Centrifuge modeling of effectiveness of protective measures on existing tunnel subjected to nearby excavation

摘要

Various countermeasures are adopted to mitigate nearby excavation-induced deformations and internal forces of an existing tunnel. The effectiveness and function mechanism behind the measures are not yet fully understood. In this study, three three-dimensional centrifuge tests are carried out to investigate the responses of the tunnel and ground due to a nearby excavation in dry sand. Soil improvement below the excavation base (cement-sand mixing column) and grouting around the tunnel (grouted body) are considered in these tests. It is found that, due to the excavation, earth pressures on the tunnel right springline and right heel decrease, while these on the left shoulder and left springline increase. Mindlin Green?s function underestimates the reduction magnitude of earth pressure on the right springline, but overestimates the tunnel heave and soil heave at the excavation base. Soil improvement, due to its restriction effects on the diaphragm wall and ground, achieves a desirable effectiveness on mitigating the ground settlements, earth pressure changes around the tunnel, soil heave at excavation base, tunnel heave and bending moments. In comparison, grouting around the tunnel also exhibits a certain degree of effectiveness, which might resulting from its effects on strengthing the tunnel-soil interactions.