Abstract:  Pregrouting technology is often adopted to rapidly seal the water leakage of the working face of the deep and large vertical shaft constructions of a railway. In this paper, a case study is conducted on the shaft No. 1′s water seal of the Gaoligongshan tunnel on DaliRuili railway in weathered granite formation using working face pregrouting. A targeted working face pregrouting scheme of exploration + grouting is determined according to the geological conditions revealed through inspection holes and excavation results. Based on field tests, the influences of the pregrouting scheme, drilling efficiency, and drilling hole depth on grouting effect and efficiency are analyzed; in conclusion, the optimal depth of the shaft No. 1′s drilling hole of the Gaoligongshan tunnel is 60 m. A rational drill hole depth can help in improving comprehensive construction progress by 6.3%~15.8%, guarantee the water seal effect of working face pregrouting, improve comprehensive construction efficiency, and save construction cost.

Key words: railway tunnel, deep and large shaft, working face pregrouting, circulating drilling hole depth, construction efficiency