Mechanism of karst collapse caused by punching pile construction in Jiangxia Fasi karst collapse area

In September 5th,2014,the 8-1# pile foundation construction site of Wu-Jia expressway bridge in Jiangxia Fasi collapsed and had caused large-scale ground collapse,resulting in 19 different collapse pits.Buildings were damaged and the embankment of Jinshui river also collapsed,leading to the construction rig buried and the project forced to stop for 1 year.Based on the monitoring system of Wuhan karst collapse areas,the dynamic monitoring of groundwater in multiple aquifers and monitoring of vibration points at different parts were carried out during impact hollowing in the limestone fracture zone,from which key parameters such as water level,water pressure and influence radius of fractured karst aquifer were monitored during the punching pile construction process in Jiangxia Fasi.The response of the karst aquifer water pressure to the construction process was studied,as well as the mechanisms of construction-induced overburden collapses were researched.The study shows that the Quaternary confined aquifer is deeply influenced by inner construction activities,but the variation of the water level is relatively flat.In the fractured karst acquirers which are very heterogeneous,when the karst channels are not exposed on the surface,the construction has little effect on the karst water.However,if they are exposed,the karst water level may have a sudden in crease which will increase the risk of karst collapse.