预压软土地基对超长群桩承载性状的影响

Influence of preloading soft soil foundation on bearing behavior of super-long group piles

建立超长桩和土体共同作用的三维非线性有限元数值模型,采用预压排水固结法研究软土地基预压后超长桩的承载特性,分析地基土固结沉降、桩身侧摩阻力、桩顶位移-荷载曲线和桩身轴力的变化规律。通过运用控制变量法对预压时间和预压荷载以及不同土质的预压效果进行分析,对比分析单桩与群桩对预压效果的敏感度,并分析固结度对超长桩承载性状的影响。结果表明:预压能较好地改善地基、提高超长群桩的承载能力。增大预压荷载,可增大土体的固结沉降和桩身侧摩阻力;延长预压时间,可提高桩身侧摩阻力,减小桩顶沉降和桩身轴力;预压对群桩的影响好于单桩;固结度越大,超长群桩承载性能越好;对于粉质黏土、黏土以及淤泥质粉质黏土,当预压时间分别达到90 d及180 d时,地基固结基本完成,预压不再改变土的力学指标。

The three-dimensional nonlinear finite element numerical model of super-long pile and soil is established.The loading characteristics of super-long pile after preloading of soft soil foundation are studied by preloading drainage consolidation method,and the changes of soil consolidation settlement,side friction resistance of pile body,pile top displacement load curve and axial force of pile body are analyzed.The preloading time,preloading load and preloading effect of different soil are analyzed by the control variable method,the sensitivity of the single pile and the group pile to the preloading are compared and the influence of consolidation degree on the bearing behavior of super-long piles is analyzed.The results show that preloading can improve the foundation and the bearing capacity of super-long pile groups.The consolidation settlement of soil and the side friction resistance of the pile body can be increased by increasing preloading.Increasing the preloading time can increase the side friction resistance of the pile,reduce the settlement of pile top and the axial force of the pile.The effect of preloading on the pile group is better than on the single pile.The better the consolidation degree is,the better the bearing performance of the super-long pile groups.For the silty clay,clay and muddy silty clay,the consolidation of the foundation is basically completed when the preloading time reaches about 90 days and 180 days respectively,and the preloading no longer changes the mechanical index of the soil.