On December 18, 2023, a magnitude MS6.2 earthquake struck Jishishan County, Gansu Province, triggering over 40 seismic subsidence sites within a seismic intensity VI zone, 32 km from the epicenter.The earthquake caused tens of millions in economic losses to mountain photovoltaic power stations. Extensive geological surveys and comparisons with similar landslides (such as soil loosening, widespread cracks, and stepped displacements) triggered by the 1920 Haiyuan MS8.5 earthquake and the 1995 Yongdeng MS5.8 earthquake, this study preliminarily identifies one subsidence sites as a seismic-collapsed loess landslide. To investigate its disaster-causing mechanism: the dynamic triaxial test was conducted to assess the seismic subsidence potential of the loess at the site, and the maximum subsidence amount under different seismic loads were calculated by combining actual data from nearby bedrock stations with site amplification data from the active source; simulation of the destabilization evolution of seismic-collapsed loess landslides by large-scale shaking table tests; and a three-dimensional slope model was developed using finite element method to study the complex seismic conditions responsible for site damage. The research findings provide a theoretical foundation for further investigations into the disaster mechanisms of seismic-collapsed loess landslides.

Post-grouting pile technology has gained extensive application in collapsible loess regions through the injection of slurry to compress and consolidate the soil at the pile base, thereby forming an enlarged base that enhances the foundation's bearing capacity and reduces settlement. Despite the prevalent unsaturated state of loess in most scenarios, the conventional design methodologies for piles in collapsible loess predominantly rely on saturated soil mechanics principles. The infiltration of water can significantly deteriorate the mechanical properties of loess due to the reduction in matric suction and the occurrence of collapsible deformation, leading to a substantial degradation in the bearing behavior of piles. To explore the variations in load transfer mechanisms of post-grouting piles in collapsible loess under conditions of intense precipitation, a comprehensive large-scale model test was conducted. The findings revealed that the post-grouting technique effectively mitigates the adverse effects of negative pile shaft friction in saturated zones on the pile's bearing behavior. Furthermore, the failure criteria for piles may shift from the shear failure of the base soil to excessive pile settlement. By incorporating principles of unsaturated soil mechanics, modified load transfer curves were developed to describe the mobilization of both pile shaft friction and base resistance. These curves facilitate the extension of the traditional load transfer method to post-grouting piles in collapsible soils under extreme weather conditions. The proposed revised load transfer method is characterized by its simplicity, requiring only a few soil indices and mechanical properties, making it highly applicable in engineering practice.

Pile foundations are frequently used in the construction of bridges, offshore platforms, and offshore wind turbines, which are often subjected to complex lateral cyclic loading from wind, wave, or current. These lateral loads usually come from different directions or constantly change their direction, which is ignored by most existing calculation models. A two-dimensional p -y model is proposed in this study for the lateral response of the pile subjected to multi-directional cyclic loading in sand. Without introducing additional parameters, the p -y response in two dimensions is coupled by developing the model within the framework of the bounding surface p -y model. Combined with the collapse and recompression model, the effect of sand collapse around the pile during cyclic loading is considered to approach reality. The pile lateral displacement and soil resistance are obtained in incremental form using the finite difference method in the two-dimensional case. By comparing with the model test results, it is demonstrated that the proposed model is able to reasonably predict the lateral cyclic response of the pile as well as the effects of multi-directional cyclic loading. The distribution and variation characteristics of the soil resistance are further discussed by analyzing the results calculated by the proposed model.

Mesh-free methods, such as the Smooth Particle Hydrodynamics (SPH) method, have recently been successfully developed to model the entire wetting-induced slope collapse process, such as rainfall-induced landslides, from the onset to complete failure. However, the latest SPH developments still lack an advanced unsaturated constitutive model capable of capturing complex soil behaviour responses to wetting. This limitation reduces their ability to provide detailed insights into the failure processes and to correctly capture the complex behaviours of unsaturated soils. This paper addresses this research gap by incorporating an advanced unsaturated constitutive model for clay and sand (CASM-X) into a recently proposed fully coupled seepage flow-deformation SPH framework to simulate a field-scale wetting-induced slope collapse test. The CASM-X model is based on the unified critical state constitutive model for clay and sand (CASM) and incorporates a void-dependent water retention curve and a modified suction-dependent compression index law, enabling the accurate prediction various unsaturated soil behaviours. The integration of the proposed CASM-X model in the fully coupled flow deformation SPH framework enables the successful prediction of a field-scale wetting-induced slope collapse test, providing insights into slope failure mechanisms from initiation to post-failure responses.

