Development features and formation mechanisms of karst collapses in the Tailai basin, Shandong Province

The Tailai basin is located in the east of Shandong Province. By the end of 2013, the history records karst collapses up to 161 in number, which occurred at 97 locations. Based on previous studies, the updated survey and monitoring results, this work makes a research on karst styles, characters and formation mechanism of karst collapses of the Tailai basin. The results show that these karst collapses are concentrated in the groundwater drawdown funnels and affected areas. Their distribution is obviously controlled by geological structures. The thickness of Quaternary System above the subsidence areas is generally less than 30 meters, with underlying bedrock of Ordovician limeston. More than 80% of the karst collapses occur in flood seasons. Three geological models of karst collapses are established on the basis of stratum structures and groundwater dynamic conditions at collapse sites: (1) karst collapse in single-layer structure without aquifer; (2) karst collapse in two-layer structure; (3) karst collapse in multiple-layer structure with aquifers. The process of the first karst collapse is “vacuum suction erosion-disintegrating peel-collapse”. The process of the second karst collapse is “seepage deformation-disintegration-collapse” or “vacuum suction erosion-seepage deformation-collapse”. And the process of the last one is “vacuum suction erosion-seepage deformation-disintegration-collapse”. This paper provides scientific basis for risk prediction and geologic hazard control in karst collapse areas.