Abstract：The geologic condition of the high-pressure and water-rich area in Maoba syncline at Yuanliangshan tunnel of Chongqing—Huaihua Railway is complex and regarded as a for bitten area of tunnel construction. The karst development characteristics of this area is systematically introduced；and the geologic and karst structure is classified. The distribution and shape of karst caves and the filling in them are investigated by the advanced investigation means，and reliable forecast is made accordingly. Based on analysis of structure and intensity of the filling，the reasonable grouting materials and grouting technology are determined. Pre-grouting，radial grouting in surrounding rock and reinforcing grouting behind lining are implemented respectively according to the geologic condition；and inspecting method and estimating method of grouting effect are also brought forward to ensure the grouting reliability. Satisfying results are achieved；and safety of tunnel construction is ensured through adopting these measures. The results can provide references to tunnel construction in karst region.
