Analysis of vertically loaded jet-grout-pile-strengthened piles of expanded cross-section

Abstract

Piles are often installed together with jet grouting – to form a jet-grout-pile-strengthened pile – in soft subsoil regions of China to increase bearing capacity and reduce project costs. To facilitate their design, this paper presents a load-transfer approach to model the non-linear behaviour of such piles with expanded cross-sections. Three interface models are introduced to describe the interactions between soil–cement, the core pile and natural soil. Force equilibrium and displacement compatibility expressions are established and implemented through a purposely designed spreadsheet. The approach was verified by loading tests on two well-instrumented piles. A parametric study shows that having one to three segments of thick soil–cement enables a 20–60% gain in bearing capacity and a 43–55% reduction in head settlement compared with the core pile itself, which is slightly affected by the soil–cement modulus and stiffness ratio. It is cost-effective in practice to adopt two to four segments of soil–cement with a thickness of 0·1 m to a radius of core pile, an ultimate compressive strength of the soil–cement of over 2 MPa and a stiffness ratio of over 100 to reduce settlement. Finally, a simple equation is proposed to estimate the ultimate bearing capacity of such piles, which was verified by loading tests on piles in three case histories.