Influences of construction of foundation pits on deformation of adjacent operating tunnels in whole process based on monitoring data

Due to the deformation of operating subway tunnels near foundation pit, the normal use and safe operation of subway tunnels are adversely affected. Based on the monitoring data of deformation of a subway tunnel near operation during the construction of foundation pits, the whole process of tunnel deformation from the envelope construction of foundation pits to the end of excavation is analyzed. The results show that the TRD construction has a soil-squeezing effect on the adjacent tunnel, and the tunnel presents a deformation mode of "horizontal contraction and vertical stretch". The displacement of the tunnel towards the foundation pit is caused by the construction of three-axis cement mixing pile. The construction of underground diaphragm wall is equivalent to the unloading effect on the adjacent tunnel, and the tunnel presents the deformation mode of "horizontal stretching, vertical contraction ". The settlement of ballast bed generated by the gap between enclosure structures and excavation of the foundation pit accounts for the largest proportion of the total ballast bed settlement, reaching 70.24%. The increment of horizontal displacement of the tunnel is the most prominent in the construction stage of the envelope, accounting for 43.81% of the total horizontal displacement. The increment of tunnel convergence is the largest in the excavation stage of the foundation pit, accounting for 55.26% of the total tunnel convergence. It is suggested that the deformation control measures at different construction stages should be formulated according to the development law of tunnel deformation in similar projects, so that the deformation of the adjacent tunnels can be in a safe and controllable range.