Abstract: Due to alignment requirement, a mined tunnel section of a new line of Guangzhou Metro should closely cross underneath a large underground commercial space. There are 5 pile foundations should be underpinned. As a result, the intunnel archshaped pile foundation underpinning scheme is adopted for various restraining factors such as large pile axial force, large tunnel span and complex field conditions. The empirical relationship between the height and width of underpinning structure crosssection and tunnel span and pile foundation axial force is revealed by engineering comparison; moreover, the structural internal force is analyzed by 2D loadstructure method and the deformation is simulated by 3D stratumstructure method, so as to verify the bearing capacity and normal service limit state of the underpinning structure. The results show that the intunnel archshaped pile foundation underpinning scheme is feasible in case of large pile loads and tunnel span, and the preliminary rules for the dimensions of the underpinning structure are applicable.

Key words: metro, mined tunnel, pile foundation underpinning, intunnel archshape underpinning, large span, large axial load