SKIN FRICTION IN PILES UNDER TENSILE AND COMPRESSIVE LOADING

Abstract

In most soil types, it is generally assumed that the skin friction resistance of a pile is identical under both tensile and compressive loading. However, there is widespread experimental evidence that in sand the skin friction resistance is significantly lower for tensile loading than compressive loading. Laboratory model pile load tests under tensile and compressive loading were carried out and the results are presented for studying the behavior of skin friction. Model piles were specially designed to eliminate the presence of base resistance in compression test. Model steel pile (D = 2.5 cm and L/D = 20) with two type of surface characteristics - smooth and rough - were used in uniform medium dense sand (Dr = 38.1%) during the tests. Two methods of pile installation to represent bored and driven pile were adopted. Tests were conducted in dry, moist, and submerged conditions of sand. Based on the present model pile tests, the ultimate skin friction resistance, the displacement required for full mobilization in skin friction resistance, the ratio of skin friction resistance under tensile loading to that under compressive loading, Qs, / Qs„ and the coefficient of lateral earth pressure were determined and compared with the previously published data. The analysis of the data indicates that Qs, / Qs, is independent of the soil friction angle and a value of 0.85 in moist condition and 0.65 in submerged condition for this ratio is recommended for piles in sand.