Double-exponential variation law of water-inflow from roof aquifer in goaf of working face with mining process

The roof aquifer will be destroyed by the extraction of coal working face,and affects the mining safety con- versely. Based on the system dynamics theory,the authors proposed a double-exponential decay model to describe the water-inflow process of roof aquifer with the working face extraction. The authors tested the hypothesis that the process would exhibit spatial variation using typical coal faces with different mining rates in Yuanyanghu mine area,Ningdong coal field. As mining duration increased,the water-inflow process increased trend initially,until reached a peak value,and finally decreased to a equilibrium value with the certain advancing lengths of the coal faces. The approximate solu- tion of model parameters with physical meaning was determined by McLaughlin formula,as well as the water-inflow with peak value and equilibrium value,and their occurring location. The results indicated that the characteristics of wa- ter-inflow process were controlled by the dynamic and static inflows,and the dynamic recharge was the main control- ling factor. When the condition that the roof aquifer was similar and the tectonic influence was negligible,the mining rate determined the occurring location of the water-inflow with peak value and equilibrium value,while the peak value and equilibrium value were affected by the mining thickness,lithologic characteristics of the roof and the characteris- tics of the aquifer. The conclusion provides a new way for predicting the water-inflow of working face with reasonable trend and high precision.