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进行砂土的单桩和2×2群桩的压、拔试验,测定桩身轴力、桩顶荷载、位移以及桩端阻力。试验研究结果表明,群桩的抗压群桩效应系数η>1,最优桩间距为4D(D为直径),对应的η约为1.2;桩端阻力群桩效应系数Bη大于桩侧摩阻力群桩效应系数sη,其最优桩间距为5D,对应的Bη值约为1.3;桩侧摩阻力群桩效应系数在3D时约为1.2,但随桩间距的增大而减小。与前人理论分析的结果不同,由于砂土的挤密效应,试验测得抗拔群桩效应系数也大于1,最优桩间距在4D~5D之间,系数约为1.2。桩间距为7D时压、拔群桩效应系数均趋近于1,可基本忽略群桩效应。
Sand and single pile 2 × 2 groups of pile pressure and pull tests to determine the axial force of the pile, pile top load, displacement and pile end resistance. The experimental results show that the pile group has a compressive effect of pile group with η> 1 and 4D (D is the diameter), and the corresponding η is about 1.2. The pile group resistance coefficient Bη of pile tip resistance is larger than that of pile side friction The pile group effect coefficient sη, the optimal pile spacing is 5D, the corresponding Bη value is about 1.3; Pile side pile resistance coefficient at 3D is about 1.2, but decreases with the increase of pile spacing. Different from previous theoretical analysis, due to the crowding effect of sand and soil, the coefficient of anti-pull group pile effect measured by the experiment is also greater than 1, and the optimal pile spacing is between 4D and 5D with a coefficient of about 1.2. When the pile spacing is 7D, the effects of pressure and pull-out pile are close to 1, and the pile-group effect can be basically neglected.