Effect of assembled H-shaped steel struts with servo system on the safe excavation of a subway station

This study introduced the innovative design of assembled H-shaped steel strut (AHSS) with servo system for the deep excavation of a T-shaped subway interchange station in soft soil. Through the analysis of field monitored axial force of strut, the horizontal displacement of retaining wall, the ground surface settlement and the displacement of nearby existing tunnel, it was found that the servo system could provide convincing stable axial force for each level of AHSS. When a new level of AHSS with servo system was put into operation, the axial force of the closest level of concrete strut above tended to be affected greater than the other levels of strut. The 1st level of concrete strut contributed much less to resisting horizontal displacement of diaphragm wall than the other levels of strut, and was under tension during the later stage of excavation. The maximum horizontal displacement of diaphragm wall, displacement of the existing tunnel and ground surface settlement were all controlled well with the operation of AHSS with servo system. Meanwhile, stricter control of the horizontal displacement for diaphragm wall in the early stage is considered to be beneficial to the control of the further deformation of excavation in the later stage.