为研究单桩在桩顶预先施加竖向和弯矩荷载下的水平承载特性,通过自行加工的组合荷载加载装置,进行一系列室内单桩模型试验,分析砂土中预先施加的不同竖向和弯矩荷载对单桩水平荷载下的水平位移、桩顶转角、桩身弯矩以及地基比例系数m值的影响。试验结果表明：当预先施加的竖向荷载小于单桩竖向极限承载力的一半(Vu/2)时,相同水平荷载下单桩的水平位移有所减小,单桩的水平极限承载力得到提高,桩身最大弯矩有所减小,并且竖向荷载越大,越有利于单桩的水平承载性能；弯矩荷载的存在不利于单桩的水平承载能力,显著降低单桩的水平极限承载力；另外,水平荷载的施加对单桩的竖向位移影响较小；当砂面处水平位移较小时,m值随着水平位移的增加迅速降低,当水平位移增加到一定程度,m值减小的幅度越来越小,最后趋于一个稳定值。%The single pile is always loaded by the vertical,lateral and moment loads,rather than a single one and the bearing capacity of single pile is affected by the interaction among them. In order to study the behavior of lateral bearing capacity of single pile as different vertical and moment loads were applied on single pile before the lateral one,the special device for combined loads was designed and a series of model tests in sand were conducted to investigate the effects of vertical and moment load on the lateral pile top deflections,pile top rotation angle, bending moment and ground coefficient. For the piles under the vertical load less than Vu/2,the presence of vertical load improves the lateral bearing property of single pile,and lateral displacement and the maximum bending moment in pile decrease with the increasing of vertical load. However,the bending moment acted on the top of pile is harm to the lateral bearing property and the ultimate lateral bearing capacity is significantly deteriorated. The settlement is affected slightly by the lateral load when the vertical load is loaded previously. The ground coefficient decreases rapidly as the lateral deformation increases when the lateral deformation is small,and then decreases slowly and tends to be a constant value as the lateral deformation grows.
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