Dynamic response and macro-micro characteristics of red soil in shallow karst collapse area along the railway

Karst collapse as a unique environmental geological hazard in karst areas, easily causes changes in surrounding water and soil environments. Train-induced vibration is a significant inducement for shallow karst ground collapse. Previous studies on the dynamic properties of surrounding soil under train vibration loads often neglected the impact of time intermittent effects. Taking the red soil covering a typical potential karst collapse area along a high-speed railway in China as the research object, field monitoring of the vibration characteristics of the surrounding environment was conducted. A series of continuous loading and continuous-stop-continuous dynamic triaxial tests and scanning electron microscopy (SEM) tests were designed considering factors such as loading frequency, intermittent duration, and dynamic stress amplitude. The effects of loading intermittence on the dynamic response and microstructure of red soil were compared and analyzed. The experimental results show that the drainage and unloading of red soil samples during the intermittent phase dissipate the accumulated excess pore water pressure and adjust the internal particle and structure of the soil, reducing the accumulation of plastic deformation during subsequent loading stages. The residual strain under vibration loading conditions considering the time intermittent effect is significantly reduced, and the residual strain decreases significantly with the increase of time intervals. The weakening effects of both macro and micro characteristics of red soil in karst-prone areas are significantly enhanced with the increase of intermittent time. The research results are of great significance for the prevention and control of karst ground collapse in karst areas.