Abstract:

In order to rapidly analyze the influence of composite foundation and "doubletube effect" on the vertical and lateral displacements of existing doubletube metro tunnel during foundation pit excavation, the vertical and lateral additional loads of singletube tunnel under lateral resistance of pile in composite foundation is deduced to calculate the vertical and lateral displacements of singletube tunnel based on Mindlin′s solution of displacement and Winkler foundation model. The total vertical and lateral displacements of doubletube tunnels can be obtained by superposition of tunnel vertical and lateral displacements caused by "doubletube effect" calculated by iterative method, which is verified by comparison with the previous theoretical calculation results and monitoring data. Finally, the influence of the pile parameters and tunnel positions on tunnel vertical and lateral displacements caused by pile lateral resistance or "doubletube effect" is analyzed. The results show that: (1) Compared with the previous theoretical calculation results, the theoretical calculation results in this paper are more consistent with the monitored data, and the calculation efficiency is more than 28% higher than that of the original〖JP〗 twostage analysis method. (2) The influence of pile lateral resistance and "doubletube effect" on tunnel vertical and lateral displacements are not negligible. (3) Considering only the influence of foundation pit excavation on the displacement of existing doubletube tunnel, the distance between two predesigned tunnels should be reduced as far as possible, and the length of pile in composite foundation should be reasonably selected when construction conditions and rules permit. (4) The iterative method is more reasonable and accurate than onetime method, especially when calculating tunnel lateral displacement caused by lateral "doubletube effects".

Key words: composite foundation, doubletube tunnel, tunnel vertical displacement, tunnel lateral displacement, foundation pit excavation