Effect of sand compaction pile installation on strength of soft clay

In the design of sand compaction piles, the increase in undrained shear strength of the soft clay around the sand piles is often ignored. This paper examines the long-term gain in strength in the soft clay using centrifuge modelling and finite-element analysis. Stress, pore pressure and strength measurements in the centrifuge models are used to benchmark the finite-element results. Parametric studies are then conducted using finite-element analyses to explore the effects of the friction angle and modulus of the soft clay on the trend and quantum of strength increase. The findings show that the ratio of improved strength to original shear strength decays as a function of the logarithm of radial distance. A method of estimating strength increase is proposed, based on two parameters that are related to the friction angle and modulus of the soil. For multiple piles driven with almost no time lag for pore dissipation, strength gain does not accumulate with successive piles. On the other hand, if there is sufficient time for pore pressure dissipation between the driving of successive piles, the strength gains from the successive piles can be accumulated.