Bedrock-soil layer slopes (BSLSs) are widely distributed in nature. The existence of the interface between bedrock and soil layer (IBSL) affects the failure modes of the BSLSs, and the seismic action makes the failure modes more complex. In order to accurately evaluate the safety and its corresponding main failure modes of BSLSs under seismic action, a system reliability method combined with the upper bound limit analysis method and Monte Carlo simulation (MCS) is proposed. Four types of failure modes and their corresponding factors of safety (Fs) were calculated by MATLAB program coding and validated with case in existing literature. The results show that overburden layer soil's strength, the IBSL's strength and geometric characteristic, and seismic action have significant effects on BSLSs' system reliability, failure modes and failure ranges. In addition, as the cohesion of the inclination angle of the IBSL and the horizontal seismic action increase, the failure range of the BSLS gradually approaches the IBSL, which means that the damage range becomes larger. However, with the increase of overburden layer soil's friction angle, IBSL's depth and strength, and vertical seismic actions, the failure range gradually approaches the surface of the BSLS, which means that the failure range becomes smaller.

Underground structures may be buried in liquefiable sites, which can cause complex seismic response mechanisms depending on the extent and location of the liquefiable soil layer. This study investigates the seismic response of multi-story underground structures in sites with varying distributions of liquified soil employing an advanced three-dimensional nonlinear finite element model. The results indicate that the extent and location of liquefied soil layers affect the seismic response characteristics of underground structures and the distribution of their damage. When the lower story of the subway station is buried in liquefied interlayer site, the structure experiences the most serious damage. When the structure is located within a liquefiable interlayer site, the earthquake ground motion will induce greater inter-story deformation in the structure, resulting in larger structural residual displacement. When all or part of the underground structure is buried in the liquefiable soil layer, the structural failure mode should be assessed to ensure that the underground rail transit can quickly restore functionality after an earthquake. Meanwhile, permeability effects of liquefiable soil have a significant impact on the dynamic response of subway station in the liquefiable site.

Gravel-bearing sandstone reservoirs represent a significant type of reservoir in oil and gas exploration. Due to the difference of the spatial random distribution the content and the shape of the gravel particles, these reservoirs exhibit complex mechanical properties and failure modes. In this study, a numerical model of gravel-bearing sandstone was developed by using the Finite Element Method (FEM) and were verified by the actual indoor experimental data. The effect of the gravel particle sizes, gravel content, and gravel types on the compressive peak strength and microcrack evolution processes are further analyzed. The results reveal that cracks initiate within the sandstone matrix surrounding the gravel and propagate through the gravel with continued loading. The primary factors governing the stability of gravel-bearing sandstone are the gravel radius and content. The variation in gravel penetration rate is synchronized with the changes in peak strength. By embedding gravel particles of different shapes into the model, it is observed that the peak compressive strength of round gravel is comparable to that of elliptical gravel, with both exhibiting higher peak strengths than angular gravel. Regression models demonstrate that the tensile strength difference between the gravel and the sandstone matrix is a critical parameter influencing gravel penetration. Confining pressure has a relatively minor effect on the elastic modulus, while its impact on peak compressive strength is significantly more pronounced.

Loess disaster chains on the Heifangtai Platform, China, cause frequent loess landslides and form landslide dams, thus obstructing rivers. In addition, the failure of landslide dams causes loess mudflows and other related disasters. In this study, the influences of different inflow rates on the failure process and triggering mechanisms of loess landslide dams were explored using five sets of model experiments. These experimental results revealed that the failure of loess landslide dams occurs through overtopping and piping failure, or overtopping failure. Overtopping and piping failure can be divided into infiltration, seepage channel development, break overflow, and rebalancing. When the inflow rate was 1.0 L/s, the water could not penetrate the dam in time. Overtopping failure primarily involves horizontal and downward erosion of the breach. The inflow rate was positively correlated with soil transport, peak flow velocity, and peak bulk density based on the experimental data. The bulk density of the failure mudflow was categorized into slow increase, transition, and attenuation stages based on our experimental results. In addition, by analyzing the volume and stability of residual dams, the likelihood and damage degree of secondary hazards after the dam failure were initially explored. This study provides a scientific basis for relevant studies on loess landslide dam failure.

In the construction of cold region engineering and artificial freezing engineering, soil-rock mixture (SRM) is a frequently encountered geomaterial. Understanding the mechanical properties of frozen SRM is crucial for ensuring construction safety. In this paper, frozen SRM is considered as a multiphase material consisting of a soil matrix and rock. By employing a single-variable approach, the relationship between UCS and rock content was revealed, and the effects of rock content on the stress-strain curve shape and failure mode were analyzed. The test results indicate that rock content significantly influences the stress-strain curve and failure mode of SRM. The specimen preparation with different rock content is unified using a given relative compactness. The uniaxial compressive strength (UCS) of the frozen specimens increases firstly and then decreases as rock content increases, which is unaffected by temperature or rock size. The classic quadratic polynomial is suggested to describe the variation rule. The failure modes of specimens with low, medium and high rock content correspond to shear failure, bulge failure and splitting failures, respectively, which transmits from shear failure to splitting failure as the rock content increases.

Tensile cracks play a pivotal role in the formation and evolution of reservoir landslides. To investigate how tensile cracks affect the deformation and failure mechanism of reservoir landslides, a novel artificial tension cracking device based on magnetic suction was designed to establish a physical model of landslides and record the process of landslide deformation and damage by multifield monitoring. Two scenarios were analyzed: crack closure and crack development. The results indicate that under crack closure, secondary cracks still form, leading to retrogressive damage. In contrast, under crack development conditions, the failure mode changes to composite failure with overall displacement. The release of tensile stresses and compression of the rear soil are the main driving forces for this movement. Hydraulic erosion also plays a secondary role in changing landslide morphology. The results of multifield monitoring reveal the effects of tensile cracking on reservoir landslides from multiple perspectives and provide new insights into the mechanism of landslide tensile-shear coupled damage.

