Study On Water Inflow Prediction In Wulingshan Tunnel Of Qiangzhangchang Railway

Due to the high in-situ stress and water content of highly developed karst zone,water inrush accidents often occur in extra-long and deep-lying tunnels.The prediction of water inflow is of utmost importance to ensure the safety of tunnel construction.However,the extremely complicated geological conditions and the limitations of existing prediction methods,which has produced large deviations in the prediction results of water inflow.Based on the research status of water inflow prediction of karst tunnel,this study predicted the water inflow rate of Wulingshan tunnel during construction period and operation period Main research results are as follows:(1)Seven types of karst tunnel water inflow modes were summarized through data investigation and analyses of water inrush characteristics.According to the geological conditions of the study area and the water inrush records,the water inrush mode of the Wulingshan tunnel is judged as the rapid flow type of dynamic reserve with high precipitation recharge and lag flow type of dynamic reserve with high precipitation recharge.(2)Based on hydrogeological conditions,karst development of research area and tunnel's location.Conceptual model of water inflow in Wulingshan Tunnel was been established.water inflow predictions of tunnel sections were carried out by using analytical formula,and the most applicable formulas for the prediction of maximum water inflow rate and normal water inflow rate in each section were analyzed and determined.(3)Based on the karst duality theory,hydrogeological conceptual model of research area was established.The continuous coupling pipe-flow model was established by using MODFLOW-CFP to simulate the regional groundwater seepage field,then the parameter sensitivity of the model was analyzed.Finally,the model was calibrated.(4)Meanwhile,dynamic excavation scenario and permeability change of surrounding rock was conducted.To verify its feasibility,the model was applied to Wulingshan tunnel in China and calculated numerically.The prediction results of the two sections of tunnel were generally in a good agreement with the field-observed results,the errors were 13.3% and 5.4% respectively,MODFLOW-CFP performed better than MODFLOW.(5)Water inflow prediction results of operation period indicated that,normally,water inflow of the tunnel is smaller in the dry season,the water inflow increases with the rise of precipitation recharge in flooding season.For the safety of transportation,the monitoring of rainfall and lining water pressure should be strengthened during the operation period.Results of this study indicated that MODFLOW-CFP can well achieved the duality of karst aqueous medium.It has higher prediction accuracy than existing methods and reflect the dynamic variation characteristics of tunnel water inflow.It has theoretical value and guiding significance for karst tunnel water inflow prediction.