Abstract: In order to solve the problem for safe implementation of C-shaped connecting gallery in the overlapping section of metro shield tunneling in complex environments and rich water sand layers, a segmented hidden excavation method with "first lower, then upper, and finally middle" as the construction process and a matching time-based and regional freezing auxiliary method is adopted. First, the thickness of the frozen wall and other main freezing parameters for each part are determined, and tests are conducted on the frozen soil to obtain the strength indicators for each layer of frozen soil. Strength verification is conducted on the frozen wall, and the verification results meet the safety factor requirements. Second, the ground vertical and horizontal freezing pipes inside the tunnel are reasonably arranged, and technical measures are used to reduce the impact of cross freezing and frost heave, ensuring the freezing effect. Then, preembedded grouting pipes are used in various parts of the connecting channel and thawing and settlement grouting are carried out from bottom to top, using the way of "multi-point, small amount, multiple times, and even" according to the thawing process, to control structural and geological settlement. Finally, the status of frozen walls, structures, ground, and surrounding environment during construction is monitored, providing guidance for construction correction. The results show that: by using the proposed method to construct the C-shaped connecting gallery, high strength of the frozen wall, good water sealing performance, small frost heave and thaw settlement, minimal structural deformation and impact on the surrounding environment can be achieved.

Key words: C-shaped connecting gallery, time-base and regional freezing, sub section excavation construction, thaw settlement grouting, monitoring measurement