The Application of Soil Nail in Mila Mountain Tunnel

Mila Mountain Tunnel is located in Tibet, China. It is about 5.7 kilometers long and 21.5 meters wide. It belongs to the first-class highway with bi-directional and four-lanes. Speed is predicted 80 kilometers per hour. The pavement of whole line is bituminous concrete. And this project plans to be opened to traffic in September, 2017.

It is introduced that Mila Mountain Tunnel is the highest highway tunnel in the world, air is thin, pressure is low, national and geological conditions are harsh. The left hole, right hole and inclined shaft of this tunnel are IV.V-class surrounding rock, and it has several technological problems of rock deformation, mud outburst, water gushing and ventilation, etc. The process is complex and difficulty is quite great, so it has high request on construction quality.

Facing with so many difficulties and challenges, supporting operation of soil nail has played an important role on the safety of construction.

There are several problems need to be considered during the construction:

1. Before installing soil nail, there are loose rocks falling down when cleaning. So workers shouldn’t operate under this area.

2.When working on muck bank or frame, safety should be noticed.

3.Workers should operate with each other. Temporary supporting shouldn’t be canceled before linking steel frame and soil nail.

4.When deformation or crack appearing during the process of drilling and grouting, efficient remedial measures should be adopted according to conditions and workers should leave danger areas immediately.

5.When mortar grouting into soil nail, pressure gauge should be checked closely. If the indication is too high, special measures should be adopted and ignoring blocking. In addition, nozzle of grouting pipe should not point to people.

6.Workers should operate according to the operation procedure strictly, ignoring the occurrence of security accident.