurement and analysis rather than empiricism. The role of direct shear testing in this process is discussed in detail and the need for dilation measurement and correction emphasised. Dilation-corrected basic friction angles are presented for various rock types. The characterisation of first and second order roughness features and their contribution to shear strength at project scale are discussed with reference to possible scale effects. The paper is illustrated by a case example of a spillway slope for a dam in the Himalayas.
113 citations
TL;DR: In this paper, the authors focused on the bond strength of cemented concrete-rock joints and showed that the shear strength of joints with good adhesion is strongly dependent on the strength of the cohesive interfaces when applied normal stress is less than 6 MPa.
Abstract: The shear behaviour of cemented concrete–rock joints is a key factor affecting the shear resistance of dam foundations, arch bridge foundations, rock socketed piles and rock bolts in rock engineering. This paper presents an experimental and numerical investigation of the shear behaviour of cemented concrete–rock joints by direct shear tests. In this study we focused on the bond strength of cemented concrete–rock joints, so limestone with smooth surfaces was used for samples preparation to reduce the roughness effect. The experimental results show that the shear strength of joints with good adhesion is strongly dependent on the bond strength of the cohesive interfaces when the applied normal stress is less than 6 MPa. In addition, the sudden and gradual bond failure processes of the cohesive interfaces were observed with an increase of the normal stress. A simple, yet realistic, model of cemented concrete–rock joint is proposed to simulate the observed behaviour, including elastic behaviour of the bond before peak shear stress and post-peak behaviour due to bond failure and friction increase. Finally, the parameters analysis and calibration of the proposed model are presented.
108 citations
TL;DR: In this paper, the particle flow code PFC2D was used to simulate the shear behavior of smooth joints in a direct shear test using the modified smooth joint (SJ) model.
Abstract: This paper aims to study the shear behaviour of rock joints in a direct shear test using the particle flow code PFC2D. In this numerical approach, the intact rock is simulated by densely packed circular particles that are bonded together at their contact points; joint surfaces can be explicitly simulated using the modified smooth joint (SJ) model. In the modified SJ model for simulation of direct shear test, micro-scale slip surfaces (smooth joint contacts)
are applied at contacts between the particles of the upper and lower blocks of the shear box and the mechanical behaviour of the joints is controlled by the micro-scale properties of the smooth joint contacts. Two joint profiles of standard JRC 10–12 and a sawtooth triangular joint with a base angle of 15° were selected for testing. The results of direct shear tests under different normal stresses on these two profiles show that for the sawtooth triangular joints under a normal stress of 1 MPa, the shearing mechanism is purely sliding, and for the JRC 10–12 profile under a normal stress of 4 MPa, the shearing of first-order asperities controls the shearing mechanism. A parametric study of the micro-properties of the smooth joints under these two different shearing mechanisms was undertaken. The results of this study show that the SJ normal stiffness and the SJ shear stiffness have insubstantial effect on the peak shear strength in sliding mode, but that the SJ normal stiffness has a significant effect on the dilation rate in both sliding and shearing modes.
107 citations
TL;DR: In this paper, the authors investigated the effect of adding nano-SiO2 and recycled polyester fiber on soil engineering properties, especially the shear strength and unconfined compressive strength (UCS), using clayey soil with low liquid limit.
Abstract: This paper investigates the effect of recycled polyester fiber, produced from polyethylene (PET) bottles, in combination with nano-SiO2 as a new stabilizer to improve the mechanical properties of soils We intend to study the effect of adding nano-SiO2 and recycled polyester fiber on soil engineering properties, especially the shear strength and unconfined compressive strength (UCS), using clayey soil with low liquid limit Three different combinations of fiber-soil ratios ranging between 01% and 05% as well as three different combinations of nano-soil ratios ranging between 05% and 1% are used The shear strength and UCS of treated specimens are obtained from direct shear test and unconfined compression test, respectively Results of this study show that the addition of recycled polyester fiber and nano-SiO2 increases the strength of soil specimens Both the shear strength and UCS are improved by increasing the contents of recycled polyester fiber and nano-SiO2 in the soil mixture The increase in the nano-SiO2 content leads to a reduction in failure strain, but the increase in the content of recycled polyester fiber leads to an increase in failure strain The increase in the contents of recycled polyester fiber and nano-SiO2 leads to an increase in elastic modulus of soils Based on the test results, the addition of recycled polyester fiber improves the mechanical properties of soils stabilized with nano-SiO2 as well as the recycled polyester fiber has a positive effect on soil behaviors
106 citations
TL;DR: In this paper, the impact of F-T cycles on the mechanical properties of two types of plastic soils, stabilized with lime, were investigated and the results indicated that the volume of the treated soils increased during the first F−T cycles, after which this increase became less pronounced.
