Abstract：Abstract：Yuanliangshan tunnel，with a total length of 11.068 km，is the longest tunnel on Chongqing—Huaihua railway. The tunnel goes mainly through the core of Maoba syncline core，Tongmaling anticline and Lengshuihe shallow-buried section，where the Maoba syncline，Tongmaling anticline and ruptured zones develop. Because of the influences on the geological structures，there exist two layers of artesian water of P2w+c and P1q+m. The deep-hole drilling exploration shows that the pressure of the artesian water reaches up to 4.42–4.60 MPa. On the basis of the exploration data and the surrounding environment，it is estimated that the normal water inflow of the complete tunnel reaches 98 000 m3/d with the maximum water inflow of 145 000 m3/d. During the construction of Yuanliangshan tunnel，5 karst caves have been encountered in Tongmaling anticline and Maoba syncline，which have different shapes and different filling materials such as fine silty sand，silty clay and clay. Among them，the karst cave No.2 is the most difficult for it is filled silty fine sand layers. Due to the influence of the high pressure，rich water and karst geology，several large-scaled sudden water inflows，sand inflows and mud inflows are encountered，which have imposed serious influences on the safe and successful constructions of the tunnel. By means of silty fine sand layers，the paper researches the grouting systems that consists of cement single liquid grouting material，MC super and thin cement single liquid grouting materials，cement and water glass of liquid grouting materials，MC super and thin cement and water glass of liquid grouting materials，TGRM single liquid grouting material，and HSC single liquid grouting material，respectively. The grouting design，grouting parameter，grouting result check of the karst cave No.2 and two passive countermarch returns to fill the situation are analyzed，which can provide an important reference for future tunnels under similar geological conditions.
