Behaviour of large scale rigid model piles under inclined loads in sand

Attention has been directed towards the stability of offshore structures since the discovery of oil under the sea bed in the 1920’s. Especially important in this field of engineering are the large lateral loads from wind, waves, and currents in conjunction with vertical loads. This combination of loads creates the need to analyze systems exposed to large inclined loads. – The scope of this research is to understand the behavior of a vertical rigid short pile under inclined loads in dense sand. The pile behavior under inclined loads has been examined in the laboratory using relatively large circular model piles of 75 mm, 90 mm, and 102 mm diameters and a square pile of 73 mm width. These model piles were instrumented with pressure transducers and load cells in order to measure soil pressures. The piles were tested with vertical, inclined, and horizontal loads using a computerized data acquisition system. For these model pile tests a suitable laboratory test frame and a circular steel soil container were designed and assembled. – As part of the comprehensive test program, the piles were first subjected to vertical loads. The bearing capacity factor Nq was found to be constant with depth and consistently smaller than that predicted by various existing theories. For a smooth circular pile the pull out resistance can be estimated as the sum of one half the downward skin friction plus the weight of the pile. – For computing the ultimate lateral load on circular piles, modification of existing theories is necessary to take into account the parabolic soil pressure variation across the projected pile diameter, rather than the rectangular distribution which is conventionally assumed. – The ultimate load capacity under inclined loads does not decrease uniformly with load inclination. For angles up to about 35°, the ultimate load capacity is larger than the vertical load capacity.