103 citations
TL;DR: In this paper, the authors evaluated regular surface roughness and its effect on interfacial shear behavior of the red clay -concrete interface and presented the results of a series of experiments.
Abstract: Few studies have focused on evaluating regular surface roughness and its effect on interfacial shear behavior of the red clay – concrete interface. This paper presents the results of a series of la...
101 citations
TL;DR: In this article, a new analytical model was proposed to describe the complete shear behavior of rough joints under constant normal stiffness (CNS) boundary conditions by incorporating the effect of damage to asperities.
Abstract: The shear behaviour of a rough rock joint depends largely on the surface properties of the joint, as well as the boundary conditions applied across the joint interface. This paper proposes a new analytical model to describe the complete shear behaviour of rough joints under constant normal stiffness (CNS) boundary conditions by incorporating the effect of damage to asperities. In particular, the effects of initial normal stress levels and joint surface roughness on the shear behaviour of joints under CNS conditions were studied, and the analytical model was validated through experimental results. Finally, the practical application of the model to a jointed rock slope stability analysis is presented.
98 citations
TL;DR: In this paper, double-lap and single-lap shear tests were used to investigate the bond behavior and stress transfer mechanism of polyparaphenylene benzobisoxazazole (PBO) fiber-reinforced cementitious matrix composites bonded to a concrete substrate.
Abstract: This paper presents the results of an investigation on the bond behavior and stress-transfer mechanism of polyparaphenylene benzobisoxazole (PBO) fiber-reinforced cementitious matrix (FRCM) composites bonded to a concrete substrate using double-lap and single-lap shear tests Results of double-lap shear tests with different composite bonded lengths and widths are presented and compared with those from single-lap shear tests previously reported by the authors The idealized load response developed from single-lap shear tests is found to characterize the response of the composite in double-lap shear tests, although with a few key differences With the double-lap shear test, load redistribution among the composite strips influences the post-peak response if debonding does not occur equally in both strips Values of the ultimate (peak) stress determined using double-lap shear tests are generally consistent with, although slightly lower than, those determined by single-lap shear tests when the bonded length is longer than the effective bond length
96 citations
TL;DR: In this paper, an extensive laboratory study carried out using a large-scale direct shear test device, in which the influence of soil moisture content, soil density and geosynthetic type was evaluated.
Abstract: Soil–geosynthetic interface shear strength is an essential parameter for the design and stability analysis of geosynthetic-reinforced soil structures. Economic and environmental reasons have led to increasing use of locally available residual soils with a significant percentage of fines and lower draining capacity, when compared with the traditional good-quality backfill materials. This paper describes an extensive laboratory study carried out using a large-scale direct shear test device, in which the influence of soil moisture content, soil density and geosynthetic type on the direct shear behaviour of the soil–geosynthetic interface was evaluated. The study involved a locally available granite residual soil and four geosynthetics: two geogrids (one uniaxial and the other biaxial), one geocomposite reinforcement (high-strength geotextile) and one geotextile. Test results have revealed that the increase in soil moisture content can measurably reduce the soil–geosynthetic interface shear strength...
TL;DR: In this article, an experimental study on SMA bars subject to cyclic direct-shear actions, and uniaxial tensile tests were also undertaken on the bars of similar sizes for comparison.
Abstract: Shape memory alloys (SMAs) are smart metals featuring either superelastic effect or shape memory effect. While current emphasis on the civil engineering application of SMA is mainly given to dampers and isolators, recent research has been directed to superelastic SMA bolts or tendons for recentring connections. However, available information on the mechanical shear response of SMA bars is still inadequate. Consequently, this knowledge barrier can cause significant uncertainties when such components are intended to resist shear action. In this respect, this paper presents an experimental study on SMA bars subject to cyclic direct-shear actions, and uniaxial tensile tests were also undertaken on the bars of similar sizes for comparison. Key results including stress–strain/force–displacement hysteretic response, recentring ability, and energy dissipation are discussed in detail. The results show sound recentring and moderate energy dissipation/damping capabilities of the bars under cyclic tension below a strain level of 3 %, but beyond this the properties start to degrade. The SMA bars with a smaller diameter seem to perform better than those with a larger diameter. On the other hand, the cyclic direct-shear performance of SMA bars is generally unsatisfactory with poor recentring, energy dissipation, and damping characteristics. Therefore, the direct use of SMA bars subject to shear loading is undesirable. For both tension and shear tests, fracture of the bars within the threaded area is the most typical failure mode, which should be minimised in future applications to ensure a ductile response of seismic resistance devices. Recognising both advantages and potential shortcomings of the SMA bars, an innovative recentring connection type is proposed, and the preliminarily findings indicate that such connections are feasible.
