Interaction between a newly excavated underground ramp and deep existing tunnels

The close underground excavations inevitably become a common issue in large cities. The proximity of new excavation to existing structures changes the stress-strain regime of soil and can impose a considerable amount of load on nearby structures. A recent excavated case of an underground ramp that eases the access from underground tunnels to aboveground roads provided the chance to study proximity underground excavation and its effect on nearby structures. The ramp was excavated from the ground surface using an earth pressure balanced machine and after passing of a spiral route, it approaches and then connects to a deep existing target tunnel. The lining deformation of the target tunnel monitored before and after the passing of the excavation machine through several monitoring sections along the excavated ramp. The results of the previously performed beam-spring model related to this close excavation are presented. The proximity case of underground constructions is also simulated numerically and verified with measurement results. The verified numerical model is employed to predict the changes in the horizontal earth pressure acts on the target tunnel before and after passing of the machine in the last monitoring section of the ramp when the ramp and target tunnel are almost parallel. The results showed that among the horizontal earth pressure and internal structural forces in the target tunnel, the amount of bending moment changes as large as 35% by close excavation of nearby new tunnel.