桩端土刚度对桩侧阻力影响的数值分析
Numerical analysis of influence of stiffness of pile tip soil on shaft resistance
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摘要: 固定桩侧土层压缩模量,采用有限元方法计算分析了不同 桩端土层与桩侧土层压缩模量比 <> E b / <>Es 情况下单桩承载性状及桩周土体单元应力状态和位移的变化。结果表明:不同桩端土层刚度会使桩侧土中竖向附加应力产生变化,在同一桩顶位移情况下,桩端土层刚度越大,桩端平面以上桩侧高应力区范围也越大;随着桩端土层刚度增大,桩身下段一定范围内( 10 ~ 15 d )的桩侧阻力有所提高,桩端土层刚度对桩侧阻力具有增强效应。结合 桩端侧附近土体单元微体应力状态变化的分析表明,增强效应发生机理在于随 桩端土层刚度的增加,直接导致桩体受压破损侧鼓效应增强;同时,桩端土层对上部桩侧土体向下位移起到阻滞约束作用增强,致使桩端侧一定范围内土体围压增加,土体抗剪强度提高,桩侧摩阻力增大。Abstract: Under the fixed compression modulus of pile shaft soil, the finite element method is employed to calculate and analyze the changes in the bearing behavior of single pile as well as the unit stress status and displacement changes of the soil around the pile under the circumstances of different soil compression modulus ratios of pile tip to pile shaft. A conclusion is drawn that different stiffnesses of pile tip soil may change the vertical additional stress in pile shaft soil. Under the same pile top displacement, the greater stiffness of pile tip soil is, the larger high-stress area of pile shaft soil above the pile tip is. With the increase of the stiffness of pile tip soil, the shaft resistance in a certain range of lower pile shaft will develop. So the stiffness of pile tip soil has an enhancing effect on the shaft resistance. Combined with the stress analysis of the soil unit around the pile tip, the influence mechanism can be summed that the pressure damage and protruding effect of the pile is enhanced by the increase of the stiffness of pile tip soil. At the same time, the constraint effect of pile tip soil on the displacement of pile shaft soil is improve, so the confining pressure in a certain area of pile tip soil is increased and the shear resistance is strengthened, and the shaft resistance is also increased.