分级真空预压加固高粘性吹填土微观结构时效特性与固结模型研究

Vacuum preloading is a soft ground improvement method that has been widely used by geotechnical engineers and specialists to accelerate the rate of consolidation. But there also exists reinforcing failure phenomenon when dealing with high clayed dredger fill. The reason is fine particles will gather around and plugging of vertical drains under the action of a powerful vacuum pressure. So we had proposed a new method of step vacuum preloading to reinforce high clayed dredger fill and the good reinforcement effect had been obtained. But the mechanism study need to be further strengthened. Therefore, this study is based on micro mechanism research, analysis the time effect of microstructure for high clayed dredger fill consolidated by step vacuum preloading, investigate the formation process of microstructure of dredger fill in consolidation process, obtain he relationship between microstructure variation and time. Combine the macro physical and mechanical performance and microstructure variation to reveal the consolidation mechanism of high clayed dredger fill by step vacuum preloading. Establish consolidation model based on time effect of microstructure of dredger fill, and confirm the feasibility of step vacuum preloading to reinforce high clayed dredger fill.

真空预压法作为一种较为成熟的软土地基加固技术已广泛应用于沿海地区围海造陆工程实践，取得了较好的经济效益。但是当对于新近吹填的、粘粒含量较高的吹填土进行加固时，也存在着加固失败的现象。经过对失败原因进行深入分析发现，高粘性吹填土中的大量细颗粒会在强大的真空吸力作用下聚集到排水体四周，严重堵塞排水体，使得排水体失效，导致加固失败。由此，申请人所在的课题组提出了利用分级真空预压法来加固高粘性吹填土的新方法，并取得了较好的加固效果，但机理研究有待进一步加强。因此，本项目从机制学的角度出发，开展分级真空预压法加固高粘性吹填土微结构时效特性研究，探讨分级真空预压下吹填土微观结构的形成过程，确定微结构变化与时间的关系，结合宏观物理力学表现与微结构变化揭示分级真空预压法加固高粘性吹填土的固结机理，建立考虑吹填土微结构时效特性的固结变形本构模型，从机制学角度证实分级真空预压法加固高粘性吹填土的可行性。

针对传统真空预压法加固新近吹填的高粘性吹填土存在细颗粒堵塞排水体、加固失败的现象。课题组提出了分级真空预压法加固高粘性吹填土的方法，并通过室内试验验证了其有效性。本项目在前期研究的基础上，开展分级真空预压法加固高粘性吹填土的微观机理研究，深入研究吹填土加固过程中结构形成的时效特征，从机制学角度证实分级真空预压方法加固高粘性吹填土地基的可行性。.利用自制模型箱开展了分级真空预压法加固高粘性吹填土室内模拟试验，监测了吹填土固结过程中沉降量、排水量、孔隙水压力随时间的变化规律。从含水率、孔隙溶液浓度、粘粒含量、渗透系数几个方面出发，建立了吹填土宏观性质与时间的关系。利用自行研制的冷冻取样器获取各级荷载下的吹填土微观结构试样，运用扫描电子显微镜（SEM）和压汞仪微观试验技术，进行微观结构性质测试，探讨了固结过程中吹填土微观结构特征、孔隙率、平均孔径、孔径区间分布及孔隙分形维数等微结构参数变化的时间效应。充分考虑土体微观结构的时间效应，建立了固结过程中宏观性质和微观结构参数之间的关系，联合宏观物理力学特征和微观结构变化共同揭示了分级真空预压加固高粘性吹填土的固结机理，对推广分级真空预压法加固高粘性吹填土地基处理技术具有重要的理论意义。