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.

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.

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.

The weak mechanical properties of weak interlayers are crucial for controlling landslide deformation and failure under water level fluctuation. The instability and failure of landslides in reservoirs can lead to unpredictable consequences. In this study, the reservoir bank landslide with a weak interlayer was selected as the research subject. The material composition, structural characteristics, mechanical properties, and permeability of the landslide were determined through field investigations and tests. Additionally, a physical model test was conducted to explore the groundwater variation rules and deformation failure modes of landslides with weak interlayers under different water level fluctuation rates. The results indicate that due to the low permeability of the interlayer, there was a significant lag in monitoring data such as pore water pressure within the interlayer under the same water level fluctuation rate. At the same point, the faster the water level fluctuation rate, the greater the degree of lag. The deformation and failure mode of landslide with weak interlayer under reservoir water level fluctuation can be summarized as the following five stages: slope toe erosion stage, cracks on slope surface and interlayer stage, micro-collapse of slope toes and crack expansion of slope surface and interlayer stage, local micro-collapse of slope toe and crack penetration of slope body stage, crack development leads to landslide of slope body stage. This study provides theoretical support for prevention and control of landslides with weak interlayers in the gravel soils of reservoirs.

Effective identification of damage characteristics and failure modes for buried pipelines subjected to fault movements is crucial for early design and disaster assessment. In the preceding companion paper, the structural responses of large-diameter prestressed concrete cylinder pipeline (PCCP) subjected to fault displacement were initially investigated under the condition where faulting crosses pipe barrel vertically, and the deterioration process and failure modes were summarized. However, the structural responses of jointed pipelines are closely tied to faulting parameters. In this paper, a study on the location and angle of the fault plane is conducted, and the damage response and failure modes of large-diameter PCCPs are analyzed in detail and compared. The results show that strike-slip fault movement causes pipeline movement through pipe-soil interaction, and the fault displacement is accommodated by several pipe segments for the large diameter-to-length ratio PCCPs. When the fault plane crosses the pipe segment at an acute angle, the primary failure modes include material damage to the pipe joints and barrel, as well as the risk of joint leakage. Material damage occurs at the joint when the fault plane passes through the PCCP joint. Given the mechanical properties and seismic resilience of PCCPs, it is advisable to avoid faulting at acute angles crossing pipeline joints. This work focuses on the structural behavior of segmented composited PCCPs crossing a fault, aiming to predict pipeline damage and failure. The findings contribute to a comprehensive understanding of the failure modes, damage characteristics, and disaster evaluation of PCCPs under strike-slip fault conditions.

To clarify the effect of various anchor cable failure modes on the dynamic responses of slopes, the FLAC3D software was redeveloped. Constitutive models of cable elements in different anchor cable failure modes were proposed and embedded into the main program of slope dynamic calculation. The axial force, acceleration, and displacement responses in different anchor cable failure modes were compared and analyzed. The effects of seismic parameters on the anchor cable failure modes were also investigated. A matching relationship between the ultimate load-bearing capacities of the anchorage, anchoring interface, and tendon was proposed. The results reveal that the seismic intensity causing anchor cable damage in anchorage failure mode (AFM) and grouting body failure mode is 0.2g-0.3 g lower than that in tendon failure mode. At the moment of failure, the stress released by the anchor cable in AFM is the highest, with the most evident instantaneous slope acceleration fluctuation. In the collaborative seismic design of the anchorage, anchoring section, and anchor tendon, the ultimate load-bearing capacities of the anchorage and anchoring interface should be increased by 1.8 times to match the tensile bearing capacity of the tendon. This study provides a reference for the seismic anchorage design of slopes and offers suggestions for selecting seismic design parameters for anchor cables.

Forests play an important role in controlling the formation and movement processes of debris flows. They contribute to soil stabilization, regulation of soil water content, and act as robust structures impeding the downstream progression of debris flows. On the positive side, trees, to some extent, can intercept debris flows and effectively mitigate their velocity by increasing flow resistance. On the negative side, trees may suffer damage from debris-flow hazards, characterized by the generation of substantial quantities of wood fragments and consequential ramifications such as river channel blockage, resulting in backwater rise. In extreme cases, this blockage collapse can lead to instantaneous discharge amplification, thereby adversely impacting urban safety and impeding sustainable development. Therefore, in order to grasp the effects of tree characteristics on tree failure modes, the tree failure modes and corresponding parameters, diameters at breast height (DBH) and root-soil plate size, were identified and recorded through the post-event field investigation in Keze Gully, a region prone to debris-flow events in Sichuan, China, respectively. To investigate the impact of spatial variability in tree root distribution on tree failure modes, the root cross-sectional area ratio (RAR), root density (RD), root length density (RLD) and soil detachment rate (SDR) were obtained. The findings indicated that: (1) Tree characteristics reflect the interactions of debris flows and trees, and influence the tree failure modes ultimately. The root distribution characteristics influence the size and shape of the root-soil plate to affect the resistance of trees. (2) Compared to burial and abrasion, stem breakage and overturning are the predominant modes of tree failure in debris-flow hazards. Trees with a smaller DBH primarily experience stem breakage and bending, and trees with a larger DBH mostly experience overturning. (3) The root-soil plate shapes of overturned trees, affected by the root architecture and root growth range, are generally semielliptical or semicircular, and the horizontal and vertical radii increase with DBH, but the correlation between the root-soil plate's breadth-depth ratio and DBH is low. (4) The biomass and RAR decrease with distance. The RAR distribution exhibit the order of upslope direction > downslope direction > lateral direction. The coarse root biomass significantly increases with DBH, but no clear trend in fine root biomass. (5) The roots can significantly enhance the soil erosion resistance, but the erosion resistance of coarse roots is not as significant as that of fine roots. The erosion resistance increases with DBH, and follows the order of upslope direction > downslope direction > lateral direction. The results could provide new insights into the influences of tree and root distribution characteristics on tree failure modes during debris flows.

