软黏土中成桩工艺对HSCM桩抗压承载性能影响的模型试验研究

Experiment on the compressive bearing performance of helix stiffened cement mixing piles embedded in soft clay influenced by the installed technique

螺旋桩芯劲性复合桩(helix stiffened cement mixing pile,简称HSCM桩)是一种新型复合桩,其成桩工艺会对桩身及其承载性能有较大影响。为验证HSCM桩在软黏土中同步旋进注浆工艺的可行性,并研究其成桩参数对抗压承载性能的影响,设计了2组缩尺模型试验,包括不同叶片数量与钻进速度的HSCM桩与对比螺旋桩。通过在高岭土制备的软黏土中成桩,并进行抗压承载性能及桩身几何尺寸测试,分析HSCM桩的成桩参数与水泥土桩身间的关系。试验结果表明:同步旋进注浆工艺能够在螺旋桩周围形成倒圆台状的水泥土桩身,水泥土桩身的平均黏结直径约为叶片直径的1.17~1.35倍;适当增加叶片数量能够使水泥与土体充分拌和,提高水泥土桩身的完整性与连续性,以改善HSCM桩的成桩质量;钻进速度大幅提高会导致注浆量不足,减小水泥土桩身的黏结直径与刚度;试验条件下HSCM桩的抗压极限承载力是螺旋桩的3.83~3.93倍,桩径扩大提高了侧摩阻力,注浆工艺加固并提高了土体强度,弥补了叶片在旋进过程中扰动土体造成强度降低的问题。

The Helix Stiffened Cement Mixing(HSCM)pile is an innovative type of composite pile,and the installation technique can affect the load bearing performance and bond diameter of the pile.To verify the feasibility of the simultaneous drilling and grouting techniques for HSCM piles in soft clay and to investigate the influence of the installation parameters on the compressive load bearing performance,two sets of model tests were designed in this study,including HSCM piles with different helix numbers and drilling speeds and comparative helical piles.The test piles were installed in the soft clay prepared from kaolinite clay and tested for compressive load bearing performance and pile geometry to analyze the relationship between the installation parameters of the HSCM piles and the soil-cement column.The test results showed that the simultaneous drilling and grouting techniques were able to form the soil-cement column with the shape of an inverted frustum of a cone around the helical pile,with the average bond diameter of the soil-cement column being approximately 1.17 to 1.35 times the helix diameter.An appropriate increase in the helix number could enhance the integrity and continuity of the soil-cement column by mixing the cement with the soil adequately to improve the installed quality of HSCM piles.Excessive drilling speed could result in inadequate grouting,which reduces the bond diameter and stiffness of the soilcement column.The compressive ultimate bearing capacity of HSCM piles under the conditions of this paper is 3.83 to 3.93 times that of helical piles.The enlargement of the pile diameter increased the skin resistance.The grouting technique was able to reinforce the soil and increase its strength,thus compensating for the reduction in strength caused by the disturbance of the soil by the helix plate during the rotary process.