Explore the vast range of titles available.

It is of great significance to investigate the shear mechanical behavior of pile–structural soil interface (PSSI) for guiding the design and construction of pile foundations in structural soft soil areas. The available studies rarely consider the effect of shear rate on the shear behavior of the PSSI under large deformation, and a relevant constitutive model is still lacking. In this paper, the effect of shear rate on the shear behavior of the PSSI under large deformation is investigated using a series of ring shear tests with different shear rates. Based on the test results, damage theory is introduced to analyze the mechanism of shear damage of the PSSI, and an interface damage constitutive model is proposed to describe the shear mechanical behavior of the PSSI under large deformation. Finally, a method for calculating the brittleness index of the PSSI is proposed based on the interface constitutive model. The evolution of the shear stress of the PSSI is analyzed, and the shear mechanical behavior of the PSSI under any normal stress is evaluated. The results show that the PSSI subjected to large deformation exhibits strain softening and has stable residual strength. The shear strength of the interface first decreases and then increases with increasing shear rate. The interface constitutive model can accurately reflect the shear behavior of the PSSI under large deformation. The shear rate has a positive effect on the brittleness index of the PSSI, and the normal stress amplifies this effect. The interface constitutive model can also predict the effect of normal stress on the brittleness index.

A series of monotonic and multidirectional cyclic simple shear tests were performed on reconstituted fiber-reinforced calcareous sand specimens prepared by the dry deposition method, at a relative density of approximately 50%, considering the effects of fiber contents and cyclic stress levels. The peak shear strength, the linkage between monotonic and cyclic behaviors, liquefaction resistance, and pore pressure responses of calcareous sand with and without fiber reinforcement were analyzed. The results indicate that both unreinforced and fiber-reinforced calcareous sand exhibit limited flow instability behavior and the peak shear strength increases with the increase in fiber content under monotonic loading. The inclusion of fibers and increasing fiber contents can improve the liquefaction resistance of calcareous sand under cyclic loading. A linear relationship was found between the normalized liquefaction resistance of reinforced sand and the number of cycles for triggering liquefaction, and the prediction of liquefaction resistance of fiber-reinforced calcareous sand with various fiber contents can be conveniently achieved according to the linear relationship. The pore pressure prediction model considering the effect of fiber contents was proposed, which was capable of effectively simulating the pore pressure generation of fiber-reinforced calcareous sand.

Joint properties play a controlling role in the strength of rock mass. In response to the situation that existing researches on bolting mechanism of bolted rock joints principally concentrate on the macroelements, such as rock properties, bolting angle and joint morphology, the direct shear tests on unbolted and single-bolted rock joints under the conditions of different normal stress and different joint microproperties by numerical calculation method of particle flow (PFC) were carried out in this paper to reveal the microbolting mechanism and study the influences of joint properties. Subsequently, a comprehensive comparison of microfailure characteristics between unbolted and single-bolted rock joint demonstrated that during the shearing process, a triangle extrusion reinforcement area emerges around the bolt, where microcracks are extremely developed and rock blocks are considerably fractured, but it also improves the anti-shearing efficacy of rock joint. Meanwhile, both the macroshear behavior and microfailure characteristics of single-bolted rock joints with different joint microproperties was analyzed by comparing the shear stress–shear displacement curves and crack development. Specifically, the shear stiffness of single-bolted rock joints enhances with the increase of joint tangential stiffness, and the augmentation of joint tangential stiffness or friction coefficient intensifies the shearing resistance of single-bolted rock joints, whereas the joint normal stiffness was proven to share a negative correlation with the shear strength of single-bolted rock joints. Besides, the shear stiffness of single-bolted rock joints decreases approximately linearly with the increasing joint thickness. In addition, the thicker the joint, the lower the peak shear stress of single-bolted rock joints. With the increase of joint thickness, the crack number of single-bolted rock joint failure decreases, and the particle confinement of bolt is enhanced.

The non-persistent jointed rock mass is prone to compressive-shear and tensile-shear failures. Tensile-shear failure has been studied less than compressive-shear failure. This study develops a new shear test apparatus for cubic rock specimens to explore the tensile-shear failure of jointed rock mass under varying joint persistence and compare it to compressive-shear failure. The jointed rock specimens are sheared and monitored using acoustic emission (AE) equipment, an infrared thermal imager, and a high-speed camera to track stress, AE signal, temperature, and deformation. Based on the test results, RFPA2D numerical simulation is conducted to investigate the effect of joint persistence on the compressive- and tensile-shear strength of the rock bridge. Tensile- and compressive-shear stress curves differ greatly. The former may have several stress peaks and peak AE count time does not equal peak strength time. The rock specimen’s compressive-shear strength is far higher than its tensile-shear strength, but tensile-shear tests accumulate more AE counts and energy. Tensile-shear failure has a large crack opening and rapid temperature progression. The rock specimen cools before peak strength, which is the opposite of compressive-shear failure. The two tests differ significantly regarding crack development and deformation evolution. The shear strength of the specimens in the compressive-shear and tensile-shear tests decreases approximately linearly as joint persistence increases, and the shear strength of the rock bridges increases and then decreases. Previous research showed that increasing joint persistence increases rock bridge cohesiveness. At relatively high joint persistence, however, the considerable cohesion weakening of the rock bridge caused by tensile cracks near the joint tip should be considered. The findings could contribute to a better understanding of the failure process of jointed rock mass under compressive-shear and tensile-shear stresses.HighlightsCompressive- and tensile-shear tests on cubic rock-like specimens were conducted on a novel test apparatus.Effect of joint persistence on compressive- and tensile-shear failure behavior was investigated.AE, thermal infrared imager, and DIC technologies were utilized to analyze the failure mechanism difference between compressive- and tensile-shear tests.The rock bridge's shear strength increases first and then decreases with joint persistence increasing in both compressive- and tensile-shear tests.

