桩主要被用来传递竖向荷载，在码头结构中桩还常被用来承受横向荷载，抵抗地基侧向变形。侧向承载桩受到的作用力主要来自挡土陆侧和临空海侧之间的土压力差，但由于受力机理复杂，至今尚无成熟计算方法能够准确估算桩所承担的横向作用力。通常假设一个桩体等效作用宽度，然后采用挡土墙经典土压力理论进行计算，现行板桩码头结构设计中假设桩体作用宽度为2倍桩宽，然而，这种经验算法经常受到质疑，迫切需要试验验证。为了改进和完善现行的板桩码头结构设计计算方法，针对桩体作用宽度这一问题，设计开展了多组大型土工离心模型试验，通过微型土压力盒测量了不同桩间距布置的桩体侧面的土压力，获得了桩身前后两侧沿深度的土压力分布。试验结果表明，桩排中的单根桩作用宽度与桩间距密切相关，在桩间距宽度比d/b小于4.0时，其作用宽度系数keq近似与d/b线性递增；d/b大于4.0后，keq值逐渐趋于常值，不再随着d/b值出现非常明显的变化；对于桩间距为2倍桩宽（d/b=2.0）这一常见布置情形，实测桩体作用宽度系数keq值不足2.0。

Piles are mainly used to transfer vertical  loads  in soil ground. They are also frequently employed in port engineering to bear lateral thrust and to resist lateral deformation in the soil ground. As the horizontal load undertaken by a lateral bearing pile is not only through its shaft friction but also through the pressure difference between the retaining landside and its opposite seaside, the concerning mechanism is so complicated that so far there is no sophisticated procedures to exactly calculate the lateral action. In the current design practices of sheetpile bulkhead, lateral loading pile is simplified as a retaining wall with an equivalent breadth assumed to be equal to twice the pile’s width. The validity of such empirical method, however, is widely questioned; hence an investigation is needed to verify its effectiveness. An investigation by means of centrifuge model testing is carried out to determine the influence of ratio of space to width on equivalent breadth of one pile. Miniature earth pressure cells are installed on both sides of the pile to measure the distribution of pressures. Close correlation is found between the equivalent breadth of one pile and the ratio of space to width: the equivalent breadth ratio keq is approximately linearly increased with the ratio of space to width d/b as long as the value of d/b is less than 4; when the value of d/b exceeds 4, the value of keq is progressively proceeding to a constant, without significant change. In the common case of d/b=2, the observed value of keq is less than 2.0.