Abstract: Sinkhole collapse hazards induced by karst geology have caused huge losses to Wuhan economic and social activities. Based on a combination model of sandy soil and clayey soil in overburden soil over karstic rocks, the risk hazards of the karst geological structures are divided into I, II, III and IV four categories. Many numerical analyses have been performed using the software PFC2D to investigate collapsing process of overburden soil in karst geological structures. The results indicate that the sinkhole collapsing mechanism of the all sandy soil in Class I karst geological structure belongs to sand leakage mode. The sinkhole is funnelshaped, which has a large opening at top and a small bottom. The sinkhole bottom has a loose disturbed zone deposited. The sinkhole collapsing mechanism of overburden soil consisting of upper clayey soil and lower sandy soil in Class I karst geological structure belongs to the compound failure mode of sand leakage and clayey soil bending and cracking. The upper part of sinkhole opening is a well-shaped and the lower part is a funnel shaped with loose disturbed zone at the bottom. The sinkhole collapsing mechanism of overburden soils consisting of upper sandy soil and lower clayey soil in Class II karst geological structures belongs to the failure of the lower clayey soil mode. The sinkhole collapsing mechanism of classes III and Ⅳ karst geological structures belongs to the proof collapsing in an overburden soil void mode.

Key words: Karst Geological Structure, Numerical Analysis, Sinkhole Collapsing Mechanism, Particle Flow