Delay characteristics and risk mitigation of karst water burst flood of tunnels

Based on field tests on 19 groups of data and phenomenon analysis of inrush or bursting waste from karst cavity of Maluqing tunnel of Yichang-Wanxian Railway, a conceptual model of karst water burst flood (KWBF) is proposed by means of statistical analysis and phenomenological induction. Through analyzing its characteristics during different construction stages, it is shown that KWBF has the delay characteristics. The time history analysis of the karst water burst flood shows that because of pressure dispersion between inside and outside of the cavity, seepage enlargement is evolved into conflux so as to deprive groundwater from aquifer aqueduct and fracture, and the water together with mud suddenly releases from karst into the tunnel. The key factor for the delay characteristic of KWBF is water amount and silt or filling degree of conflux aqueduct. The delay time of KWBF on supply air continuously reduces the response time, according to which the possibility of KWBF is reduced. Forecasting of KWBF is conducted by use of the rainfall seeping theory and statistical analysis method. The basic data are obtained from field quantity observation such as rainfall and hydrograph measurement. The control index of safe operation during the rescue and discharge period is proposed.