Abstract: To rationally determine the support timing of deepburied tunnels with high ground stress, improve the support structure quality, and reduce the support cost, a case study is conducted on a deepburied plateau tunnel with high ground stress. Safety factor, displacement increment, and plastic zone methods are employed to determine the reasonable support timing of the support structure, and the applicability of each method is analyzed and compared. The results reveal the following. (1) The distribution laws of cave wall yield calculated by the three methods agree, it is easier to yield at the crown and invert than at the waist and foot. (2) The results of support timings by the various methods differ; under the same buried depth, the safety distance obtained by the safety factor method is greater than that obtained by the plastic zone and displacement increment methods. The engineering analogy shows that the plastic zone and displacement increment methods are more conservative than the safety factor method; thus, the safety factor method is recommended when determining the support timing.

Key words: deepburied tunnel with high ground stress, support timing, safety factor method, displacement increment method, plastic zone method