Centrifuge Modeling of Ground and Tunnel Responses to Nearby Excavation in Soft Clay

Excavations near an existing tunnel are frequently encountered in underground construction. The excavation–soil–tunnel interaction mechanism is not yet fully understood, notably the long-term behavior. This study carried out three-dimensional centrifuge test of an existing tunnel subjected to a nearby excavation in saturated kaolin clay. Emphasis is put on the long-term behaviors of the ground and tunnel regarding the undrained shear strength, excess pore-water pressure, horizontal earth pressure, compression behavior, settlement, and bending moment. T-bar penetration tests showed that the retaining wall installation leads to a soil strength increase, whereas the excavation causes a reduction. Excess pore-water pressure below the excavation base gradually dissipates to zero. In comparison, the excess pore-water pressures above the tunnel crown and nearby the right springline (close to the excavation) experience continuous increases, although those close to the left springline (away from the excavation) exhibit a different pattern. Reduction amplitudes in horizontal earth pressures around the tunnel differ in both burial depth and horizontal relative position. The lateral earth pressure coefficient nearby the right springline decreases, and the stable value is higher than the Rankine's active earth pressure coefficient. The compressibility of soils at the left side of the excavation (tunnel exists) was lower than at its symmetrical side, and the ground surface settlement is compared with empirical estimates concerning ground conditions and excavation geometries. Long-term responses show that the excavation base exposure leads to continuous and appreciable increases in ground settlement, tunnel settlement, and bending moment.