COMPARATIVE STUDY ON ADAPTABILITY ANALYSIS OF THREE BENCHING SEVEN STEPS AND TEMPORARY INVERT METHOD FOR LARGE-SECTION TUNNEL IN SOFT STRATUM

Soft rock has poor mechanical properties, low strength and stability. At present, three benching seven steps commonly used in the construction of a soft rock tunnel have the characteristics of large initial support deformation, large surface subsidence, difficulty in timely closure, and low strain capacity to emergencies, etc. In view of the specific conditions of weak surrounding rock at the entrance of two high-speed railway tunnels in Chizhu and Gaodong of Guangdong province, the comparative tests of three-step seven-step method and three-step temporary inverted arch method are carried out. Based on the tests of tunnel vault settlement, peripheral convergence and surface settlement, a systematic study on the adaptability of construction method is carried out from the aspects of engineering application effect and numerical simulation. The results show that: the three-step temporary invert method is superior to three-benching seven-steps in controlling arch settlement, surface settlement, surrounding rock stress, plastic zone expansion area and depth in large-section tunnel construction of this kind of soft rock stratum. The conclusions can be used for reference to other similar projects.