Behaviour of laterally loaded piles is studied treating the soil medium as an elastoplastic medium. In the elastic range, the foundation reaction is incorporated in the analysis using the Winkler's hypothesis, while in the plastic range yield pressure of the soil is considered. Solutions are obtained treating the pile as a beam on elasto-plastic foundation. Different cases of boundary conditions of the pile are considered. The response of the pile is obtained in terms of dimensionless parameters and are presented in the form of figures. Results show a good agreement with the observed behaviour.

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Literature survey reveals that the undrained shear strength of cohesive soil (normally consolidated and saturated) will be anisotropic in addition to increasing linearly with depth. Bearing capacity of shallow strip footings on such deposits is analysed on the assumption of cylindrical failure surface and results obtained with a computer for a useful range of values of coefficients defining strength anisotropy, strength increase with depth and wall adhesion. Physical reasoning for the characteristics of failure surface such as the deepest level, lateral and vertical spread has been advanced in terms of the computed values of D/b and R/b. Separate charts presented for the bearing capacity factors due to strength anisotropy, strength increase and wall adhesion could be used to compute the composite bearing capacity factor as illustrated by an example.

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Field load tests were conducted on piles 20 cm in diameter in medium dense and dense sands. The piles were buried, jack-driven, or hammer-driven into the sands with depths of embedment from 4 m to 11 m, and loading cycles of 10- cm penetration were repeated until total settlement reached 5 to 9 pile diameters. Settlement of 1 to 1.5 pile diameters was required before the ultimate load was reached for the buried piles, whereas the required settlement for the diven piles was 0.1 pile diameter.During excavation of the test site after the pile load tests, the soil around the piles was observed, and undisturbed samples were obtained for laboratory tests. Detailed density measurements and grain size analyses on a block sample of dense sand directly below the pile tip showed that the sand underwent marked reduction in volume accompanied by considerable crushing of the particles, i.e., the dry density increased from 1.47 g/cm³ to a maximum of 2.0 g/cm³, and the minus 0.105 mm fraction increased from 17% to 65%.

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A 4-pile group of vertical, fiexible piles embedded in dense sand was subjected to cyclic lateral load, with and without vertical load acting on cap. Conditions of free rotation and no rotation of the cap were imposed. A single pile was also tested. Effect of cyclic load on horizontal deflection, rotation of cap and moments induced in the piles has been investigated. The deflection, rotation and moment were observed to increase at a decreasing rate with cyclic loading. Cap restraint reduced the corresponding changes. Effect of vertical load was not of significance.

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