Soil constitutive models are widely investigated and applied in soil mechanical behaviors simulation; however, the damage evolution process of soil with various shear deformation behaviors was rarely studied. This study introduces a novel shear constitutive model for slip zone soil considering its damage evolution process. Firstly, an innovative method for determining the shear stiffness is proposed to assess the damage degree of slip zone soil during shear deformation. Further, a damage evolution model based on the log-logistic function is derived to characterize the damage evolution process of slip zone soil, and a new shear constitutive model based on the damage evolution process is subsequently proposed. Both the damage evolution model and the shear constitutive model are verified by the ring shear test data of the slip zone soil from the Outang landslide in the Three Gorges Reservoir area of China. Compared to the traditional peak-solving constitutive model based on the Weibull distribution, the proposed shear constitutive model has the distinct advantage of describing not only the brittle (strain softening) mechanical behavior but also the ductile and plastic hardening mechanical behavior of soil. In summary, this method offers a rapid determination of the damage evolution process and the shear behavior constitutive relationship of slip zone soil in landslides.

This paper presents an experimental study on rolling shear (RS) strength properties of non-edge-glued cross-laminated timber (CLT) made out of New Zealand Radiata pine ( Pinus radiata ) structural timber. CLT specimens with 35 and 20 mm thick laminations were studied to evaluate the influence of lamination thickness on the RS strength of CLT. Short-span three-point bending tests were used to introduce high RS stresses in cross layers of CLT specimens and facilitate the RS failure mechanism. Modified planar shear tests from the conventional two-plate planar shear tests were also used to evaluate the RS strength properties. It was found that two test methods yielded comparable RS strength properties and the lamination thickness significantly affected RS strength of the CLT specimens. The test results also indicated that the recommended characteristic RS strength values of CLT products in Europe and Canada might be over conservative. Also, it might be more efficient to specify different RS strength values for CLT with different lamination thickness given the minimum width-to-depth ratio of laminations is satisfied.

The shear modulus and shear strength of extruded polystyrene foam were obtained by the in-plane shear and asymmetric four-point bending tests. In addition, the test data were numerically analysed, and the effectiveness of these tests was examined. The numerical and experimental results suggest that the shear modulus and shear strength obtained from the in-plane shear test are significantly smaller than those obtained from the asymmetric four-point bending test because the influence of the stress concentration was less significant. Although the in-plane shear test is standardised in ASTM C273/C273M-11, it is considerable to adopt the asymmetric four-point bending test as another candidate for obtaining the shear properties of extruded polystyrene foam.

Interparticle friction is an intrinsic property of particles, which plays an important role in the macroscopic and microscopic shear mechanical properties of granular materials. In this research, we investigate the shear behavior of granular materials with different friction coefficients using ring shear tests. The particle image velocimetry (PIV) technique was also used to analyze the shear flow characteristics. The results indicate that the peak shear strength of granular materials increases with the increase in shear rates, especially for granular materials with high friction coefficients. The shear stress fluctuation difference is smaller under low normal stress. Under high normal stress, the shear stress fluctuation of granular materials with high friction coefficient is higher than that of granular materials with low friction coefficient. In addition, the shear stress fluctuation shows a trend of increasing with the increase of shear rates. The range of the liquid phase flow region of granular materials decreases with the increase of friction coefficient and normal stress. This work reveals the shear flow characteristics of granular materials under different conditions, which can provide reference for the flow processes of geological disasters such as landslides and debris flows.

The three-dimensional (3D) morphology of a rock joint has a great impact on its shear behavior. To study the relationship between the 3D morphological characteristics and the peak shear strength, several tilt tests were conducted on four groups of tensile fractures and direct shear tests were carried out under different constant normal loads (CNL). The normal load ranges from 0.325 to 8.0 MPa. In this study, fresh tensile fractures which were splitted from granite and sandstone samples were used. The morphology of each tensile fracture was measured before direct shear tests. A new peak shear strength criterion for rock joints is proposed using two 3D morphological parameters which are termed as the maximum apparent dip angle θ max ∗ and the roughness parameter C . The calculated peak strengths using the proposed criterion match well with the observed values. In addition, a comparison of the proposed model with the Grasselli’s model ( 2003 ) and Xia’s model ( 2014 ) shows that the proposed model is easier in the form and gives a rational improvement. At last, direct shear test data of tensile fractures which are collected from Grasselli ( 2003 ) are used to verify the proposed model. It is seen that the proposed model has a reliable estimate of the peak shear strength of tensile fractures and presumably for rock joints.

Soil-rock mixture is a commonly used geotechnical material used in many construction projects, such as slopes, tunnels, and dams. The shear strength of soil-rock mixture is its key property and is affected by many factors. This study aimed to investigate the shear strength characteristics of soil-rock mixture and the influences of moisture and stone content on shear strength parameters. Soil-rock mixture samples with four different stone and moisture contents were fabricated and tested using a large-scale direct shear test apparatus under four vertical pressures. The results demonstrated that the shear properties of the soil-rock mixture showed significant Mohr Coulomb failure criteria for all stone contents. As the moisture content increased, the shear strength of the soil-rock mixture first increased by 10~18% and then decreased after w = 12% to the residue value. The change in cohesion and internal friction angle of soil-rock mixture with different moisture contents shared a similar trend. For w < 12%, the cohesion and internal friction angle increased with moisture content, and for w > 12%, the two indexes obviously decreased. As the stone content increased from 30% to 60%, the shear strength of the soil-rock mixture increased by 82~174%. The internal friction angle increased linearly with stone content, while the cohesion of the mixture first increased and then decreased after the stone content reached 50%. The results can help in the designation and application of soil-rock mixture.