Axial capacity of bored piles in very stiff intermediate soils

There is a major shortage of good-quality load test data for bored piles in stiff to hard intermediate soils such as silts and clayey sands. This paper presents the results and interpretation of an instrumented pile test in a very stiff overconsolidated fine-grained deposit. It is shown that, unlike typical fine-grained soils, dilation at the shaft of the pile makes an important contribution to the unit shaft friction. The relationship between shaft friction and the cone penetration test (CPT) end resistance is observed to differ appreciably from established empirical correlations for bored piles in less stiff, fine-grained soils. This is inferred to be largely because of the similarity between the drained and undrained CPT resistances in this soil type as well as the influence of dilation. Existing empirical methods to assess end bearing of bored piles are also seen to provide inconsistent estimations in this soil type.