【摘要】 进行了群桩基础可视化模型试验。在试验过程中对各级竖向荷载作用下群桩基础桩、土的变形采用高清晰数码相机拍摄了照片。通过对照片进行后处理分析,得到了桩、土的位移场,也对桩身轴力也进行了量测,在该基础上研究了群桩基础的变形性状和破坏模式,重点分析对比了桩间距和桩长对桩端土体沉降以及桩身侧摩阻力的影响。试验发现,桩距是影响桩土相对滑移量的主要因素,桩距越大,桩身与土的相对滑移量就越大,桩端刺入量也越大。在柔性筏基下,随桩距增加中桩的桩土相对滑移量可能会大于边桩。桩端刺入量是大桩距桩基础主要的沉降构成,以桩端刺入量为研究对象建立一套大桩距基础新的沉降计算理论,似乎值得进一步研究。桩顶向上刺入(可通过设置褥垫层、桩顶预留净空或设置可压缩垫块来实现)有利于桩间土的压密,减小桩端刺入量,甚至改变破坏模式。更多还原

【Abstract】 Model tests of piled raft are performed, the high quality digital pictures of displacements of soil and piled raft under each vertical load increment are taken during testing process. The axial forces of piles are measured. The detailed displacement fields of soil and piles are obtained by analyzing the digital pictures. Based on this, the failure mode and deformation behavior of the piled raft are studied. The effect of pile spacing and pile length on the settlement beneath pile tip and shaft resistance of pile is analyzed. Test results show that pile spacing is the major factor which has significant effect on the slip at the interface of pile shaft and surrounding soil. The piled foundation with bigger pile spacing produces larger pile – soil slip and pile tip penetration. The central pile under comparatively flexible raft can produce larger pile – soil slip and pile tip penetration than that of edge piles when pile spacing is large enough. The pile tip penetration accounts for most part of the settlement of piled raft with larger pile spacing. This implies that it’s necessary to construct a theory, where the pile tip penetration should be taken into account, to calculate the settlement of piled raft with large pile spacing. By laying a layer of sand cushion, compressible block, or simply a gap between raft and pile head to make it possible for the soil beneath raft to carry load first, the soil beneath the raft can be compacted before piles begin to carry load significantly and thus can reduce the pile-soil slip and pile tip penetration and even change the failure mode.更多还原