Hidden soil caves pose a serious threat to the stability and safety of subgrades. In this study, using the two-dimensional particle flow discrete element code, a total of eight subgrade models with circular soil caves of different dimensions, depths, and locations were established. Under self-weight and superimposed loading, the deformation characteristics of fill subgrade models, such as the evolution of displacement field and crack development process, were analyzed. The results show that under the self-weight, after the fill subgrade model of soil caves with diameters of 2 m, 4 m, 6 m, and 8 m is stable, the overlying soil layer of the soil cave corresponds to the transformation of slag falling, block falling, collapse and rapid collapse, respectively. The larger the dimension of the soil cave, the larger the number of cracks and damage areas, and the more prone the fill subgrade is to collapse. The superimposed load makes the fill subgrade compress from shallow to deep, significantly increasing the overall subgrade deformation, the number of cracks, and the development range. The evolution of the displacement field and crack propagation of the fill subgrade are also controlled by the buried depth and location of the soil cave. Whether the fill subgrade collapses is comprehensively controlled by the dimension and buried depth of the soil cave, the mechanical parameters of the soil layer, the load, and its scope of action. Thus, a comprehensive criterion of cylindrical collapse of the soil layer above the soil cave is constructed.

Malan loess is widely distributed on the Chinese Loess Plateau and poses great challenges to geotechnical, ecological, and agricultural practices due to its unique structure and collapsibility. It is essential to understand the evolution of these properties with depth to assess soil stability and reduce engineering risks in the area. This study investigates the mechanical properties and microstructural evolution of Malan loess with depth and employs multivariate statistical methods to explore their complex interrelationships. Oedometer-collapse tests reveal a 94.2 % reduction in collapsibility coefficient (delta s) from 0.0722 at 1 m to 0.0042 at 9 m, indicating a significant reduction in collapsibility with increasing depth. According to the results of the direct shear test, it showed that the shear strength initially decreases and then increases due to the combined effect of the water content and dry density. Scanning electron microscopy (SEM) images reveal the densification of the loess structure, with changes in particle contact from point to face contact and the evolution from macropores to mesopores and small pores as depth increases. Quantitative analysis by Avzio showed a decrease of 61.5 % in macropores area and an increase of 62.5 % in small pores area. The results obtained by Pearson's correlation analysis and random forest model showed that among these microstructural characteristics, the total pore area (%IncMSE = 22.77 %) is the most important factor influencing the collapsibility properties of loess and water content (%IncMSE = 17.72 %) acts a key role in controlling shear strength. Additionally, compared to traditional methods, the random forest model offers a more insightful understanding of nonlinear relationships and multifactorial coupling effects. These findings provide scientific guidance for geotechnical engineering in loess regions, aiding in risk mitigation and promoting sustainable construction.

Frequent road collapses caused by water leakages from pipelines pose a severe threat to urban safety and the wellbeing of city residents. Limited research has been conducted on the relationship between pipeline leakage and soil settlement, thus resulting in a lack of mathematical models that accurately describe the soil settlement process resulting from water erosion. In this study, we developed an equation for pipeline leakage, conducted physical model experiments on road collapses induced by drainage pipeline leakage, investigated the functional relationship between drainage pipeline leakage and soil settlement, and validated this relationship through physical experiments with pipelines of various sizes. The results indicated that drainage pipeline leakage triggered internal erosion and damaged the soil layers in four stages: soil particle detachment, seepage channel formation, void development, and road collapse. When the pipeline size was increased by a factor of 1.14, the total duration of road collapse induced by pipeline leakage increased by 20.78%, and the total leakage water volume increased by 33.5%. The Pearson correlation coefficient between the theoretical and actual settlement exceeded 0.9, thus demonstrating the reasonableness and effectiveness of the proposed settlement calculation method. The findings of this study serve as a basis for monitoring soil settlement and issuing early road collapse warnings.

