真空-堆载联合预压条件下复合地基固结理论研究

Based on the existing consolidation theories of vertical drain ground with vacuum-surcharge preloading and composite ground, the composite ground is chosen to be the object in this study according to the principles those the external load undertaken by column-soil together and the equivalent relationship of the seepage discharge to the volumetric change. The calculation models for the different consolidation problems are established, and which can consider some influencing factors existed in practical engineering, such as the time-dependent vacuum-surcharge preloading, the variation of horizontal permeability coefficient of soil due to the column construction, the permeability of column, the depth-dependent characteristic of initial excess pore water pressure caused by the transfer law of positive and negative pressure in ground, the deformation of column-soil, the composite ground with partially penetrated column and the non-linearity of soil. The detailed studies are made on the consolidation theory of composite ground under vacuum-surcharge preloading using the new solving conditions and the methods of analytical solution and numerical calculation. The influence of these factors on the consolidation behavior of the composite ground is investigated comprehensively. The comparative study on characteristics and differences between the consolidation theory of composite ground under vacuum-surcharge preloading and the ones of vertical drain ground with vacuum-surcharge preloading and composite ground is made. The rationality and applicable scope of these consolidation theories are discussed. The curves and diagrams of the consolidation calculation are drawn, and which can be available for reference use in practical engineering. The achievements in this study are obtained to enrich the consolidation theory of ground with vacuum-surcharge preloading and composite ground, and to provide the theoretical and technical supports to the promotion and application of the reinforced soft ground technology with vacuum-surcharge preloading and composite ground.

本项目在已有真空-堆载联合预压竖井地基和复合地基的固结理论基础上，基于“桩-土共同承担上部荷载”和“排水量-体积变化量相等”的原则，以复合地基为研究对象，建立可考虑真空-堆载预压荷载随时间变化、桩体施工对土体的扰动影响、桩体渗透性、初始孔压沿深度变化、桩土体变形、桩体未打穿复合地基和土体非线性固结等因素的各种固结问题计算模型，引入新的求解条件，采用解析解法和数值计算法，系统研究真空-堆载联合预压条件下复合地基固结理论。全面分析这些因素对复合地基固结性状的影响；研究真空-堆载联合预压条件下复合地基固结理论与已有真空-堆载联合预压竖井地基固结理论及复合地基固结理论的特点和差异性；探讨这些理论成果的合理性和适用范围；绘制可供参考使用的固结计算曲线和图表；丰富和发展了真空-堆载联合预压固结理论和复合地基固结理论，为真空-堆载联合预压法和复合地基法共同加固软基技术的推广和应用提供了理论和技术支持。

本项目针对真空-堆载联合预压复合地基固结理论研究方面存在问题和不足，以复合地基为研究对象，在真空-堆载联合预压竖井地基和复合地基已有固结理论研究成果的基础上，考虑工程实践中存在的桩体施工对土体渗透性的扰动、荷载（堆载、真空荷载）施加过程、正（负）压传递规律、桩体未打穿和土体非线性等各种复杂因素的影响，建立考虑各因素影响的固结问题计算模型，采用解析解法，给出了考虑各因素影响的复合地基固结解；通过计算分析和比较研究，探讨了本项目解的正确性和合理性，研究了各因素影响下真空-堆载联合预压复合地基固结规律，绘制出固结度计算曲线图表，促进了真空-堆载联合预压固结理论和复合地基固结理论的丰富和发展。主要研究工作和创新成果如下：.1.给出了分别考虑瞬时荷载、变荷载、忽略土体竖向渗流等情况的真空-堆载联合预压复合地基固结解，进行退化研究，证明了解的正确性和合理性。计算表明：加载速度越快，固结速度就越快；地基应力沿竖向分布形式，对固结有显著影响；真空-堆载联合预压地基比堆载（或真空)预压地基的固结速度快。.2.探讨了真空-堆载联合预压条件下复合地基非线性固结问题，首次给出忽略土体竖向渗流的复合地基非线性固结解，进而给出考虑土体水平向和竖向渗流的复合地基非线性固结解析解。研究显示：土体压缩指数与渗透指数之比越大，固结速率越慢；对于非线性固结，按变形定义的固结度一般比按应力定义的固结度大；初始荷载的大小对固结影响较为明显。.3.推导出考虑土体水平向渗透系数变化的真空-堆载联合预压条件下桩体未打穿复合地基固结解；通过对桩体施工对土体渗透性扰动影响进行简化，即土体渗透系数值为常数，给出了考虑荷载施加过程的真空-堆载联合预压条件下桩体未打穿复合地基固结解。计算分析表明：施工扰动程度和打穿度（贯入比）对复合地基固结有较大影响；扰动越严重，固结越慢；打穿度、桩体刚度和渗透性越大，固结越快。.4.进行了本项目解和已有各解的比较研究。计算结果表明，真空-堆载联合预压条件下，复合地基比竖井地基固结快；对于非线性固结，联合预压比真空预压时地基固结快；真空-堆载联合预压地基比真空预压地基固结快；数值计算的平均固结度比解析解计算的平均固结度偏小，但这种偏差在工程可接受的范围内，本项目解具有一定的工程适用性，可用于地基加固工期要求紧和处理难度高的软粘土地基。