Abstract: In view of reality of small working surface and large depth of foundation pit when a deep foundation pit is excavated in shield shaft, a prefabricated concrete filled tube (PCFT) internal bracing structure is presented. The PCFT internal bracing consists of lightweight aggregate concrete members and anchors composed of double-limb rectangular steel tubes, and assembled by high-strength bolts.Taking the deep foundation pit project of a shield shaft in Beijing Metro Line 17 as background, research on the design and application of PCFT internal bracing foundation pit support were carried out. In the study, the information monitoring of supporting axial force, retaining pile deformation, pile top displacement and surface settlement was also carried out. The design technology of PCFT internal bracing is summarized and optimized later in engineering practice. The implementation effect and monitoring results show that erection construction technology of PCFT internal bracing is simple and easy. On the basis of effectively controlling the stability of the foundation pit and the safety of the surrounding environment, the PCFT internal bracing greatly improves the safety and convenience of shield shaft deep foundation pit construction.

Key words: deep excavation of shield shaft, bracing of pit supporting, concrete-filled tube, prefabricated structure