Karst ground collapse, a geological disaster in karst areas characterized by the sudden subsidence of surface rock and soil, poses significant risks to human life and property owing to its abrupt and frequent occurrence. Karst ground collapses can be classified into soil-cave-type and hourglass-type, based on the viscosity of the overlying layer. Among these, the hourglass-type presents a higher collapse risk owing to the lack of cohesive forces in the overlying layer. This study focused on hourglass-type karst ground collapse, utilizing physical model tests and the discrete element numerical simulations to develop and validate a collapse model. The physical model tests reproduced the collapse process and provided insights into its underlying mechanism. Numerical simulations were employed to evaluate the effects of karst channel conditions and drilling-induced vibrations on hourglass-type collapses. The results indicated that although the length of the karst channel had minimal impact on collapse speed and pattern, a wider karst channel resulted in a faster collapse and a larger final collapse pit. Moreover, vibration loads increased the collapse speed, shifted the collapse pit towards the vibration source, and expanded the scale of the collapse, thereby amplifying the overall damage extent.

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.