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

High-strength bolt connectors, known for their robust strength and ease of disassembly, are suitable not only for the construction of new steel–concrete composite beams but also for reinforcing existing composite or steel beams. Static push-out tests were performed on nine specimens to examine their shear behavior. The primary failure mode was observed at the steel–concrete interface, characterized by the tensile–shear failure of the bolt and localized crushing of the concrete beneath the bolt. The preload had no significant influence on the ultimate bearing capacity and ultimate slip displacement, while it had a substantial impact on the initial slip load. The failure process was divided into static friction at the interface, sliding at the interface, elastic deformation of the bolt, and plastic deformation of the bolt. The parametric analysis using the finite element method was performed to assess the impact of concrete strength, reserved hole diameter, interface friction coefficient, and bolt diameter and strength. It revealed that the ultimate bearing capacity is composed of interfacial friction and bolt shear capacity, which are not independent of each other. To decouple these components, a novel calculation method for determining the ultimate bearing capacity of high-strength bolt connectors was developed and validated using existing test data.

This study aimed to examine the impact of various production parameters on the shear performance at the interface between geopolymer mortar (GPM) and sand soil. Initially, the effects of varying NaOH concentrations (5, 10 and 15 M), aggregate types (stream aggregates (SA), crushed stone aggregates (CS) and construction and demolition waste (CDW) aggregates) and alkali/binder ratios (0.5 and 0.6) on GBFS-based GPM specimens were investigated. For this purpose, compressive strength, water absorption and ultrasonic pulse velocity (UPV) tests were carried out on GPM samples cured for 28 days. The maximum 28-day compressive strength (43.6 MPa) and the minimum water absorption (3.78%) were observed in GPM specimens activated with 15 M NaOH, produced with CS, water-cured and cast at an alkali/binder ratio of 0.5. Experimental findings revealed that the effects of aggregate type on high mechanical and low permeability properties were graded as CS > SA > CDW. Additionally, UPV test results showed positive correlation with compressive strength and water absorption values. Subsequently, the shear performance between GPM and sand soil were determined by using shear box test. In direct shear experiments, decreasing the alkali/binder ratio from 0.6 to 0.5 and the usage of CS increased the sand–GPM friction angle. Moreover, numerical modelling was employed to analysed soil-GPM interaction using the finite element method (FEM) in ABAQUS. FEM results showed that the obtained numerical findings demonstrated strong consistency with experimental data, capturing force–displacement trends therefore the numerical model can be used for parametric studies.

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.

Calcareous sands have abundant intraparticle pores and are prone to particle breakage. This often leads to poor engineering properties, which poses a challenge to coastal infrastructure construction. A study using bio-cementation to improve the engineering properties of calcareous sand is presented in this paper. The macro- and microscopic properties of bio-cemented calcareous sand were characterized by drained triaxial tests and scanning electron microscopy observations. Experimental results show that the precipitated calcium carbonate can effectively fill the intra- and interparticle pores and bond adjacent particles, thus enhancing the shear strength of calcareous sand. The special structures (e.g. abundant intraparticle pores and rough surface) and mineral components (i.e. calcium carbonate) of calcareous sand are beneficial for improving bacterial retention in soil, which leads to a relatively uniform and dense calcium carbonate distribution on the sand particle surface, exhibiting a layer-by-layer growth pattern. This growth pattern and the abundant interparticle pores would result in less effective calcium carbonate. The strength enhancement of bio-cemented calcareous sand is significantly lower than that of bio-cemented silica sand at the same calcium carbonate content, which may be caused by the differences in the following: (a) soil skeleton strength; (b) the amount of effective calcium carbonate; and (c) interparticle pore-filling of calcium carbonate.

