UNDERLYING TUNNEL DEFORMATION CAUSED BY EXCAVATION AND DEWATERING OF FOUNDATION PIT BASED ON KERR FOUNDATION MODEL

The excavation and dewatering of foundation pit inevitably disturb the stress fields of the surrounding soil layers, which threatens the operation of underlying tunnels. A two-stage analysis method is adopted to propose the analytical solution to the longitudinal deformation of the underlying tunnel caused by the combined effects of foundation pit excavation and dewatering. At the first stage, the Mindlin elastic solution and effective stress principle are used to determine the additional stress caused by excavation and dewatering. Then the longitudinal deformation is obtained by assuming the shield tunnel as an Euler-Bernoulli beam resting on a Kerr foundation. The proposed model is verified by comparing the theoretical predictions with the monitoring data from practical engineering cases. Also the results obtained by ignoring the influence of dewatering and the Winkler model are employed for the further comparison. The influences of excavation length and width, the diameter and buried depth of the tunnel, water level drop depth and the relative position of the tunnel to the pit on deformation are analyzed. The results show that the proposed model, incorporating the impact of dewatering, can predict the tunnel deformation more precisely. With the distance between the tunnel axis and the center of the foundation pit increasing, the tunnel deformation decreases.