The formation of multi-layer horizontal ice lenses in frozen soil significantly alters its internal structure, leading to changes in its mechanical properties. To quantitatively analyze the effects of multi-layer ice lenses on mechanical properties, a series of freezing tests were conducted with frost-susceptible clay materials at varied freezing ratios. Then, the uniaxial compression tests were conducted to investigate the deformation and strength properties of frozen soil at different freezing ratios and temperatures. The experimental results indicate that the unique ice skeleton structure formed by horizontal ice lenses and inclined ice wedges can significantly improve the strength of the samples, leading to the peak stress and secant modulus E-50 increase with the freezing ratio, and the presence of an ice skeleton makes the strength more sensitive to temperature changes. The frozen soil samples exhibit two failure modes (bulging failure and shearing failure), which significantly affect the mechanical parameters of the soil. Based on the test results, a frost heave-induced damage coefficient is introduced into the strain softening model to account for the initial stiffness reduction caused by microcracks generated during the ice skeleton growth. This modified model effectively predicts the stress-strain relationship of soils with varying ice skeleton structures. These findings have practical implications for predicting the properties of frozen soil constructed using artificial freezing methods.

Understanding the failure process of bottom-saturated loess slopes is of great significance in loess areas where flood irrigation is commonly utilized to alleviate the scarcity of precipitation. In this study, the failure process of a loess slope with an increased groundwater level was recreated and the multiple failure modes of loess landslides were revealed. A centrifugal model test was conducted using a groundwater-recharge device. An intact loess sample retrieved from the Heifangtai Loess Terrace was employed in the test. The model test was monitored using a video recorder, high-speed camera, and soil/pore water pressure sensors, and the results were validated by utilizing an intermittently investigated field landslide. Based on the monitored data and acceleration, the test was divided into three periods: the initial acceleration period with no water inlet (0-40 g), bottom saturation period (40-60 g), and failure occurrence period (60-80 g). The soil/ pore water pressure and degree of deformation were relatively low, with a steadily increasing trend during the first two periods. With the enrichment of the soil water content, retrogressive sliding, deep subsidence, and surface sinkhole failures occurred successively up to areas with relatively high pore water pressure during the last period. The results of the field landslide investigation showed multiple failure modes, as observed in the model test. The results suggest that the coexistence of multiple failure modes could gradually evolve into croplands and promote water infiltration into the deep loess, increasing the groundwater level and accelerating the failure process of the slope. Despite the overall effects of multiple failure patterns on the evolution of the slope, each failure pattern had a relatively independent evolutionary process within a certain area, which could be further analyzed for the early recognition of loess landslides. This study also indicates that the challenges of centrifuge modeling for water-related materials with intact soil samples are the boundary conditions and data monitoring within the model.

Flooding occurrences have become increasingly severe, posing a serious danger to end-user safety and bridge resilience. As flood fragility assessment is a valuable tool for promoting the resilience of bridges to climate change, it is of great importance to push the development of such methods. However, flood fragility has not received as much attention as seismic fragility despite the significant amount of damage and costs resulting from flood hazards. There has been little effort to estimate the flood fragility of bridges considering various flood-related factors and the corresponding failure modes. To this end, a fragility-based approach that can explicitly address the scour-hole geometry and flood-induced lateral load is presented. First, a three-dimensional finite-element model with pile foundations and surrounding soil was established to estimate the failure mode under various flood scenarios. The loadings on pile foundations were characterized by vertical loading from the superstructure, horizontal loading from the flood-induced lateral load, and the scour effect simulated through a time-history analysis. Then, all potential failure modes of bridge pile foundations in various flood scenarios were summarized. Based on extensive parameter investigations using the deterministic method, the dominant failure mode of penetration failure was determined, and a failure envelope was fitted to guide the design of the pile foundation. Upon establishing the failure mode, a probabilistic fragility analysis considering uncertainties in hydraulic, structural, and geological parameters was finally conducted using the Latin hypercube sampling (LHS) method. The results showed the effects of variation on the fragility of the pile foundation, highlighting that the deterministic analysis without considering the uncertainties in model parameters leads to underestimating the risk due to the penetration failure and the significant influence region.