海上四桩导管架基础水平受荷离心模型试验

导管架基础广泛应用于海上风力发电和油气开发,水平向风、浪、流、地震等作用是导管架基础发生失效破坏的主要原因。通过离心模型试验针对饱和砂土地基中四桩导管架基础,研究其在沿边长方向和沿对角线方向水平静力作用下各基桩的内力分配、桩周土反力差异和变形特性。导管架基础沿对角线加载时基桩最易被拔出,其下压基桩的桩顶剪力、桩顶负弯矩和桩身最大正弯矩均较上拔基桩大,但二者的桩身水平位移相差不大。对于本文桩间距为5.8倍桩径的导管架基础,由于群桩效应及桩身上拔力降低了桩周土有效应力,沿边长加载时上拔桩在泥面下2.5倍桩径深度范围内的桩周土反力约为下压桩的60%,而沿对角线加载时上拔桩在该深度范围内的桩周土反力仅为下压桩的40%。沿对角线加载时下压桩与上拔桩在桩顶剪力、桩顶最大负弯矩、桩顶轴力及桩身最大正弯矩等参数之间的差别也明显大于沿边长加载情况。与单桩水平加载离心模型试验结果对比发现,同一深度处单桩的桩周土反力介于导管架基础上拔桩与下压桩的桩周土反力之间。

Centrifuge modelling on tetrapod jacket foundation subjected to lateral loads

Jacket foundation is widely applied in development of offshore wind power, oil and gas. The failure of a jacket foundation is mainly caused by the lateral loads of wind, wave, current, earthquake, etc. Two groups of centrifugal model tests on a jacket foundation loaded along the border and the diagonal respectively are carried out in saturated sand to investigate the distribution of internal forces, difference of soil resistance and deformation characteristics for piles. The test results show that the piles of a jacket foundation will be pulled out more easily under diagonal loading. Moreover, compared with the up-lifted pile, the downward-pushed pile bears larger shear force and the maximum negative bending moment at the top, and larger maximum positive bending moment of the pile shaft, and shows basically the same lateral deflection. As for a 5.8-diameter spaced jacket foundation, because of the pile group effect and the up-lifting force which reduces the effective stress in soil around the pile, the resistance of shallow layer soils around the up-lifted pile is 60% of that around the downward-pushed pile within the depth of 2.5-diameter below mudline under diagonal loading, which is only 40% of that under diagonal loading. These differences of shear force, the maximum negative bending moment, axial force at the top and the maximum positive bending moment of the pile shaft between the downward-pushed pile and the up-lifted pile under diagonal loading are also more obvious than those under diagonal loading. In comparison with these results of centrifugal model tests on a large-diameter single pile under lateral loads, it is found that the soil resistance for a single pile is between that for the up-lifted pile and the downward-pushed pile of a jacket foundation at the same depth.