Abstract: The crosssection of mined constructions spanning beneath existing buildings/structures gradually increases with time. Undercrossing systems and deformation control measures should be studied to manage the deformation of existing buildings/structures and ensure construction safety. In this study, the deformations of existing buildings/structures undercrossed by Phase Ⅲ Qianmen station of Beijing metro line 8 with various schemes are compared. Furthermore, key deformation control measures such as pipecurtain construction, pilot tunnel construction, and pile foundation deformation control are proposed. Finally, numerical simulations and field tests are performed to analyze the feasibility of combining pipecurtain, deephole grouting, and flatroofed 4pilot pilebeamarch PBA methods. The results show the following: (1) The deformation induced by large crosssection construction is greater than that induced by small crosssection construction; however, the deformation of large crosssection construction can be successfully managed by adopting appropriate schemes and methods. (2) The combined scheme of pipecurtain, deephole grouting, and flatroofed 4pilot PBA methods exhibit an appreciable deformation control capacity, which is practical in nonclose undercrossing constructions. (3) The entire process control is necessary.

Key words: large crosssection flatroofed station, nonclose mined undercrossing constructions, deformation control, numerical simulation, pipe curtain, 4pilot pilebeamarch (PBA) method, entire process control