欠压实斜坡桩竖向承载特性离心模型试验研究

Centrifugal model tests on vertical bearing characteristics of undercompacted slope piles

现有的桩基理论与经验基本上是基于平坡条件下建立的,而工程中常见的欠压实斜坡桩的受力特性与平坡桩基存在着较大差异。基于斜坡桩的受力特点,开展了3组离心模型试验,研究了欠压实斜坡基桩在竖向荷载作用下的承载特性,获得了桩侧摩阻力、桩身轴力、桩体竖向位移的分布特征以及桩周土体的沉降规律,分析了边坡填筑压实度、坡比等因素对桩土非协调变形的影响。主要研究成果为:①欠压实斜坡基桩桩体受力主要包括桩侧正摩阻力、桩侧负摩阻力、桩端端阻力及边坡土体对桩体产生的下滑力等4部分。②桩周土体压实度对桩侧摩阻力沿深度分布及桩端阻力影响较大;斜坡坡度对桩侧摩阻力沿同截面桩身分布及侧阻力的峰值影响较大。③斜坡桩负摩阻力中性点约在0.5~0.6倍桩长埋深处,若按常规的承载桩基进行设计,桩体额外承受的负摩阻力和侧向荷载容易引起桩体破坏。

The existing theories and experience of pile foundation are based on the flat slopes,and the stress characteristics of undercompacted slope piles are quite different from those of flat slope piles.Based on the stress characteristics of slope piles,three groups of centrifugal model tests are carried out to study the bearing characteristics of foundation piles under vertical loads.The distribution characteristics of side friction resistance,axial force,vertical displacement of piles and the settlement laws of soils around the piles are obtained.The influences of compaction degree and slope ratio on the uncoordinated deformations of the piles and soils are analyzed.The results are as follows:(1)The stress of the undercompacted slope piles includes the positive friction resistance at the pile side,the negative friction resistance at the pile side,the resistance at the pile end and the sliding force of the slope.(2)The compaction degree of soils has a great influence on the distribution of pile side friction along the depth and pile tip resistance.The slope gradient has a great influence on the distribution of pile side friction resistance and the peak value of side resistance.(3)The neutral point of the negative friction resistance of the slope pile is about 0.5~0.6 times the length of the pile along the burial depth.According to the conventional design,the additional negative friction resistance and lateral load of the piles are easy to cause pile damage.