Full-scale testing of lateral pressures in expansive clay under various saturation conditions is crucial to better understand the behavior of these soils and predict potential damage to structures. However, due to their complexity and cost, only a few full-scale physical testing studies on expansive soils have been reported in the literature. This study aims to provide new insight into the evolution of lateral swelling pressure in expansive soils under infiltration via full-scale physical testing. For this purpose, a heavily instrumented 3-m high masonry wall backfilled with an expansive clay was built and subjected to infiltration. The backfill was compacted in 95% of standard Proctor at a moisture content near optimal to simulate field conditions. The degree of saturation, pore-water pressure, temperature, suction, and lateral and vertical pressures were monitored at different locations during the test. Results showed that the development of lateral pressure is rapid during initial saturation and levels out as the clay approaches saturation levels. This finding highlights the importance of monitoring lateral pressure over time to accurately predict its behavior. The study also found that lateral pressure develops prior to vertical pressure, depending on the area and restraint. The lack of vertical pressure observed during the test is attributed to the continued displacement of the concrete block wall and settlement of the clay with increased area and wet weight of the soil. This finding is important for backfill against basement walls, retaining walls, and foundation units, where the mass of the expansive soil is limited, and effective stress is limited to one dimension.

On December 18, 2023, a destructive M S . 6.2 earthquake occurred in Jishishan County, Gansu Province, China. The earthquake triggered a loess earthflow in Zhongchuan Township, resulting in 13 fatalities. The catastrophic earthflow moved about 3 km without previous rainfall and its mobility index (H/L) is as low as 0.026. We combined multi-source data, including remote sensing images, drone images, and field investigation data, to analyze the mechanism of this disaster. It is found that highly saturated loess liquefied under intense seismic vibration, eventually forming an earthflow and moving rapidly along the northern gully. Moreover, a depth- integrated continuum model that comprehensively considers soil and water lateral pressure is adopted to reveal the above-mentioned mechanism. A MUSCL-HLLC finite volume method with well wet-dry boundary treatment is proposed to solve the full dynamic process of the earthflow. The simulated results reproduce the movement process of this disaster and are in good agreement with the measured data. Compared with other models, the coupling model of soil pressure and water pressure with the partitioned pore water pressure ratio can improve the simulation accuracy. This comprehensive analysis offers valuable insights and guidance for the risk management and prevention of such disasters.

An expansive soil in 4970 special railway line in Dangyang City, China, has encountered a series of landslides due to the expansion characteristics of expansive soil over the past 50 years. Thereafter, a sheet- pile retaining structure was adopted to fortify the expansive soil slope after a comprehensive discussion. In order to evaluate the efficacy of engineering measure of sheet- pile retaining structure, the field test was carried out to investigate the lateral pressure and pile bending moment subjected to construction and service conditions, and the local daily rainfall was also recorded. It took more than 500 days to carry out the field investigation, and the general change laws of lateral pressure and pile bending moment versus local daily rainfall were obtained. The results show that the effect of rainfall on the moisture content of backfill behind the wall decreases with depth. The performance of sheet- pile retaining structure is sensitive to the intensity of rainfall. The arching effect is reduced significantly by employing a series of sheet behind piles. The lateral pressure behind the sheet exhibits a single- peak distribution. The turning point of the horizontal swelling pressure distribution is correlated with the self- weight pressure distribution of soil and the variation of soil moisture content. The measured pile bending moment is approximately 44% of the ultimate pile capacity, which indicates that the sheet- pile retaining structure is in a stable service condition with enough safety reserve.

A great concern for the construction surface cracks of large cross- tunnels, which are being or to be built in the loess strata of China, is attracted. The mechanism of surface crack formation is analyzed from both internal and external perspectives. Loess is a multi-phase porous medium and develops complex stress and strain variation while executing a tunnel project. The surface is highly susceptible to construction surface cracks in shallow sections. A statistical analysis of the constructed loess tunnels in China shows that the main factors affecting surface cracks are settlement deformation, construction scheme, and the surrounding soil environment. To gain an in-depth knowledge of the mechanism of action of factors influencing surface cracks in loess tunnel construction, we relied on the actual project engineering to conduct numerical simulations, which can reproduce the formation mechanism of surface cracks more intuitively. Through numerical simulation, the influence mechanism of tunnel surface cracks under different tunnel diameters, tunnel depths, excavation methods, and surrounding soil grades was obtained. Through the analysis of the factors affecting surface cracks, specific measures to prevent and deal with construction surface cracks are further optimized to provide new ideas for the selection of surface crack control routes in loess tunnels.