Analysis of ground surface settlement induced by the construction of mechanized twin tunnels in soil-rock mass mixed ground

Abstract

The ground surfaces induced by the subway tunnel excavation has been an issue of great concern in the engineering field. When building subway tunnels in rugged mountainous cities, settlement problems are inevitable for shallow buried sections. Therefore, this paper analyzes the influence of some major tunnelling parameters on the surface settlement during excavation by creating a fine 3D FE model for the shallow-buried section of the Chongqing Metro Circle Line. Due to the lack of construction experience in the project area, the thrust force, backfilling pressure, backfill gravels and backfilling density of the right tunnel were suggested changeless as 6500 kN, 0.3 MPa and 85% separately based on similar engineering case. Simulations show that the settlement can meet the construction control requirements (<20 mm), then the construction parameters of the left tunnel were studied in detail under the condition of right tunnel excavated. The numerical computation results reveal that a tunnelling thrust of about 5000 kN and an average backfill gravels density of 89% of left tunnel corresponded to the minimum cumulative surface settlement. Finally, both the numerical prediction and field data show that the shape of surface settlement curves in the study area still follows the Gaussian distribution, which can provide a reference for other metro construction projects in this region.