上拔荷载对斜桩水平承载性状影响的试验研究

斜桩在承受水平荷载的同时,往往会受到上拔荷载的作用。为研究上拔荷载对斜桩水平承载性状的影响,开展了10根直、斜桩的室内模型试验,研究上拔荷载对斜桩桩顶水平位移和水平承载力的影响,对比了直桩与斜桩桩身弯矩和剪力的差异,并分析了上拔荷载对正、负斜桩桩身内力及桩侧摩阻力的影响规律。模型试验结果表明:上拔荷载从直桩水平极限承载力的12.5%增大到75%时,正斜桩水平承载力比增大21%,负斜桩水平承载力比减小25%。上拔荷载的存在会使正、负斜桩桩身轴力均增大,且上拔荷载越大,桩身轴力越大。上拔荷载能减小正斜桩桩身弯矩和剪力,使其抵抗弯矩和剪力的能力得到提高,而增大负斜桩桩身弯矩和剪力,使其抵抗弯矩和剪力的能力被削弱;不论正斜桩还是负斜桩,其上部区段桩身侧表面均出现了方向向上的摩阻力,而下部区段桩身侧表面均为方向向下的摩阻力,随着上拔荷载的增大,斜桩桩身侧摩阻力逐渐增大。

Experimental Study on Influence of Uplift Load onHorizontal Bearing Behavior of Batter Piles

Batter piles are subjected to horizontal loads and meanwhile uplift loads. To investigate the influence of uplift load on the horizontal bearing behavior of batter piles, we conducted indoor model tests on two groups of batter piles subjected to different uplift loads and vertical pile subjected only to horizontal load as control group. According to test result we examined the effects of uplift load on horizontal displacement and horizontal bearing capacity of the top of batter pile, compared the bending moment and shearing force between vertical pile and batter pile, and also analyzed the effects of uplift load on the internal force and frictional resistance of positive and negative batter piles. When uplift load increased from 12.5% to 75% of the horizontal ultimate bearing capacity of vertical piles, the horizontal bearing capacity ratio of positive batter piles increased by 21% while that of negative batter piles decreased by 25%. Uplift load augmented the axial force of both positive and negative batter piles. The larger the uplift load, the greater the axial force of pile. Uplift load also reduced the bending moment and shear force of positive batter piles, hence improving their ability to resisting moment and shear force, while weakened the ability of negative batter piles to resisting bending moment and shear force by increasing the bending moment and shear force. Both positive batter piles and negative batter piles witnessed an upward frictional resistance on the lateral surface of the pile body in the upper section, and downward frictional resistance in the lower section. With the increasing of uplift load, such side frictional resistance increased gradually.