TL;DR: The microstructure and alloy element distribution across the TA1/X65 interfaces of as-welded, heat treated and extruded TA 1/X 65 bimetallic sheets were studied and compared as discussed by the authors.
TL;DR: A discrete element model with a general contact force law for arbitrarily shaped particles was developed in this article, in which angular particles were modeled using convex polyhedra and four categories of assemblies with different angularities were generated.
Abstract: This paper investigated the effect of the particle angularity in light of its importance in angular particle assemblies, using the discrete element method (DEM). A discrete element model with a general contact force law for arbitrarily shaped particles was developed, in which angular particles were modeled using convex polyhedra. Quasi-spherical polyhedral shapes with different vertexes were adopted to reflect the change of angularity. Four categories of assemblies with different angularities were generated. A series of direct shear tests performed on these assemblies were simulated at different vertical stresses. All numerical implementations were achieved using a modified version of the open source DEM code YADE. It was found that the macroscopic shear strength and dilatancy characteristics are in agreement with experimental and numerical results in the literature, indicating that the present numerical model is reasonable. Besides, the evolutions of coordination number, normal contact force distribution, and anisotropies of particle orientation and contact normal were investigated. The results show that the angularity plays a vital role in strengthening the interlocking of angular particles.
TL;DR: In this paper, the effect and mechanism of rock strength on the mechanical behavior and fracture mode of the composite samples of coal-coal-rock composite samples are analyzed, and the results show that major failure modes of composite samples were conjugate X-shaped shearing fracture and splitting fracture.
Abstract: Many dynamic events in coal mine are caused by the instability of coal–rock body. In order to study the influence of rock strength on this type of instability, uniaxial compression experiments of rock–coal–rock composite samples with different rock strengths are carried out, and the effect and mechanism of rock strength on the mechanical behavior and fracture mode of the composite samples are analyzed. The results show that major failure modes of the composite samples are conjugate X-shaped shearing fracture and splitting fracture. The angle between the shear fracture surface and the end face increases with rock strength. The splitting fracture in the coal body expands to the rock when the rock strength is low. The strength properties of the composite samples mainly depend on the coal strength instead of the rock strength. With the rock strength increasing, the peak strain of the composite samples decrease, and the differences from the coal strain and strain rate to rock strain and strain rate become greater. These failure modes and characteristics of deformation are shown to be determined by the difference between the elastic modulus of rock and coal constituting the composite samples.
TL;DR: In this paper, a novel bond contact model is proposed for jointed rock slope failure and validated by a series of numerical direct shear tests on jointed models and the comparisons to laboratory test results.
TL;DR: In this article, the engineering properties of foamed recycled glass were assessed through a laboratory evaluation to ascertain this novel recycled material as a lightweight fill material in civil engineering applications. And the energy savings assessment demonstrates that the use of the recycled glass as engineering material has much lower energy consumption relative to a conventional aggregate-cement material in construction projects.
TL;DR: In this paper, the authors quantified the effect of soil water content on the reinforcement of soil by plant roots and determined how soil water contents influenced the failure modes of roots during shear.
Abstract: The use of vegetation to stabilize slopes with regard to shallow landslides is an ecological and economic alternative to traditional solutions of civil engineering. This study aims at quantifying the effect of soil water content on the reinforcement of soil by plant roots and determines how soil water content influences the failure modes of roots during shear. Direct shear box tests were performed on three species used in hillslope reforestation programs in Yunnan, China. Reinforcement was quantified and divided into a hydric component corresponding to the effect of water removal and a mechanical component reflecting the influence of roots on apparent cohesion and friction angle. It was shown that the hydric component of reinforcement can be of the same order as the mechanical component and that root system architectural traits influence the type of mechanical reinforcement (cohesive or frictional). We also demonstrate the potential development of matric suction effects on the shear strength of soil.
TL;DR: In this article, the influence of the lay-up configuration on interlaminar and in-plane shear properties of glass fiber reinforced epoxy composites was studied. And the dynamic shear modulus was measured with non-destructive testing based on free vibration method.
TL;DR: In this article, a numerical analysis model was established based on finite-element code to investigate structural behavior of precast concrete segmental bridges under direct shear, and the concrete damage plasticity model along with the pseudodamping scheme were incorporated to analyze the system for micro-cracks and to stabilize the solution, respectively.