On February 6, 2023, two devastating seismic events, the Kahramanmaras, earthquakes, struck the Eastern Anatolian Fault Line (EAF) at 9-h intervals. The first earthquake, with a moment magnitude (Mw) of 7.7, struck the Pazarc & imath;k district, followed by a second earthquake with a moment magnitude (Mw) of 7.6 in the Elbistan district, both within the Kahramanmaras, province. These dual earthquakes directly impacted eleven provinces in Eastern and Southeastern Anatolia leading to significant loss of life and extensive damage to property and infrastructure. This study focuses on revealing the main parameters causing to the collapse of reinforced concrete (RC) buildings by examining their compliance with legislation and earthquake codes in force at the time of construction. For this purpose, detailed examinations such as field observations, collection of general information and official documents about the buildings, determination of material properties and soil characteristics, and three-dimensional finite element (FE) analysis of 400 totally collapsed RC buildings in the Kahramanmaras,, Ad & imath;yaman, Hatay, and Gaziantep provinces, which were among the cities affected by the Kahramanmaras, earthquakes were performed. The findings of this study contribute to a better understanding of the seismic deficiencies of buildings in earthquake-prone regions and provide information on which strategies to develop to increase the resilience of buildings with similar characteristics in other earthquake regions against future seismic events. Considering that the time from the beginning of the construction of the building until its completion consists of several stages, it can be seen that 43.58 % of the errors that cause damage and collapse of the buildings in this study are made in the construction stage, 25.57 % in the FE analysis stage, 24.77 % in the license stage, and 6.07 % in the after construction stage. Thanks to the development process of earthquake codes, regulations in building inspection practices and easier access to quality materials have greatly reduced the damage and collapse of buildings constructed in recent years.

This paper aims to investigate the tunnelling stability of underwater slurry pressure balance (SPB) shields and the formation and evolution mechanisms of ground collapse following face instability. A laboratory SPB shield machine was employed to simulate the entire tunnelling process. Multi-faceted monitoring revealed the responses of soil pressure, pore water pressure, and surface subsidence during both stable and unstable phases. The morphological evolution characteristics of surface collapse pits were analyzed using three-dimensional scanning technology. The experimental results indicate that: (1) The key to stable tunnelling is balancing the pressure in the slurry chamber with the tunnelling speed, which ensures the formation of a filter cake in front of the cutterhead. (2) The torque of the cutterhead, soil pressure, and surface subsidence respond significantly and synchronously when the tunnel face becomes unstable, while the soil and water pressures are relatively less noticeable. (3) Excavation disturbance results in a gentler angle of repose and a wider range of collapse in the longitudinal direction of the collapsed pit. (4) A formula for predicting the duration of collapse is proposed, which effectively integrates the evolution patterns of the collapse pit and has been well-validated through comparison with the experimental results. This study provides a reference for the safe construction of tunnel engineering in saturated sand.

The leakage of drainage pipes is the primary cause of underground cavity formation, and the cavity diameter-to-depth ratio significantly affects the overall stability of roads. However, studies on the quantitative calculation for road comprehensive bearing capacity considering the cavity diameter-to-depth ratio have not been extensively explored. This study employed physical model tests to examine the influence of the cavity diameter-to-depth ratio on road collapse and soil erosion characteristics. Based on limit analysis theorems, a mechanical model between the road comprehensive bearing capacity and the cavity diameter-to-depth ratio (FB-L model) was established, and damage parameters of the pavement and soil layers were introduced to modify the FB-L model. The effectiveness of the FB-L model was validated by the data derived from eight physical model tests, with an average deviation of 14.0%. The results indicate a nonlinear increase in both the maximum diameter and fracture thickness of the collapse pit as the cavity diameter-to-depth ratio increased. The pavement and soil layers adjusted the diameter and fracture thickness of the collapse pit to maintain their load-bearing capacity when the cavity diameter-to-depth ratio changed. The fluid erosion range increased continuously with increasing depth of buried soil and was influenced predominantly by gravity and seepage duration. Conversely, the cavity diameter decreased as the buried depth increased, which is associated with the rheological repose angle of the soil. Furthermore, the damage parameters of the pavement and soil layers decrease as the distance from the collapse pit diminishes, with the pavement exhibiting more severe damage than the soil layer. This study provides a theoretical basis for preventing road collapses.