The seepage pressure effects are comprehensive actions on cover-layer in the process of rain feeding karst groundwater

which includes load-increased effect of water

vertical-seepage effect

wetting-soft effect and obturation negative-pressure effect. And the seepage pressure mechanism is the primary mechanism of karst collapse in the center of cone of depression in continual pumping region. Based on the theory of М•М•Протодьяконов

the limit equilibrium theory and the karst collapse law in Zaozhuang city

this paper has established the mechanical model of surface-collapse phase and determined the height of equilibrium soil-hole in inter-collapse phase. Meanwhile

an evaluation of karst collapses in Zaozhuang city has been carried out by means of the formula and mechanical model. The result shows that the formula and mechanical model coincide with the forming mechanism of karst collapse in Zaozhuang city.