Application of Self-drilling Anchor Bolts in Vertical Shaft at Left Bank of Xiluodu Hydropower Station

Self drilling anchor bolt has two performances: drilling and grouting. It features a hollow bore for flushing, or simultaneous drilling and grouting. It can be installed in sites with weak rocks, loose soil, weathered layer, sand with stone layer where it is so difficult to create a hole in complex formation. The unconsolidated ground conditions favor the self drilling anchor bolt technique for fast and simple method of installed compared to the traditional method, which was confirmed by the application in Vertical Shaft at Left Bank of Xiluodu Hydropower Station.

The engineering geological conditions at the left bank is very complicated and the construction period is short, which means the overall is so dangerous that it demands for adjusting the conventional supporting method to be adapted to the project. There are three geological stratification from the top to the bottom. First, diluvial deposit (plQ3). Its structure is
inhomogeneous to bring about collapse of the shaft easily. Second, glacier deposit (fgl+glQ2), which has bad autostability. Third, ancient landslide deposit, which is composed of triassic system amaranth sandstone and the macadam of limestone.

This project includes NO.1 and NO.2 outlet shaft, and both are 251m deep. According to the surrounding rock situation, the shaft divides covering stratification and stone stratification. The covering stratification of NO.1 shaft is 115m deep and NO.2 126m deep. The diameter of covering stratification excavation ranges from14.0~14.6m, and the diameter of stone stratification is 11.50m. The surrounding rock in the covering stratification is relatively weak so it needs supported when dug 3.0~4.5m deep. The length of the self drilling anchor bolt is 6m. The depth of drilling is 5.5m and the interval space is 1.2m*1.0m. Finally, C40 concrete should be applied for lining construction of long inclined shaft, and the thickness is 1.2m.

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