Study on Technology of Surface Pre-grouting for Vertical Shaft in Broken and Water-rich Granite Strata of Gaoligong Mountain Tunnel of Dali-Ruili Railway

Abstract

The Gaoligong Mountain Tunnel of Dali-Ruili Railway is located between the Nujiang River and the Longling County Town in the southeastern section of the Hengduan Mountains, China. In geological history, this area was affected by multiple tectonic movements, and the faulted structures are extremely developed. During the drilling inspection hole of No.2 vertical shaft, boring tool stuck and the hole collapse once happened. Its depth was 643.12 m, the outcropped strata were all granite or weathered granite (fracture zones). 7 fracture zones with thickness > 10 m were uncovered, the maximum thickness of which was 112.95 m; and 7 water bearing strata were uncovered, of which the buried depth of groundwater table was all less than 34m, the permeability coefficients(k) were 0.005∼0.158 m/d. It was estimated that the water inflow of ④ ∼ ⑦ aquifers of the main shaft and the auxiliary shaft of No. 2 shaft were all greater than 120 m3/d (5 m3/h), that normal water inflow of main shaft and auxiliary shaft of No.2 vertical shaft would be 125.92 m3/h and 90.08 m3/h respectively. In order to avoid water inrush and wall caving accidents during the construction of the two shafts, it was decided to adopt the surface pre-grouting method in the construction of the shafts to block off and reinforce the ④ aquifer and the strata under the aquifer. The “S” shaped directional drilling technology was used; the two sequences, segmented downward, multiple-times grouting mode was adopted; clay-cement slurry was selected as the grouting material. After grouting, pump yield water tests were carried out in two grouting holes of main shaft and auxiliary shaft. The remaining water inflow in grouting sections of two shafts was 5.02 m3/h and 5.70 m3/h respectively, and the rates of water blocking were all over 93%. The grouting effect was remarkable. The successful implementation of the surface pre-grouting project of No.2 vertical shaft in Gaoligong Mountain Tunnel of Dali-Ruili Railway has important guiding significance for the design and construction of tunnel and mine shafts in broken water-rich granite stratum.