Abstract
Tunnel portal sections always suffer serious damage under strong earthquakes. This paper aims to study the seismic performance of lining strengthening method in soft rock portal section by employing the model test. Firstly, the shaking table test considering the test cases, the modified input motions, the boundary condition, and monitoring equipment are conducted to simulate the seismic response of the soft tunnel portal section. Then, the lining strengthening method of increasing concrete grade is applied to the tunnel structure to study the aseismic performance of the soft rock tunnel portal section, and the seismic effects of the tunnel linings with different concrete grades are compared and analyzed. The result shows that the proportion of soft rock to total surrounding rock is the key factor affecting the seismic response of soft rock tunnel portal section; the larger the proportion of soft rock in surrounding rock, the more vulnerable the structure to earthquake damage; the seismic performance of the lining strengthening in hard rock portal is remarkable while limited in soft rock portal section. The stiffness and strength of the lining are larger than those of surrounding rock; the seismic performance of the soft portal section could hardly be improved only by the lining strengthening method. It is suggested to adopt both the structure strengthening and isolation method in the seismic design of soft portal section.
Highlights
Underground structures were believed to suffer less damage during the strong earthquake since they were surrounded by rock or soil [1, 2]
In view of the serious earthquake damage of soft tunnel portal section, the seismic performance of lining strengthening method for tunnel structure is studied by conducting the large-scale model test
The shaking table test considering the test cases, the modified input motions, the boundary condition, and monitoring equipment are established to simulate the seismic response of the soft tunnel portal section. en, the lining strengthening method of increasing concrete grade is applied to the tunnel structure to study the aseismic performance of the tunnel portal at the junction of soft and hard rock, and the seismic effects of the tunnel with different concrete grades are compared and analyzed
Summary
Underground structures were believed to suffer less damage during the strong earthquake since they were surrounded by rock or soil [1, 2]. Due to the construction difficulty and the high construction cost, the damping layer is only used in the test section of the tunnel and has not been widely used in the tunnel seismic design Another isolation method is that the damping joint with the simple construction technology can achieve almost the same effect of shock absorption, while the existence of the joint may reduce the waterproof performance of tunnel so as to shorten service life of the tunnel [15]. There are few shaking table tests on seismic response and structure strengthening of tunnel portal section, especially in soft soil. Afterwards, the structure strengthening method by increasing concrete grade is employed in test to investigate the its seismic effect. Is study is of great significance to improve the seismic performance of tunnel soft rock portal section Scientific suggestions are put forward for seismic design of portal section in soft rock. is study is of great significance to improve the seismic performance of tunnel soft rock portal section
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