真空联合堆载预压下混凝土芯砂石桩复合地基固结特性理论分析

真空联合堆载预压与混凝土芯砂石桩复合地基相结合是处理深厚软土地基的一种新方法。该方法既能利用预制混凝土芯桩提高地基承载力，又能利用砂石外壳缩短排水路径、传递真空负压，加快固结。根据真空联合堆载预压下混凝土芯砂石桩复合地基的固结特点，将堆载预压和真空预压的固结效应分开考虑，然后再进行叠加，推导出了真空联合堆载预压下混凝土芯砂石桩复合地基的平均固结度解析解，并利用三维数值模拟对平均固结度解析解进行了验证。通过对解析解的参数分析，探讨了置换率、涂抹区大小及渗透系数、混凝土芯砂石桩长径比和芯桩率对混凝土芯砂石桩复合地基固结特性的影响。结果表明，混凝土芯砂石桩复合地基的固结速率随着置换率和芯桩率的增大而增大，随涂抹区和砂石外壳直径之比、未扰动区和涂抹区渗透系数之比、长径比的增大而减小。

Consolidation analysis of concrete-cored sand-gravel piles improved composite foundation under combined vacuum and surcharge preloading

a new ground improvement method is proposed to treat thick soft soil, which involves the use of concrete-cored sand-gravel piles with combined vacuum and surcharge preloading. In this method, the prefabricated inner piles are used to increase the bearing capacity of soft soil, and the outer sand piles are used to shorten drainage path, transmit vacuum pressures and accelerate consolidation of soft soil. According to the consolidation characteristics of the composite foundation improved by concrete-cored sand-gravel piles under combined vacuum and surcharge preloading, the analytical solutions of average degree of consolidation are derived by calculating the consolidation effects of the composite foundation under surcharge or vacuum preloading separately and then superposing them together. The effects of area replacement ratio of composite pile to soft soil, dimensions and permeability of the smear zone, length-diameter ratio of the concrete-cored sand-gravel column, and area ratio of the inner pile to the composite pile on the consolidation behaviors of the composite foundation are investigated by a parametric analysis based on the proposed solutions. The results show that the consolidation rate of the composite foundation increases with the increase of the area replacement ratio and the area ratio of the inner pile to the composite pile, and decreases with an increase of the diameter ratio of smear zone to composite pile, the permeability ratio of undisturbed zone to smear zone, the length-diameter ratio of the composite pile.