This paper proposes a carbon fiber reinforced polymer (CFRP) retrofitting scheme for improving the seismic performance of atrium-style metro stations (AMS). Past experimental studies have confirmed that the weakest of the AMS during strong earthquakes is located at the upper-story beam ends. However, there is thus far no candidate for a reference approach to retrofitting and strengthening the AMS. This study addresses this gap by applying CFRP retrofitting to both ends of the upper-story beam. The main objective is to assess the effectiveness of the proposed retrofitting scheme. First, a three-dimensional finite element model is developed to simulate dynamic soil-AMS interaction. The validity of the numerical method is assessed via a comparison with measured data from reduced-scale model tests. Second, a numerical model of the AMS retrofitted with CFRP is built using validated methods. Finally, dynamic time-history analyses of the AMS with and without CFRP retrofitting are conducted, and their dynamic responses, including inter-story drift, dynamic strain, and tensile damage, in conjunction with the lateral displacement of the surrounding ground, are compared. Comparison of the results for the non-retrofitted and retrofitted structures shows that CFRP retrofitting significantly reduces both the principal strains and tensile damage factors at the upper-story beam ends while slightly increasing those values at the mid-span of the beam; additionally, it does not change the structural lateral deformation. Therefore, it can be concluded that CFRP retrofitting could effectively improve the seismic performance of the AMS without changing its lateral stiffness.

Large-span corrugated steel utility tunnels are widely used owing to their large spatial spans and excellent mechanical properties. However, under seismic forces, they may experience significant deformation, making repair challenging and posing a serious threat to personal safety. To study the seismic performance of corrugated steel utility tunnels, an equivalent orthotropic plate was introduced, and a simplified three-dimensional refined finite element model was proposed and established. Considering the site conditions of the structure, the structural parameters, and different seismic input conditions, a detailed analysis was conducted using the endurance time analysis method. The results indicated that the simplified model agreed well with the experimental results. The seismic input conditions significantly affected the relative deformation of the structure. Under the action of P waves (compression waves) and P + SV waves (compression and shear waves), the deformation of the upper part of the structure was relatively uniform, whereas under the action of SV waves (shear waves), the deformation of the crown was more evident. The greater the burial depth of the structure, the stronger the soil-structure interaction, and the smaller the increase in relative deformation. In soft soil, the structure was more likely to be damaged and should be carefully observed. Additionally, increasing the corrugation profile of the steel plates during the design process was highly effective in enhancing the overall stiffness of the structure. Based on the above calculation results, the relative deformation rate was proposed as a quantitative index of the seismic performance of the structure, and corresponding values were recommended.

Volume changes in soil caused by freeze-thaw cycles can affect the shear performance of the saline soil-geotextile interface. To investigate this issue, the study examined changes in shear strength, deformation characteristics, and failure modes of the saline soil-geotextile interface under different numbers of freeze-thaw cycles. The experimental results indicate that with the increase in freeze-thaw cycles, the shear stiffness of the interface initially increases and then decreases, demonstrating the reduction in elasticity and resistance to deformation caused by freeze-thaw cycles. And the enhancement of normal stress can effectively increase the density of the soil and the adhesion at the interface, thereby improving shear stiffness. Meanwhile, the salt content in the soil also significantly impacts the mechanical properties, with notable changes in the dynamic characteristics of the interface as the salt content varies. Furthermore, after freeze-thaw actions, the soil becomes loose, reduces in integrity, features uneven surfaces, and sees increased internal porosity leading to slip surfaces. Trend analysis from this study provides new insights into the failure mechanisms at the saline soil-geotextile interface.

