Discussion on lining strength of railway tunnels in karst areas under instantaneous heavy rainfall: An example of the Yuanbaoshan tunnel of Zhijin-Bijie railway in Guizhou Province

Guizhou is a karst highly developed province, where heavy rainfall often destroys tunnel lining. A typical case is that on the eve of opening of the Yuanbaoshan tunnel of the Zhijin-Bijie railway in Guizhou, an instantaneous heavy rain caused many damages of second-time linings at many places in the tunnel, such as extrusion, collapse, spalling, cracking, water inrush, and dripping, resulting in the cancellation of the railway opening planned. This work attempts to analyze the mechanism of this hazard. In terms of MIDAG GTS numerical simulation software, we calculate the displacement, axial force, bending moment and shear stress of the second-time linings under normal conditions and 50 m water pressure on linings, respectively, and examine the effect of instantaneous heavy rainfall on the strength of lining. Results show that， (1) without considering the water pressure, the second lining structure is relatively safe. When the instantaneous increase of 50m water pressure is posed, the lining structure is not safe because of the excessive internal force. (2) For the karst sections with groundwater development, if there is no specific data of water pressure, it is recommended that in the third-grade surrounding rock section, reinforced concrete lining is used to increase the lining’s resistance to local instantaneous water pressure rising. (3) Discharge and decompression are the key measures to solve the problem that the lining is destroyed because of the excessive water pressure.