DEEP IMMERSED TUNNEL SUBJECTED TOMAJOR FAULT RUPTURE DEFORMATION

Immersed tunnels are particularly sensitive to tensile deformations such as those imposed by an outbreaking normal earthquake fault.The paper investigates the response of a proposed 70 m deep immersed tunnel to the action of a major normal fault rupture occurring in the basement rock underneath the tunnel. Non-linear finite elements are used to model the quasi-static fault rupture propagation through the soil overlying the bedrock and the ensuing interaction of the rupture with the immersed tunnel. The tunnel is modeled as a 3-D flexural beam connected to the soil through properly-calibrated non-linear interaction springs, the supports of which are subjected to the free-field fault-induced displacement. The joints between the tunnel segments are modeled with special nonlinear hyper-elastic elements, while their longitudinal pre-stressing due to the 7-bar water pressure is also rigorously incorporated in the analysis. The possibility of sliding is considered through the use of special gap elements. The influence of segment length and joint properties is explored parametrically. The analysis shows that a properly designed immersed tunnel (suitable thick elastic gaskets, smalllength of segments, shear keys with sufficient allowance , un-stressed tendons) can safely resist anormal earthquake fault rupture with a dislocation of 2 meters in the basement rock, 800 m underneaththe tunnel. Net tension or excessive compression between the tunnel segments can be avoided withsuitable design of the joints.

کلیدواژه ها:

Immersed tunnel ، fault rupture propagation ، soil–structure interaction