Abstract: To investigate the behavior of surface settlement caused by Sshaped spatially curved pipe jacking for tunnel constructions, a calculation method is proposed to obtain the surface settlement caused by Sshaped spatially curved pipe jacking, based on Mindlin′s elastic solution and the random medium theory. The surface settlements are obtained in the construction of the spatially curved section considering various parameters of pipe jacking and formation loss. The calculated results are compared with the measured surface settlements of the pipe jacking tunnel project of Panqiao substation, Ningbo, China. The results show that: (1) By considering the additional load caused by pipe jacking and horizontal and vertical overbreak clearances, the results from the proposed method agree well with the measured results, indicating that the proposed method can accurately predict the actual surface settlement. (2) The surface settlement groove caused by spatially curved pipe jacking is not symmetrical with respect to the central axis of pipe jacking. When there is no overbreak cutter on the cutterhead, the maximum settlement shifts to the outside of the curve, and the overbreak gap generated by plane turning of the pipe jacking machine can dramatically affect the deviation of the surface settlement groove. (3) During the pipe jacking process, the stratum loss causes most of the surface settlement. Therefore, the grouting parameters should be strictly controlled, and the theoretical grouting amount should be the sum of the grout volumes within the annular and over the excavation gaps.

Key words: S-shaped curved pipe jacking tunnel; Mindlin′s solution, random medium theory, surface deformation