Field tests on lateral monotonic and cyclic loadings of offshore elevated piles

A series of field tests on lateral monotonic and cyclic loading are carried out for two offshore large-diameter elevated piles in soft marine clay. Force-displacement relationships of the pile heads, deformation and bending moment of the pile shaft as well as soil pressures and pore water pressures at the sides of the piles are measured. Based on the measured results, the soil-pile interaction and both of the deformation and the bending moment of the pile shaft under the lateral monotonic and cyclic loadings are studied. By calculating the soil reaction force based on the measured lateral displacement of the pile shaft, hyperbolic p – y curves for the test elevated piles are presented, and then a Poulos reduction coefficient is introduced to give the hyperbolic p – y curves under the lateral cyclic loading. Good agreement is found between the test results and the computed ones by the proposed hyperbolic p – y curves method. The main reason why the results of API p – y curves are underestimated is that the stiffness of the used p – y curves is too small. It is also found that the cyclic loadings at different stages have superposition effect on the accumulative deformation of the pile shaft, and their influence on the pile foundation should include all cyclic loads during the whole life of service. It is recommended to carry out field tests on lateral loading to measure the lateral displacement or bending moment of the pile shaft to deduce more accurate soil reaction force or p – y curves on the piles for an important project.