Effect of jet grouting and dewatering on an adjacent tunnel in a Shanghai deep excavation

Abstract

In general, jet grouting is usually adopted in deep excavation projects to improve the soils inside and outside the pit to protect surrounding tunnels or building foundations. A cost-effective way is to keep the deformations caused by pit excavation within limitations with the minimum jet-grouting. In this study, different types of jet-grouting soils around tunnels or inside pits were compared and analysed in detail using three-dimensional finite-element modelling. Tunnels on one side of the pit or underneath the formation level were considered. A dewatering method was also introduced in some finite-element models to explore the effect of pore-water pressure (PWP) relief wells in soft clay with very low permeability. The finite-element modelling results indicated that enhancing the soils around tunnels is more profitable than only improving the soils between tunnels and retaining walls. The positive effect of jet-grouting soils above the tunnel may exert only when the excess PWP dissipates. This study may assist engineers who are seeking more cost-effective ways to protect surrounding tunnels or building foundations during deep excavation in soft clay.