Covered sinkhole, due to its hidden, uncertain, and sudden characteristics, often becomes a key and difficult issue in the prevention and control of karst geological disasters. This paper takes the sinkhole in Yaoshan Huamu Farm, Guilin City as an engineering case, and uses field investigation, indoor and outdoor experiments, and theoretical analysis to systematically analyze the main patterns, influencing factors, and evolution laws of sinkhole. The results show that: (1) High-density resistivity tests show that there are many significant low-resistance anomalies at different locations and depths in the study area, indicating that karst fissures are developed in the study area. This is the basic condition for the occurrence of sinkhole. (2) Drilling results show that the groundwater level in the study area is shallow and groundwater is abundant. Groundwater changes the state and strength of the soil, or dissolves the mineral components of the soil layer and dissolves and transports the soil particle aggregates through subsurface erosion and seepage. Therefore, groundwater destroys the soil structure, resulting in the formation of soil caves or sinkholes. (3) Rainfall monitoring shows that the rainy season from May to July each year provides abundant groundwater for the karst area and changes the physical and mechanical properties of the rock and soil mass; while the small rainfall peak around November may trigger the occurrence of sinkhole through mechanisms such as groundwater level fluctuations and enhanced seepage. (4) The vibrations caused by long-term pumping irrigation, surface water leakage, and planting activities in the study area provide important external dynamic conditions for sinkhole. This study can provide theoretical basis and technical support for the prevention and control of collapse disasters in karst areas.

A new type of asphalt pavement disease, known as arch expansion, has appeared in the saline soil regions of Northwest China. The emergence, as well as the evolution of the disease, is strongly related to the distribution of sulfate. However, the decay of Cement-stabilized gravel (CSG) mechanical properties is closely related to the onset and development of arch expansion. The relationship between CSG mechanical strength and salinity in the arch expansion area is analyzed based on field investigations to systematically study the mechanical property degradation law and mechanism of CSG. The mechanical strength and deterioration patterns of CSG with different coupling conditions were investigated. The mineral composition and micromorphology of the erosion products were analyzed. The results show that the mechanical properties of CSG in the area of the arch deteriorate more than those in the regular section. The mechanical strength of the specimens initially containing salt and partially immersed in salt solution decayed most severely. In terms of the deterioration mechanism of mechanical strength of CSG, the water-heat-salt erosion process is also divided into two parts, including the formation stage of gypsum and ettringite, the stage of C-S-H decomposition and thaumasite formation, respectively. The degradation mechanism of CSG is a combination of physical and chemical erosion.

With the increasing demand for large and deep anchor projects in soft soil areas, issues related to settlement in circular foundation pits and damage to supporting structures have become significantly pronounced. The absence of pertinent design methods significantly impacts construction safety. Through on-site monitoring and statistical analysis, this study examines the spatiotemporal evolution of deformation in circular foundation pits, the deformation characteristics of retaining structures, and surface settlement features. Key design factors influencing the stability of circular foundation pits are explored. The research indicates that structural deformation and surface settlement are closely related over time and exhibit substantial spatial coordination. The deformation control capability of circular foundation pits is considerably stronger than that of square foundation pits, and it is less influenced by excavation depth. Diameter and soft soil thickness have a substantial impact on structural deformation and surface settlement. When the diameter is less than 40 m, the structural deformation remains below 0.1%. The study establishes an evaluation method for the deformation control of large and deep circular foundation pits in soft soil based on a significant amount of engineering monitoring data. It categorizes deformation control indicators for pit excavation based on different design factors, offering reliable theoretical support for relevant design professionals.

Magnesium oxychloride cement (MOC) is an environment-friendly cement often used for stabilizing soft soils because of its exceptional mechanical properties. In this study, the influence of curing temperature on the strength development of MOC-solidified clay is explored, considering different MgO/MgCl2 molar ratios. Different tests were carried out to study the corresponding effects. The results show that the effect of curing temperature on the strength of MOC-solidified clay differs greatly from that of cement-solidified soil. Increasing the curing temperature leads to strength reduction, whereas decreasing the curing temperature increases the corresponding strength. Scanning electron microscope (SEM) and X-ray diffraction (XRD) analyses indicate that the variation in type and amount of hydration products of the solidified soil account for the strength development difference between MOC-solidified and cement-solidified soils. A model based on the experimental results is proposed to characterize the relationship between strength development and curing time. The strength influence factor (eta T) and the strength expedite factor (K) were introduced to demonstrate the relationship between strength development at a specific curing temperature as well as at room temperature.