Further studies on the repeated loading of piles in sand
The work presented in this thesis concerns the behaviour of isolated piles subjected to repeated loading and placed at various depths in a medium dense sand upon which either static or cyclic surcharge acted. The piles, which were of laboratory scale, were instrumented by strain gauged load cells located along the inner surfaces of the pile shafts. The behaviour of tension as well as compression piles was examined. It was found that the behaviour of the pile was governed to a large extent by the repeated load level, the number of load cycles and the initial boundary stress conditions existing along the pile shaft. In compression, the pile life-span decreased when the embedment depth increased while the reverse trend was observed,for tension piles. The movement of both tension and compression piles decreased when the surcharge pressure was increased or was cycled, and it was of a minimum value when the upper repeated load acted in-phase with the higher surcharge pressure. For tests performed with static surcharge pressure, repeated loading was found to decrease the bearing capacity and the pulling resistance of the pile. The higher percentage of reduction was recorded for the tension pile. In contrast, after cyclic surcharge tests the pile capacity always increased. At any depth of embedment or surcharge pressure,' as the nun-her of load cycles was increased the shaft load of a compression pile increased up to a peak value then decreased gradually until it reached a limiting value. This limiting value increased when the load level, the pile depth or the surcharge pressure was increased and it was independent of the pile loading history. iii For a tension pile the shaft load decreased progressively as the number of cycles increased until failure occurred.