Safety assessment of ductile iron (DI) pipelines under fault rupture is a crucial aspect for underground pipeline design. Previous studies delved into the response of DI pipelines to strike-slip faults, but all existing theoretical methods for DI pipelines under strike-slip faults are not suitable for normal fault conditions due to the difference in soil resistance distribution. In this study, analytical solutions considering asymmetric soil resistance and pipe deflection are developed to analyze the behavior of DI pipelines under normal faulting. Results indicate that DI pipelines with a longer segment length are more vulnerable to pipe bending damage, while exhibiting a lower sensitivity to joint rotation failure. For the conditions of pipe segment length L = 1.5 m at all burial depths and L = 3 m at a shallow burial depth, when the fault-pipe crossing position shifts from a joint to a quarter of the segment length (rp = 0 similar to 0.25), DI pipelines are more prone to joint rotation failure. However, in the cases of L = 3 m at a moderate to deep burial depth and L = 6 m at all burial depths, the most unfavorable position is rp = 0.75, dominated by the mode of pipe bending failure.

Initial damage is a significant factor leading to alterations in the mechanical properties of discarded tire materials. With reinforced soil being at its serviceability limit state, the one-dimensional tensile stress state predominates within the reinforcement material. The tensile properties of tire-derived geotechnical reinforcement material(TGRM) with initial damage directly determine whether the reinforcement effect can stably exist within the reinforced soil. To investigate the tensile properties, damage mechanisms, and the relationship between the failure mode of TGRM and its absorptive capacity for strain energy under initial damage conditions, static tensile tests were conducted to obtain the stress-strain relationships, post-fracture elongation rates and fracture morphologies of both strip-shaped and ring-shaped TGRM. During the tensile process, research indicates that the non-zero-degree steel fibers within TGRM undergo a symmetrical interlaminar relative displacement. This ensures that the cross- remains macroscopically planar throughout, ultimately leading to a interlayer cracking in the belt layers. Prior to the cracking, a reliable anchoring relationship constantly exists between the steel fibers and the rubber matrix. Initial damage determines the integrity of zero-degree belt layer and the depth of non-zero-degree steel fibers embedded into the rubber matrix, which in turn affects the strain energy storage capacity and the failure mode of TGRM. The results may provide references for the establishment of the constitutive relationship and strength theory of TGRM under initial damage conditions.

This study systematically examines the influence of joints on the mechanical properties of loess, highlighting the impact of joint dip angles on soil deformation and failure mechanisms. By employing an innovative layered compaction method to prepare jointed specimens, and conducting comparative experiments with different simulation materials (wax paper, rice paper, and plastic film), a series of controlled indoor triaxial compression tests were performed. The key findings are as follows: (1) The joint dip angle plays a decisive role in the evolution of failure mode, with five typical failure mechanisms identified based on fracture characteristics: shear failure, sliding failure, conjugate shear failure, sliding-shear failure, and sliding-conjugate shear failure. (2) The weakening effect of joints exhibits confining pressure dependency: Under low confining pressure (50 kPa), jointed specimens demonstrate increased axial displacement and a reduced shear strength attenuation ratio. (3) Mechanical parameters are significantly influenced by the dip angle: When the joint dip angle falls within the critical dip range of 60 degrees-75 degrees, both cohesion and internal friction angle reach their minimum values, forming zones of weakened mechanical properties. (4) A comparative analysis of simulation materials indicates that single-layer rice paper, due to its optimal thickness and tensile strength, effectively replicates the contact behavior of natural joint surfaces. This study establishes the quantitative relationship between joint geometric parameters and mechanical responses, providing an experimental basis for the engineering geological assessment of loess.

Granite residual soil exhibits a tendency to collapse and disintegrate upon exposure to water, displaying highly unstable mechanical properties. This makes it susceptible to landslides, mudslides, and other geological hazards. In this study, three common biopolymers, i.e., xanthan gum (XG), locust bean gum (LBG), and guar gum (GG), are employed to improve the strength and stability of granite residual soil. A series of experiments were conducted on biopolymer-modified granite residual soil, varying the types of biopolymers, their concentrations, and curing times, to examine their effects on the soil's strength properties and failure characteristics. The microscopic structure and interaction mechanisms between the soil and biopolymers were analyzed using scanning electron microscopy and X-ray diffraction. The results indicate that guar gum-treated granite residual soil exhibited the highest unconfined compressive strength and shear strength. After adding 2.0% guar gum, the unconfined compressive strength and shear strength of the modified soil are 1.6 times and 1.58 times that of the untreated granite residual soil, respectively. Optimal strength improvements were observed when the biopolymer concentration ranged from 1.5% to 2%, with a curing time of 14 days. After treatment with xanthan gum, locust bean gum, and guar gum, the cohesion of the soil is 1.36 times, 1.34 times, and 1.55 times that of the untreated soil, respectively. The biopolymers enhanced soil bonding through cross-linking, thereby improving the soil's mechanical properties. The gel-like substances formed by the reaction of biopolymers with water adhered to encapsulated soil particles, significantly altering the soil's deformation behavior, toughness, and failure modes. Furthermore, interactions between soil minerals and functional groups of the biopolymers contributed to further enhancement of the soil's mechanical properties. This study demonstrates the feasibility of using biopolymers to improve granite residual soil, offering theoretical insights into the underlying microscopic mechanisms that govern this improvement.