Deformation and failure of overburden soil subjected to normal fault dislocation and its impact on tunnel

Abstract

In this study, a large-scaled model test was conducted to explore the deformation and failure mechanism of tunnel with fault rupture. The strain evolution, ground fissure and displacement, earth pressure and tunnel deformation are collected in the test. Then, tunnel mechanical behavior under the fault dislocation is revealed based on the test result. The results show that a prismoid-like 3D shear zone appeared within fault fracture zone. The tunnel experiences an elongated ‘S’-shaped deformation along longitudinal axis of tunnel and the displacement changes of sectional linings within the shear zone are more significant. In transversely, the linings exhibit an oval horse-shoe deformation pattern. Three types of failure mode defined as Type Ⅰ, Type Ⅱ and Type III, corresponding to slight damage, moderate damage and severe damage, are summarized transversely in this paper. Under normal fault dislocation, the tunnel within the shear zone experienced a combination failure of bending moment and shear force. But compression failure of linings far from the fault would occur with longitudinal cracks on tunnel subjected to normal fault. Taking fault width (Wf) and tunnel span (St) into consideration, a reasonable tunnel fortification length was proposed with maximum of 2.25Wf and 3.5St under a specific fault dip of 60°. In the model test, when the fault dislocation reaches 10 mm, a slight crack begins to appear on arch foot of lining and then dislocation of joint occurs. Thus, corresponding to a prototype tunnel, a safe vertical displacement to ensure no damage to tunnel should be 34.6 cm when a segmentally designed tunnel is subjected to normal fault dislocation.