River Bay Tunnel is one of the key projects for the special highway transportation of Xiluodu Hydropower Station on the Jinsha River. The length of the whole tunnel is 3,116m. The rock condition is loosely stacked stones, sub clay and gravel layer and mixed with water.
In the construction process of the River Bay Tunnel exit , the first is to design the big pipe-shed according to the drawing, using the DTH Drill with superior performance, high efficiency, and large drilling capacity and with an eccentric drill bit. But in the actual operation, the maximum drilling depth is less than 3m. The main factor is sticking, resulting in deviating from the design direction in the construction. Big pipe-shed advanced support scheme was thus stranded. After the analysis of above reasons, considering the features of self drilling rock anchor, the contractor decided to use the 4m R25N rock anchor for short pipe-shed advanced construction. Self drilling rock anchor has the following advantages for advanced support:
(1) Self drilling rock anchor and drill rod can be merged into one, with a small diameter drill bit and without eccentric block. It’s easy to drill;
(2) Drilling the hole directly, no need to be pulled out and no collapse and blockage phenomenon;
(3) The anchor bar is hollow, which can be effectively grouting and bear large load, ensuring the grouting diffusion radius and the anchoring effect of surrounding rocks;
(4) The pipe-shed is short and easy to install, easy to operate, and can work at multi-points simultaneously.