Abstract: Excavation-induced unloading in deep foundation pits can generate undesirble deformation in adjacent operational tunnels, posing risks to structural integrity and service performance. This study documents a commercial complex project constructed in close proximity to an existing subway tunnel. A three-dimensional coupled excavation-tunnel model was developed using finite-element analysis, incorporating the small-strain soil behavior of soft ground and simulating the staged excavation process. The model was used to quantify the evolution of tunnel crown deformation throughout construction. Complementary field monitoring captured horizontal tunnel displacement and the response of adjacent soldier piles. Results indicate that installation of a water-stop curtain effectively stabilized the hydraulic regime, with negligible variation in total head beneath the existing tunnel. Excavation activities produced substantially greater impacts on horizontal displacement, ground settlement, and tunnel deformation than subsequent backfilling or superimposed surface loads. The most significant effects were confined to the excavation influence zone, with maximum deformation occurring near the excavation centerline. Upon completion, measured soldierpile deflections and tunnel deformations remained within allowable limits, demonstrating that the adopted support system provided effective control of excavation-induced tunnel movements.

Key words: Soft Soils, Deep Excavation, Adjacent Existing Tunnels, Deformation Pattern