Abstract:

The pipe length is a key parameter to the design and construction of Gongbei Tunnel curved pipe roofing. In order to optimize the pipe length, the pipe static equilibrium conditions under the effect of jacking force and earth counterforce is analyzed; the distribution models of earth counterforce in conventional and unit curving pipe jacking methods are obtained. The pipes located in the top, middle and bottom of the pipe roofing as well as mucky soil are selected as study objects so as to analyze the influencing rules of pipe length and soil parameters on earth counterforce. The results show that: 1) The maximum earth counterforce exists in the first pipe of conventional pipe jacking and it diminishes with pipe length increase. 2) On the contrary, the earth counterforce in the first pipe of unit curving method is the smallest and it increases with pipe length increase. The preliminary analysis determines the pipe length of 4-5 m. Considering the reduction of overbreak, the convenience of rectification and the size of working shaft, the project has successfully completed by employing 4 m long pipe with conventional pipe jacking method.

Key words: Gongbei Tunnel, curved pipe roofing, pipe length, jacking force, earth counterforce