考虑桩底沉渣的随钻跟管桩竖向承载特性模型试验研究

随钻跟管桩施工不能完全清除桩底岩土沉渣,从而影响桩基端承力。为揭示桩底沉渣对随钻跟管桩承载力的影响机制,开展了考虑桩底沉渣影响的随钻跟管桩竖向承载特性模型试验研究。试验结果表明:在密砂地层中,具有桩端水泥土扩大头的随钻跟管桩,其桩顶荷载-沉降曲线为缓降型,而模拟试验的其他管桩均为陡降型;桩底沉渣降低随钻跟管桩的极限承载力在22%以内,且其桩顶荷载主要由桩侧摩阻力承担,承担占比超过90%;与存在一定厚度沉渣的钻孔灌注桩相比,随钻跟管桩的桩底沉渣对降低承载力的影响相对较小;靠近桩端的轴力随着沉渣厚度的增加而减小,沉渣越厚,减少的幅度越明显;桩端水泥土扩大头施工可提高随钻跟管桩约37%的承载力,且桩端阻比均小于15%。现场原位测试(桩长为15.5 m,长径比为15.50)和室内模型试验(桩长为1 m,长径比为15.87)结果均表明:存在桩底沉渣时,随钻跟管桩是以发挥侧摩阻力为主的端承摩擦型桩。研究成果有助于进一步加深对随钻跟管桩承载性状的认识。

An experimental study of vertical bearing capacity of DPC piles considering sediment effect at pile bottom

The pile bottom sediments cannot be cleaned up completely during the construction process of drilling with pre-stressed concrete pile cased(DPC) piles, which may lead to the loss of bearing capacity of the pile. Model tests for DPC piles with consideration of the pile bottom sediment effect are carried out in this paper. The load-settlement curves of DPC piles with enlarged cement-soil pile end show slow-varying, while other tests of DPC piles with pile end sediments show sharply down. The influences of the sediment thickness and enlarged pile end on the vertical bearing characteristics are studied. Experimental results show that the pile end sediment has a certain impact on the vertical bearing capacity of the DPC pile, and its bearing capacity can be improved by around 22% after removing the sediments. Compared with the bored cast-in-place pile with a certain thickness of sediment, the sediment at the bottom of DPC piles has less effect on reducing the bearing capacity. Besides, DPC piles with expanded cement-soil pile end can increase the bearing capacity by 37% in approximation. The external load of the DPC piles with pile bottom sediments is generally borne by the pile side frictions for more than 90%, and the pile axial forces near the pile end become smaller with thicker sediments. In dense sand strata, the pile end resistance ratios of DPC piles are less than 15%. Both in-situ(pile length 15.5 m, pile length-diameter ratio 15.50) and indoor model test(pile length 1.0 m, pile length-diameter ratio 15.87) results show that DPC piles with pile bottom sediments are the type of end bearing friction piles. These research findings may provide a reference for further understanding the bearing characteristics of DPC piles.