Abstract: When tunnel boring machine (TBM) tunneling in composite rock strata with more than two lithologies, the tunneling parameters vary, and differential settlement occurs, which would cause ground settlement and further affect the adjacent buildings. As a result, a case study is conducted on a composite rock tunnel project between Central Park East station and Congyansi station of the second phase of Chongqing railway line 9, which is characterized by large longitudinal span and strong rock heterogeneity. A suite of key technologies for the TBM construction in composite rock strata is summarized, which follows the principle of composite TBM construction, left hole excavation first, TBM parameter optimization, synchronous grouting (secondary grouting), monitoring, and warning judgment. The settlement of buildings crossed by right line of tunnel has been controlled effectively, which guarantees the successful underpass of the TBM tunnel in a highefficient and quality manner and as well as the safety of the existing structures.

Key words: composite rock tunnel, crossing underneath existing building, composite tunnel boring machine, monitoring measurement, settlement control