基于透明土的静压楔形桩沉桩效应模型试验研究

楔形桩是一种可以有效提高桩侧摩阻力的纵向变截面异形桩，然而针对该变截面桩沉桩效应特性方面的研究却相对较少。基于透明土材料和粒子图像测速技术（简称PIV），开展静压楔形桩沉桩模型试验，测得沉桩过程中桩周土体的位移场变化规律；沉桩过程中桩周土体位移场由激光射入透明土材料，与透明土材料之间的相互作用产生的独特散斑场，通过CCD（charge-coupled device）电荷耦合元件相机成像处理而获得。同时进行了等截面桩的沉桩模型试验，并对等混凝土材料用量情况下楔形桩和等截面桩的沉桩效应进行对比分析。最后，将此试验结果与基于常规试验手段的静压楔形桩沉桩模型试验和圆孔扩张理论计算结果进行对比分析，验证了基于透明土材料的静压楔形桩沉桩模型试验的准确性和可靠性。研究结果表明，基于透明土材料和PIV技术可以有效地开展静压楔形桩沉桩模型试验研究；楔形桩静压施工过程中对桩周土的影响范围约为等混凝土用量等截面桩的1.2倍。

Model test on installation effect of tapered piles in transparent soils

Tapered piles are a type of piles with a variable cross-section, which can effectively improve the skin friction of the piles. Thus far, however, little effort has been made to investigate the installation effect of the tapered piles. By using transparent soil materials and the particle image velocimetry (PIV) technique, a series of model tests is conducted to investigate the soil displacement of the surrounding soil in installing a tapered pile. The displacement field of the surrounding soil is determined by analyzing the distinctive laser speckle pattern generated by the interaction between the laser and transparent soil when the light goes through the transparent soil. The images of the laser speckle pattern is obtained by CCD (charge-coupled device) camera and analyzed using the PIV technique. For comparison, a model test on the installation of a constant cross-section pile is also carried out and analyzed. Finally, this result is compared with those of the model test on the installation of a variable cross-section pile and the cavity expansion theory, showing the accuracy and reliability of tapered pile installation model test using transparent soils. The results show that the model test on installing a tapered pile in transparent soil can effectively simulate the installation process of a tapered pile, and the radius of influence due to tapered pile installation is found to be about 1.2 times that of the equal section pile installation.