Bearing capacity of piles in layered soils. Part 1. Clay overlying sand

The paper summarizes investigations on jacked and driven piles in non-uniform soils consisting of clay and sand. Part 1 deals with the bearing capacity of piles penetrating through clay into sand whereas Part 2 discusses the case of piles in a sand stratum overlying clay. Preliminary tests on small model piles have been undertaken to study the effects on the point resistance of parameters such as the strength and thickness of a clay stratum, the strength ratio of soils in the two layers and the geometry of the layers. Based on these results, tests on a 76 mm diameter instrumented steel pile and a 36 mm diameter static cone penetrometer have been carried out for selected combinations of the variables involved.The test results are analysed to determine the influence of clay thickness and strength on the point resistance of piles in sand, expressed by a non-dimensional clay strength factor λ, and parameters influencing λ are discussed. The effect of layering on the shaft friction in sand and the radial stresses along the pile length are studied. The efficiency of small groups of model piles in layered soils is obtained. Field data are analysed, including scale effects, and simple design rules are suggested to estimate the bearing capacity of piles in layered soils.