Abstract: © 2014 This work is made available under the terms of the Creative Commons Attribution 4.0 International license,. The structural behavior of precast concrete segmental bridges largely depends on the behavior of the joints between segments. The current practice of precast concrete segmental bridges is to use small keys that are usually unreinforced, normally dry, and distributed over the height of the web and the flange of concrete segments. In this study, a numerical analysis model was established based on finite-element code to investigate structural behavior of keyed dry joints under direct shear. The concrete damage plasticity model along with the pseudodamping scheme were incorporated to analyze the system for microcracks and to stabilize the solution, respectively. The numerical model was calibrated by full-scale experimental results described in the literature. It was found that the predicted ultimate load, cracking evolution history, and final crack pattern agreed reasonably well with experimental results. The validated numerical model was then used for parametric study on factors affecting shear behavior of keyed dry joints, in this case confining pressure. The authors found that shear capacity predicted by the AASHTO code equation diverges from that predicted by numerical analysis at high confining pressure, because the contribution of friction in the total shear capacity decreased with an increase in confining pressure. Hence, the authors recommend reducing the friction coefficient used in the AASHTO code equation when high confining pressure is applied. Moreover, the propagation of inclined crack was arrested at high confining pressure owing to the fact that the fracture propagation direction is governed by the criterion of the maximum energy release rate.
TL;DR: In this paper, the average cohesion and friction angle of the coal-rock interfaces are 0786 MPa and 297 degrees, respectively, while the normal stiffness of coalrock interface ranges from 057 to 444 MPa/mm.
TL;DR: In this article, the performance of two types of rock bolts, fully encapsulated rebar and D-Bolt, under combined pull and shear loading were studied in the laboratory.
TL;DR: In this paper, the authors focused on the titanium alloy Ti-6Al-4V diffusion bonded to AISI 304 stainless steel with silver foil as an interlayer, and the results from mechanical testing showed that shear strength values have a direct relationship with bonding time.
TL;DR: In this article, the effect of a vegetation root matrix on a soil slope and focusing on mechanical reinforcement using an example of vetiver grass (Vetiveria nemoralis A. Camus) specimens, grown for under a year, were used in this study.
TL;DR: In this paper, a radial groove is cut out to keep the fracture away from the clamping area, which can be used as a shear fracture test for sheet materials and is able to create material fracture under ideal shear conditions i.e., the condition of vanishing triaxiality at the observable region of the test.
TL;DR: In this paper, a series of large-scale direct shear tests were carried out to investigate the interface shear strength of subballast stabilised with geogrids and geomembranes, respectively.
TL;DR: In this paper, a series of constant normal load direct shear tests was performed to investigate the shear strength of artificial samples with infilled rough joint surfaces having different asperity and infill characteristics.
Abstract: Infill materials in rock joints usually cause a reduction in the joint shear strength. The shear behavior of rock discontinuities depends upon whether they are clean and unfilled or filled, so this concern invites accurate understanding of the shear behavior and strength of infilled joints. A series of constant normal load direct shear tests was performed to investigate the shear strength of artificial samples with infilled rough joint surfaces having different asperity and infill characteristics. The current study focuses on the effects of factors that influence the shear strength of infilled rock joints samples, with emphasis on forward and reverse shearing. In the forward cycle, the front joint wall is compressed and possibly sheared, and the back side fill is unbonded from the joint surface and slightly disturbed. In the reverse cycle, the disturbed and weakened back side fill is under shearing. The effect of the normal stress on the joint is studied, as this factor plays an important role on the shear behavior of infilled rock joint samples. The results show that joints with low asperity angle exhibit higher shear strength during the forward shearing cycle than the reverse cycle, but in joints with steeper asperity angle, the reverse cycle exhibits greater shear strength. In the reverse cycle, the joint infill has less influence compared to the effect of the rougher surface and higher asperity inclination, even in higher normal stress.
TL;DR: In this paper, a constitutive model for rock joints was developed that considers the dilation and strength along both small-scale joint roughness scaled from laboratory data, and large-scale waviness determined from geologic observations.
TL;DR: An experimental program was performed to study the effects of cement stabilization on the geotechnical characteristics of sandy soils as discussed by the authors, where lime Portland cement was added in percentages of 2.5, 5 and 7.5% by dry weight of the soils.
Abstract: An experimental program was performed to study the effects of cement stabilization on the geotechnical characteristics of sandy soils. Stabilizing agent included lime Portland cement, and was added in percentages of 2.5, 5 and 7.5% by dry weight of the soils. An analysis of the mechanical behavior of the soil is performed from the interpretation of results from unconfined compression tests and direct shear tests. Cylindrical and cube samples were prepared at optimum moisture content and maximum dry unit weight for unconfined compression and direct shear tests, respectively. Samples were cured for 7, 14 and 28 days after which they were tested. Based on the experimental investigations, the utilization of cemented specimens increased strength parameters, reduced displacement at failure, and changed soil behavior to a noticeable brittle behavior.