The shear modulus behaviour of weathered red sandstone coarse-grained soil under drying–wetting cycles was investigated using a series of triaxial drained tests. Firstly, the properties of the relationship between shear stress q and shear strain εs were analysed using the test curves of principal stress difference (σ1-σ3) and shear strain εs based on a series of triaxial drained tests performed; Secondly, a method for solving tangent shear modulus Gt was established according to the test curves of σ1-σ3 – εs, and the effect of drying–wetting cycles on initial tangent shear modulus Gi was analyzed; Finally, the normalisation equation of (σ1-σ3) – εs was proposed. The results are as follows: (1) Under the influence of drying–wetting cycles, the (σ1-σ3)-εs test curve of weathered red sandstone coarse-grained soil are approximately hyperbolas, and the stress–strain relationship between εs and (σ1-σ3) exhibits strain hardening. (2) The initial tangent shear modulus Gi decreases with the increase of the number of drying–wetting cycles, and the decreased amplitude is large at high confining pressure. The change rate of the decrease of Gi slows down gradually after 6 drying–wetting cycles. (3) Under drying–wetting cycles, the ultimate principal stress difference (σ1-σ3)ult meet the normalisation analysis conditions of the weathered red sandstone coarse-grained soil shear stress–shear strain relationship, and the linear normalisation degree of the shear stress–shear strain relationship is high.

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.

Bamboo scrimber beams are prone to brittle failure, and I-shaped steel beams are prone to buckling and out-of-plane instability. To address these issues, the failure process, failure mechanism, deformation and bearing capacity of composite beams made by combining I-shaped steel and bamboo scrimber plates with structural adhesive are studied, taking the shear span ratio ( λ ) as a variable. The failure modes of the composite beam are mainly bottom-up layer-by-layer tearing of the bamboo scrimber and slight out-of-plane deformation of the I-shaped steel in the late loading period. Meanwhile, the ultimate bearing capacity, load‒displacement curve, load–strain relationship and strain distribution of the mid-span section of the composite beams are obtained, indicating that the overall working performance of these beams is excellent and that the comprehensive effect of the components is remarkable. The shear capacity of the composite beam increases with decreasing shear span ratio. By referring to the existing calculation formula of the shear capacity and fitting the test results, we obtain a calculation model of the shear capacity of a composite beam. The average error between the theoretical values and the test values is 11%, indicating that the method can predict the shear capacity well.

With the rapid development of microelectronics packaging technology, the demand for high-performance packaging materials has further increased. This paper developed novel epoxy-containing Sn-3.0Ag-0.5Cu (SAC305-ER) composite solder pastes, and the effects of epoxy resin on their spreading performance, microstructure, and shear behaviour were analysed. The research results showed that with the addition of epoxy resin, SAC305 solder pastes exhibited exceptional spreadability on Cu substrates, which could be attributed to the reduction in the viscosity and the surface tension of the composite solder pastes. With the addition of epoxy resin, the solder matrix microstructure and interfacial morphology of SAC305-ER composite solder joints remained unchanged. However, continuous resin protective layers were observed on the surface of SAC305-ER composite solder joints after the reflow process. The shear properties of the composite solder joints were enhanced by the extra mechanical bonding effect provided by resin layers. When the epoxy resin content was 8 wt%, the shear forces of SAC305-ER composite solder joints reached the maximum value. Fracture analysis indicated that cracked epoxy resin was observed on the surface of SAC305-ER composite solder joints, indicating that the epoxy resin also underwent obvious deformation in the shear test.

Tailings are man-made soils generated by mining activities. When mixed with cement and water, they form a cemented soil called cemented paste backfill (CPB). CPB is commonly used to backfill underground cavities created by ore extraction. The shear behaviour and resistance of the CPB–rock interface are important parameters for the geotechnical design of underground CPB structures. However, CPB can contain a relatively high amount of sulphate, and no studies have been performed to investigate the effect of the initial sulphate content of CPB on the behaviour and resistance of the interface between rock and tailings backfill that is undergoing cementation. The main objective of this experimental investigation is to, therefore, examine the effects of the initial sulphate content (0 ppm, 5,000 ppm, 15,000 ppm, and 25,000 ppm) of CPB on the shear behaviour of the CPB–rock interface at the early ages of curing (1 day, and 3 and 7 days). The obtained results show that, for samples at a very early age of 1 day, an increase in the sulphate content reduces the shear strength of the CPB–rock interface, whereas, for those cured for a longer period of 7 days, the sulphate can either positively or negatively affect the shear strength of the interface depending on the sulphate content.