Study on the construction mechanical response of the double-shield TBMs of a long diversion tunnel crossing a fault fracture zone

Abstract

The Bheri Babai Diversion Multipurpose Project (BBDMP) in Nepal is located in the southern foothills of the Himalayas. The tunnel of this project passes through the Siwalik rock stratum. In this paper, the mechanical numerical model of the double-shield tunnel boring machine (TBM) crossing the fault fracture zone is established based on the morphology of the developed joint in the Bheri fault zone of the BBDMP. By analyzing the influence of joint group on double-shield TBM tunneling, the variation rules of the surrounding rock displacement, plastic zone distribution, and internal force of TBM crossing the fault fracture zone are obtained. The results of the research demonstrate the following: (1) when the single-shield tunneling mode is used in the fault fracture zone, the surrounding rock displacement is larger than that in intact rock mass, and the dissymmetry of joint geometry leads to the dissymmetry of the displacement distribution. (2) The plastic zone of the surrounding rock is mainly distributed along the geometric plane of two joints. The maximum value appears in the area from the left arch waist to the left arch shoulder and from the right arch waist to the right foot of the wall. The joints at all the other sites reach the yield state, except for the area around the vault and inverted arch, with a range of about 0.3 times the tunnel diameter. (3) The existence of joint surface leads to the asymmetrical distribution of the internal force in the pipe segment. The minimum safety coefficient appears at the left shoulder and right foot of the wall.