Enhancing Base Stability of Deep Excavation in Soft Clay with Grout Piles

Abstract

Excavation in soft clay layer often causes large ground movement around. Without proper control, a base heave failure may also occur when the strength of in-situ clay is low and the excavation goes too deep. To reduce the potential of such adverse consequence, grout piles installed by hydraulic or mechanical method are often used to increase the strength of in-situ clay. But the effect of grout piles reinforced soft clay is not easy to be properly quantified. This study adopted a laboratory model test which used very soft clay as the testing soil to generate large ground movement under 1-g condition. The test results indicate that not only the amount of ground movement and soil strains but also the extents of soil movement can be reduced by reinforcing the base of excavation with grout pile in soft clay. By adjusting the excavation induced ground movement with various grout pile spacing, the effectiveness of ground improvement and the amount of base heave can be evaluated. In general, the amount of base heaving decreases with the improvement ratio (Ir), but increases with the excavation width (B) for braced excavation.