The instability and collapse mechanisms of tunnels in deep-buried marine soil-rock mixture (SRM) strata remain poorly understood, posing significant challenges to engineering safety. This study employs a discrete element method (DEM) to establish an S-RM model, integrating ball particles and rblock blocks to simulate soil and rock, respectively. The deformation evolution, shear band formation, porosity variation, force chains, and anisotropy of S-RM under varying stress release rates are systematically investigated, with emphasis on rock content, water content, and rblock types (rubble and cobble). The results reveal that tunnel excavation reduces radial interparticle contact forces, inducing convergent squeezing deformation, while tangential forces increase, forming a soil arch dominated by horizontal force chains. Higher rock content enhances shear resistance and accelerates soil arch formation but intensifies dilatancy under high stress release, expanding collapse zones. Elevated water content increases lateral pressure coefficients, promoting earlier arch formation, yet reduces interparticle bond strength and rock anti-slip capacity, leading to premature shear failure. Cobbles, whose long axis tends to rotate in the slip direction, exhibit weaker shear resistance and lower dilatancy than rubble, thereby increasing soil arch instability. Crucially, shear band evolution and force chain fracture at side walls disrupt arch integrity, triggering progressive collapse. These micro-mechanisms elucidate the coupled effects of stress redistribution, particle interactions, and material heterogeneity on S-RM failure. Suggestions for construction control include minimizing excavation footage, implementing timely support, and reinforcing sidewalls with feet-lock bolts to stabilize soil arches. This work advances the theoretical framework for disaster mitigation in deep-buried S-RM strata, offering a DEMbased paradigm for predicting and controlling tunnel instability.

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.

This paper investigates the pullout behaviours of horizontal rectangular plate anchors under inclined loading in sand using three - dimensional finite element (3D-FE) analysis. An advanced bounding surface plasticity model incorporating the critical state framework is developed to capture the stress-strain relationship of sand. The model is firstly validated against various analytical solutions and centrifuge test data. Then, a series of FE analysis is conducted to consider the effects of plate anchor aspect ratio, initial embedment depth, sand relative density and inclined loading angle on the pullout capacities. Results show that shallow anchors develop failure zones reaching the soil surface, and vertical pullout capacity exceeds that under pure vertical loading when the load is slightly inclined. For deep anchors, failure zones are confined below the surface, and horizontal pullout capacity exceeds that under pure horizontal loading when the load is slightly inclined. The transitional embedment depth depends on anchor aspect ratio and sand density. A modified analytical solution is proposed to estimate the vertical pullout capacity of plate anchors from shallow to deep depths. Failure envelopes established from probe tests provide practical guidance for assessing rectangular anchor failures under various inclined loadings.

Rainfall-induced debris slides are a major geological hazard in the Himalayan region, where slopes often comprise heterogeneous debris-a complex mixture of rock and soil. The complex nature makes traditional soil or rock testing methods inadequate for assessing such debris's engineering behaviour and failure mechanisms. Alternatively, reduced-scale flume experiments may aid in understanding the failure process of debris slopes. Here, we present findings from reduced-scale laboratory flume experiments performed under varying slope angles (ranging from shallow to steep), initial volumetric water contents (ranging from dry to wet), and rainfall intensities (ranging from light to heavy) using debris materials with a median grain size (D50) 20.7 mm sampled from a rainfall-induced debris slide site in the Himalayas. Hydrological variables, including volumetric water content and matric suction, were monitored using sensors, while slope displacement was tracked indirectly, and rainfall was monitored using rain gauges. The entire failure process was captured via video recording, and index and shear strength tests were performed to characterize the debris material. Our results reveal that the failure of debris slopes is not driven by sudden increases in pore water pressure but by the loss of unsaturated shear strength due to reduced matric suction and a decreased frictional strength from reduced particle contact between grains during rainfall. We also find that the saturation of debris slope by rainfall was quick irrespective of the slope angles and initial moisture contents, revealing the proneness of debris slopes to rainfall-induced failures. These findings provide critical insights into the stability of debris materials and have important implications for improving risk assessment and mitigation strategies for rainfall-induced debris slides in the Himalayas and similar regions worldwide.

