EXPERIMENTAL STUDY ON THE MECHANISM OF UPLIFT FAILURE IN KARST OVERBURDEN

The change in groundwater level caused by reservoir impoundment is one of the primary factors inducing overburden failure in karst areas. Current studies on groundwater-induced overburden failure mainly focus on karst collapse,while the failure mechanism caused by groundwater uplift remains insufficiently investigated. To address this gap,a series of laboratory experiments were conducted to monitor gas pressure variations and overburden uplift displacement during groundwater level rise,with the overburden failure mechanism analyzed accordingly. The experimental results reveal the following:(1)The peak gas pressure is directly proportional to the overburden thickness when boundary conditions remain constant. In thin overburden,the peak gas pressure is relatively low,decreases gradually,and exhibits a"gradual" time-dependent curve. Conversely,in thick overburden,the peak pressure is higher and sustains for a longer duration,showing a "stepped" variation pattern. (2)The overburden deformation mode corresponds to the pressure changes. For thick overburden,"uplift" failure occurs,whereas thin overburden tends to fail in a "rupture" mode. (3)Building upon previous studies and considering the observed failure modes,a mechanical model was established to analyze the anti-destructive capacity and jacking force of the overburden. The critical thickness formulas for both failure types were derived. These formulas enable the determination of critical conditions for different failure modes under varying environmental conditions,offering both theoretical insights and practical applications.