Mechanism analysis of sinkhole formation at Maohe village, Liuzhou city, Guangxi province, China

In May 2012, a series of ground collapsing events occurred at Maohe village, Liuzhou city, Guangxi province, China during and after a heavy rainfall event. The collapsing incidents resulted in thirty-seven cover collapse sinkholes, eleven donut-shaped subsidence areas and sixty-eight earth fissures. The impact area encompasses more than 40,000 m². Extensive investigations including land use inventory, advancement of forty-nine exploratory boreholes, and geotechnical and hydrogeological analysis of soil samples were conducted to determine the contributing factors to these sinkhole formations. Because of the heterogeneity in the overburden composition and underling dolomite, the controlling factors may be different for each sinkhole. However, three factors contribute to the scale of the collapsing events: presence of cavities in the underlying bedrock, unique characteristics of overburden materials, and drastic change of groundwater levels. The wide spread cavities in the underlying dolomite make the investigation area inherently vulnerable to ground collapses. The shear strengths of the overburden materials allow for development of soil cavities in the subsurface without skylighting for a long time. The drastic groundwater level increase is the triggering factor and determines the time of the collapses. Higher groundwater levels accelerate the subsurface erosion process and enlargement of soil cavities and cause hydrofracturing and hammer effects on the soils.