Earthquakes and rainfall both cause soil damage and strength degradation of cutting slopes, resulting in increased slope instability. However, few studies have been conducted on the failure mechanisms of cutting slopes under earthquakes and rainfall. In this study, field electrical measurements were conducted to evaluate the damage to a cutting slope hit by the Yangbi Earthquake (MS = 6.4) in Yunnan Province, China. After material segmentation using the resistivity probability density statistical method, we observed several damaged areas running along the slope depth direction, forming several potential sliding surfaces. Furthermore, considering the slope damage after the earthquake, a discrete element model of the slope was developed, and the dynamic process of the gravel-soil landslide under rainfall was analyzed. Compared with low cutting slope with thin overburden sliding along one sliding surface, the results indicate that the high cutting slope with thick overburden slides along several sliding surfaces that formed by the earthquake-step sliding mods. Slope sliding can be divided into four stages: First, the slope body at the bottom area slid and accelerated firstly, while several cracks appear on the top area due to tension (initial stage and acceleration stage). Thereafter, the upper slope body gradually slides along its respective sliding surface. The body at the bottom area of the slope was pushed by that at the upper area and slid at a high velocity along the sliding surfaces due to secondary acceleration (secondary acceleration stage). Finally, the sliding velocity of the slope gradually decreases, and an accumulation is formed, entering a stable stage (deceleration stage).

The experimental studies were performed to examine the failure mechanism and the capacity of BFRP bolt-anchorage system under laboratory and field conditions in supporting clay slopes in Sichuan Basin, China. The results indicate that BFRP anchor bolts, designed based on the principle of equal strength replacement between bolt tensile strength and the bonding strength of the first interface, can meet the safety standards required for slope engineering. During the stable phase of the slope, the mechanical behavior and deformation characteristics of BFRP anchor bolts are comparable to those of steel anchor bolts, with the axial force of BFRP bolts being 1/3 to 1/4 lower than the designed value. When the slope enters the accelerated creep stage, the axial force of steel anchor bolts exceeds the designed value by 40 %, while the axial force of BFRP bolts remains at only 2/3 of that of steel bolts. The failure mechanisms of the BFRP bolt-anchorage system primarily involve shear failure at the bolt-mortar interface and pullout failure of the bolt body, which are attributed to the cumulative damage of the polymer material. Based on the experimental findings, it is recommended that the minimum tensile safety factor for BFRP bars used in temporary slope support should be set at 1.26. This study enhances the understanding of BFRP anchorage systems in clay soil environments and provides valuable insights for the design and construction of infrastructure projects in similar geological conditions.

In this paper, the Huangtupo Riverside Slump 1#, a reservoir landslide with double sliding zones in the Three Gorges Reservoir Area of China, is selected as the prototype for a scaled physical model test subjected to water level fluctuation and rainfall. The spatial-temporal characteristics of the multi-physical monitoring data are thus obtained, including the pore water pressure, earth pressure, surface deformation, and deep deformation. Subsequently, the failure mechanism and evolution process of the landslide model are discussed. The results indicate that the rise and fall of reservoir water correspondingly increase and decrease the pore water pressure and earth pressure at the front edge of the model, while having almost no effect on the trailing edge. The rainfall increases the pore water pressure and soil pressure of the entire model, and the increase is proportional to its duration and intensity but limited by the height of overlying soil. Both the surface deformation and deep deformation increase with the fall of reservoir water and rainfall. Except for the weakening effect of the soil caused by the first rise of reservoir water, which results in a certain surface deformation and deep deformation, the surface deformation has almost no response with the subsequent rises, while the deep deformation decreases with the rises. The Riverside Slump 1-1# exhibits the characteristics of retrogressive failure with whole evolution phases, while the Riverside Slump 1-2# exhibits a composite evolution, in which its middle front belongs to the retrogressive failure within the initial deformation, and the trailing edge belongs to the progressive failure within the accelerated deformation.