Experiment Study of the Failure Mechanism and Evolution Characteristics of Water–Sand Inrush Geo-Hazards

Abstract

Water–sand inrush disasters are frequently encountered during underground engineering construction in karst terrain. The objective of this paper is to study the failure mechanism and evolution characteristics of water–sand inrush caused by the instability of filling medium in karst cavity, as well as the impacts of soil compactness, hydraulic pressure and confining pressure on the instability process. In response to this purpose, a stress-controlled seepage test apparatus in consideration of particle loss was designed, and a series of seepage tests were performed correspondingly. The test results indicate that: (1) Based on the nonlinear feature analysis of water-outflow pattern, the water–sand inrush process can be divided into the “slow flow” stage, “transition flow” stage and “pipe flow” stage by Transition Point I, II. (2) The decreasing soil compactness and increasing hydraulic pressure both exponentially facilitate the seepage-erosion process by increasing the particle-erosion ability; the increasing confining pressure extends the “slow flow” stage and shortens the duration of the “transition flow” stage, ultimately advancing the occurrence of the “pipe flow” stage; the existence of critical hydraulic pressure for the seepage-erosion progress is confirmed, the occurrence of the “pipe flow” stage is significantly advanced once the hydraulic pressure over the critical value. (3) The particle loss caused by the seepage-erosion process is the internal mechanism of water–sand inrush, the variation characteristics of water-outflow pattern are crucial external manifestations correspondingly. Therefore, with the monitoring of water-outflow pattern variation tendency as indicators, the critical status of water–sand inrush can be near-real-time identified, which offers experimental foundation for the early warning and forecast of the occurrence of water–sand inrush.