软黏土中导管架基础水平循环加载离心模型试验

Centrifuge modelling of jacket foundation subjected to cyclic lateral loading in soft clay

为研究海上风机四腿导管架基础在风、浪等水平循环荷载作用下的受力及变形特性,开展了近海饱和软黏土地基四腿导管架基础水平循环加载离心模型试验。实测获得了水平循环荷载下导管架顶部的位移、基桩顶部的水平位移以及桩身弯矩,并利用实测桩身弯矩推导出桩身变形与桩周土反力。试验结果表明:水平循环荷载作用下导管架顶部的荷载–位移曲线表现出明显的非线性;后排桩的水平位移约为前排桩的80%,且均小于导管架顶部的水平位移,导管架发生了一定角度的倾斜;桩身最大弯矩值出现在泥面下约6D深度处。在此基础上,采用双曲正切型p–y曲线方法拟合试验结果并与API规范作对比,发现API规范p–y曲线的初始刚度和极限土反力均偏小。试验进一步揭示了泥面下5D深度范围内需考虑桩周土反力的弱化现象,且前排桩周土反力的弱化程度明显大于后排桩,在工程设计时应分开考虑下基桩桩周土的强度弱化情况。

The centrifugal model tests are carried out on a jacket foundation subjected to cyclic lateral loading in saturated soft clay to investigate the force and deformation characteristics of the jacket foundation under cyclic lateral loading from wind and wave. The forces and displacements of the jacked top, displacements of piles head and bending moments of the pile shaft are measured. Based on the measured bending moments, the lateral displacements and the soil reaction forces around piles are calculated. The test results show that under the cyclic lateral loading, the load-displacement curve of the jacket foundation head exhibits an obvious nonlinearity. The lateral deformation of the trailing-row piles is about 80% of that of the leading-row ones, while both of their deformations are less than those of the jacket top, which leads to a certain angle of inclination on the jacket foundation. The peak bending moment of piles appear around 6 D below the soil surface. The hyperbolic tangent p-y curves are used to fit the test results and they are compared with the API code. It is found that the initial stiffness and ultimate shallow layer soil reaction are smaller, and the calculated results are too conservative according to the API code. Furthermore, it is revealed that the cyclic degradation of the soil reaction under soil surface within 5 times the diameter in depth should be taken into account, and the degradation of the leading-row piles is obviously larger compared with that of the trailing-row ones, which should be separately considered in engineering design.