Abstract: Based on the pit excavation engineering in Shenyang， which sits atop the existing tunnels， the effect of shield tunnel segment joint was studied. In order to accurately reflect the opening of segment joint for additional load， threedimensional model was created in Flac3D， which simulating segment joint by embedded beam elements. The result indicate that uplift deformation scope of existing tunnel is about 20 times of the excavation width， maximum uplift is about 1593mm， minimum longitudinal radius of curvature is about 28248m. The opening and dislocation of radial segment joint are 067mm， 137mm respectively， all control target meet the engineering requirements. The surcharge of heap loading will guarantee the security of shield segments and joints during in the construction of pit engineering.

Key words: foundation pit engineering, down tunnel, segments joint, Flac3D, construction scheme