Performance of X-section cast-in-place concrete piles for highway constructions over soft clays

This paper introduces a foundation treatment technique for embankments over soft clays called the X-section cast-in-place concrete pile (referred to as XCC pile), including its driving equipment, strengthening principles and construction technique. A program of large-scale instrumented XCC piled embankment field tests is conducted to investigate the soil response during the installation of XCC piles, and bearing capacities of the single XCC pile and the XCC pile-raft. Experimental results during installation of the XCC piles show that the XCC pile appears to generate larger displacement changes when it gives the same volume of displaced soil to a closed-ended circular pile; measured surface radial displacements are significantly lower than predicted values of R = R_ou, although the perimeter of the X cross section is larger than that of the circle with radius R_ou; the convex part and the convex part of the XCC pile have little influence on the normalized total stresses Δσ_r/σ′_v0 at the same level. Load-settlement of the single XCC pile and pile raft suggests that the XCC pile appears to provide considerably larger enhancement than the flexible or semi-rigid columns. At last, this study depicts the effective application of the XCC pile in pile-supported embankments over soft clays, clarifying the effectiveness and stability of XCC pile technology in controlling lateral deformations and enhancing the embankment.