Spatial-temporal distribution and causes of karst collapse in the Xuzhou area

Xuzhou is the only city in the Jiangsu Province to use the karst underground water as the municipal water. Due to the long-term absurd use of the Karst underground water, karst collapse often happens in the Xuzhou region. This paper looks into the distribution of bare karst and covered karst in the Xuzhou region in northern Jiangsu Province and the special and temporal distribution of karst collapse in the history, and summarizes rules of the karst collapse. Firstly, as controlled by the fault zone of the ancient Yellow River, the Karst developed more intensive when closer to the ancient Yellow River and vice versa. Secondly, the collapse occurs in sections with shallow well developed karst, mostly in Ordovician limestone and a few in the Cambrian limestone. Thirdly, the collapse is concentrated within the ancient channel. Most collapse happens in the sand soil monolayer, some in the clay sand-clay layer. Lastly, all collapse is in the cone of depression due to the extraction of karst water. In combination with the correlation between the timing of karst collapse and the dynamics of ground water, this paper comprehensively analyzes the causes of ground collapse. Though the overlap section of the ancient watercourse and the fault zone of the ancient Yellow River provides favorable condition for the karst underground collapse, its final occurrence is resulted from human engineering activities, which change the karst water level significantly and causes rapid decline in volatility. The results of this study would provide scientific basis for prevention of karst collapse hazards in the Xuzhou city in the future.