Dynamic Behavior of Portal Part of Traffic Tunnel in High-Intensity Earthquake Area

A large-scale shaking table test is accomplished on the dynamic response and failure modes of the tunnel. The result is that the largest dynamic response of tunnel structure appears at the side-wall and the shear or fracturing damage appears at the invert, which is basically the same damage state with tunnel engineering in 5.12 Wen Chuan earthquake. The internal force value of tunnel structure minish and the numbers of cracks reduce after the shock absorption layer is set up in model test, and optimize the stress state of tunnel. The surface cracks of tunnel model appear firstly at both spandrels and develop diagonally at the tunnel entrance. The cracks arise "X"-shape distribution on the surface of the model soil. There are a lot of circumferential cracks at tunnel portal under the condition of dynamic loads, and most of longitudinal cracks or oblique cracks can terminate when extending to the circumferential cracks. So that it is proposed that there should be designed more shock absorption seams in the vicinity of tunnel portal in order to be propitious to damping the earthquake energy.