海洋高桩基础水平单调及循环加载现场试验

开展了海洋软黏土中 2 根大直径高桩基础的现场水平单调和循环加载试验，实测获得了桩顶荷载 – 位移关系、桩身变形和桩身弯矩及桩侧土压力和孔隙水压力，揭示了水平单调和循环荷载作用下桩土相互作用规律及桩基水平位移和桩身弯矩发展规律。利用实测桩身水平位移推算了桩周土反力，在此基础上提出了相应的双曲线型 p – y 曲线，通过引进 Poulos 循环弱化模型建立了水平循环荷载作用下的桩基双曲线型 p – y 曲线分析模型，水平单调及循环荷载作用下桩顶荷载 – 位移关系、桩身变形和桩身弯矩及桩侧土压力等计算结果与实测值均吻合良好。通过现场试验发现规范 p – y 曲线法计算结果偏保守的主要原因是所采用的 p – y 曲线的刚度偏小；不同时段的循环荷载对桩基循环累积变形有叠加效应。 建议设计中应考虑桩基全寿命服役期内所承受的所有循环荷载的影响， 对于重要工程应开展相应的现场水平加载试验，实测桩身水平位移或桩身弯矩，进而利用所推算的桩周土反力来分析桩基受力变形及承载力。

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.