Abstract: A case study is conducted on a shield tunnel of Beijing metro line 17 undercrossing the existing operating tunnel of the Beijing Capital International Airport Line with a small space to investigate the clay shock performance and its mechanism of controlling the settlement of the shield excavation gap filling. The physicomechanical test and numerical simulation calculation methods are adopted to investigate the tunnel deformation and the clay shock mechanism. The results show that: (1) The permeability significantly decreases with increasing clay shock slurry concentration; the synchronous grouting slurry could be prevented from flowing forward at a clay shock solution concentration of 400 kg/m3, and the best filling and supporting effects of the excavation gap are observed. (2) The clay shock slurry can reduce the friction between the shield shell and the surrounding soil by 50% and avoid the shear failure and the volume expansion caused by the overconsolidation of soil, thereby minimizing the influence on the existing tunnel in the process of undercrossing construction. (3) The settlement of the existing tunnel can be effectively reduced by using doublecomponent slurry with a cement〖KG-*5〗∶〖KG-*5〗sodium silicate ratio of 1〖KG-*5〗∶〖KG-*5〗1 for radial grouting within 15 rings after the shield tail passes. (4) The numerical simulation results reveal that the construction settlement can be significantly reduced when the excavation gap is filled with grout, and the stratum displacement along the tunnel axis can also be effectively inhibited.

Key words: shield tunnel, undercrossing with small space, clay shock method, laboratory test, numerical modeling