| Most of southwest region mainly in the mountains, in order to solve the contradiction of land, people usually use "the mountains fill valley" method to solve the construction problem, Thus creating a lot of backfill. The rapid development of subway, a lot of subway tunnel have to cross the backfill area. The backfill formation age is generally close. It has complex composition and loose structure, so its mechanical properties is very poor, the construction of subway in backfill section easily cause the tunnel collapse, water inflow and security issues. Moreover, in the operational phase of the subway, the vibration effect is more prominent, and there are a lot of security risks. This paper has mainly studied the the backfill tunnel’s dynamic response by combining theoretical analysis and numerical simulation method which is based on backfill project of the 5th and 10 th of Chongqing subway line. First of all, this paper studied the dynamic response of the backfill tunnel structure which under dynamic loads and its influencing factors. Then the paper studied the sheet pile foundation’s seismic effects of the tunnel which located in backfill area. Finally the paper predicted the cumulative settlement of the tunnel which located in backfill area in operational phase of the subway by using a simplified calculation model of soft soil under cyclic loads. The main work and research results are as follows:(1) Obtained the engineering characteristics of backfill which including density, moisture content, particle size distribution and mechanical parameters by the method of experimental research. Analyzed the dynamic deformation parameters of backfill with backfill’s shear wave velocity(2) By using the transient analysis of ANSYS finite element software, the vertical displacement, velocity and acceleration response of backfill tunnel in dynamic case is studied. Through analysis, the backfill tunnel’s displacement and velocity response gradually decreases by the distance from the vibration source increasing. Vertical acceleration response is gradually reduced as a whole by the distance from the vibration source increasing, but the acceleration response of the backfill surrounding the liner significantly higher than the lining. The dynamic response in the horizontal direction decay faster than the vertical direction.(3) The paper selects the ground surface, the vault, the left wall, right side wall and the track surface center of the left tunnel as monitoring sites. Studying the factors that affect backfill tunnel’s response under dynamic loads, including tunnel depth, span, lining elastic modulus, elastic modulus of backfill and traffic condition.(4) The paper make a studying of the Pile-Plank foundation’s effect on the dynamic response of the structure of the backfill tunnel from the aspects of the number of lateral pile, pile length, lateral spacing pile and the diameter of the pile.(5) Studied the cumulative settlement of the soil below the lining under the conditions that when the tunnel has no pile foundation and when the tunnel has pile foundation. For the paper studying by two-dimensional model which can not consider the impact of the load along the track direction of the tunnel, the paper conducted a gradual reduction of the wheel-rail forces in order to fully consider the rail’s dispersion for the train loads and the buffer of the damping layer. |
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