关键词: 软土盾构隧道, 地下水位升降, 非均匀收敛变形, 地表沉降, 衬砌响应, 复变函数理论

Abstract: A high risk will be raised when the groundwater level changes dramatically during the construction of shield tunnel. However, the impact of fluctuation of groundwater table is seldom considered in the construction of shield excavation in current studies. Besides, the deformation and stress analysis of tunnel lining are paid even less attention. The non-uniform convergence deformation at the periphery of the tunnel cavity is introduced into this paper, considering the fluctuation of groundwater level when the shield tunnel is being constructed. The complex functions are applied in calculating the deformation of ground and lining and stress caused by shield tunnel excavation under the influence of the variation in groundwater table. The presented method is proved to be reliable by comparing the theoretical analysis results with the numerical simulation results. In addition, sensitivity analysis of parameters such as the groundwater level depth, thickness of lining, radius of tunnel is carried out. The results show that the radial displacement of the lining presents a stem-upwards "apple" shape. When the groundwater level decreases, the radial displacement gradually transforms from "duck egg" shape to "apple" shape that tends to be more and more obvious. The circumferential displacement of the lining likes an inclined "apple". With a decline of groundwater level, the range of the oblique "apple" expands. Under the influence of lining thickness, tunnel radius etc., the distribution of radial stress shows the same variation rules as mentioned above. With the increase in these two parameters, the distribution of radial stress gradually changes from the horizontal “duck egg” to “ ” shape. As the groundwater level drops, the shape of radial stress shrinks towards the center. The circumferential stress of the lining decreases slightly with an increase in thickness of the lining. While it decreases obviously with an increase in the tunnel radius. As the groundwater level drops, the distribution of circumferential stress gradually changes from the vertically placed "duck egg" shape to the "8" shape. The tangential stress of the lining shows the same variation rules under the influence of lining thickness and the tunnel radius. The distribution of tangential stress shows a stem-downwards "apple" shape. The research results can give a reference to the shield construction when the groundwater level changes obviously.

Key words: shield tunnel in soft clays, groundwater levels rise and fall, non-uniform convergence deformation, surface settlement, lining response, complex function theory