Field Study of Downdrag and Dragload of Bored Piles in Consolidating Ground

Abstract

This paper reports a field study on the downdrag and dragload of two pairs of bored piles installed in consolidating ground in the Zhejiang coastal area, China. During and after the construction of a 2.5-m-high embankment, the dragload and downdrag induced on the four piles, surface and subsurface soil settlement, pore water pressure, and lateral earth pressure were monitored. The field measurements show that the maximum dragloads in piles founded on relatively stiffer (end-bearing pile) and relatively softer layers (floating pile) ranged from 1,198 to 1,238 kN and from 798 to 870 kN, respectively. This suggests that the dragload in a floating pile can be one-third less than that in an end-bearing pile with similar geometries and embedded in the same consolidating ground. Deduced β values above the neutral plane (NP) in the clay strata ranged from 0.28 to 0.3, respectively. A much smaller β (0.04–0.06) was found below the NP. The existing analytical solutions overestimated the depth of the NP, leaving the structural design of the piles on the safe side.