Centrifuge modeling of excavation effects on a nearby tunnel in soft clay

The centrifuge modeling with a similarity ratio of 1∶120 is carried out to investigate the impacts of an excavation on a nearby tunnel in soft clayey strata. The responses of undrained shear strength, pore water pressures, horizontal earth pressures around the tunnel, ground settlements, tunnel settlements and bending moments are obtained. The test results show that: (1) The exposure of the excavation base leads to the continuous evolution of the excess pore water pressures of soils below the excavation base and around the tunnel, together with both the magnitude and distribution changes of horizontal earth pressures around the tunnel. (2) Using the effective vertical stress reduction ratio-based equation for soil disturbance degree (SDD), SDD of soils with vertical distances of 0.3 and 0.7 times the excavation depth below the excavation base are 0.33 and 0.21, respectively. (3) Due to the existing tunnel, the ground surface settlements behind the diaphragm wall mainly locate at Zone II predicted by Peck (1969). (4) After excavation, the ground surface settlements, tunnel settlements and bending moments develop continuously. The tunnel settlement at 815 days after excavation is 1.6 times that during excavation stage. The consolidation and creep may be the main reasons for the continuous development of tunnel deformations and internal forces after excavation, implying that the exposure time of the excavation base should be minimized in real projects.