真空—堆载联合预压下塑料排水板地基的侧向变形机理与预测方法研究

Prefabricated vertical drains (PVD) with the combination of vacuum pressure and surcharge loads has been widely utilized for improving soft ground, however, studies on the ground lateral deformation as well as its detrimental effects to surrounding foundations are quite limited. This research program focuses on the lateral deformation of PVD-improved ground and plans to conduct the following research work. (1) A triaxial test device that would apply both vacuum pressure and vertical loads will be developed, and a series of triaxial tests of soil specimens with mini-PVD inserted at the center are planned to be conducted using this newly developed device; based on the tests, it would be explored the variations regularities of the stress ratio (K) of the soil specimen under different confining stress, vacuum pressure, vertical load and loading rate. (2) Large scale laboratory model tests of PVD-improved ground under combined vacuum pressure and surcharge loads will be conducted, and the layered settlement, lateral deformation and pore water pressure behavior of the PVD-improved ground would be explored; (3) 3D finite element model of PVD-improved ground will be established and be verified by comparing with the model test results; then numerical simulations under different conditions will be performed to analyze the variation regularities and influence area of the lateral deformation of PVD-improved ground under combined vacuum pressure and surcharge loads. (4) Combining the tests and numerical studies, the lateral deformation mechanism of PVD improved ground under the combination of vacuum pressure and surcharge loads would be revealed; and a simple method will be proposed to predict the lateral deformation of PVD-improved ground under the combined loads condition. These research achievements can provide a new scientific basis for improving the design theory of PVD-improved ground under combined vacuum pressure and surcharge loads.

塑料排水板（PVD）结合真空—堆载联合预压法广泛用于软土地基的处理，但现阶段对其侧向变形及可能对邻近既有地基基础造成的不利作用研究甚少。本项目重点针对PVD软基的侧向变形，开展如下研究：（1）研制能同时施加轴压和真空压力的三轴压缩试验装置，制备内含mini-PVD的土样，开展其真空—轴压共同作用下的三轴试验，系统研究不同围压、真空压力、轴压及加载速率下其应力比K的变化规律；（2）开展设置有多条PVD的大比例软基真空—堆载联合预压模型试验，测试不同真空压力、堆载和加载速率下PVD地基的分层沉降、侧向变形和孔压等；（3）建立PVD地基的三维有限元模型，并基于模型试验进行校核和完善，进而开展多工况仿真计算，系统研究真空—堆载联合预压下PVD地基侧向变形的主要影响因素、变化规律和影响范围；（4）综合上述试验和数值分析，揭示真空—堆载联合预压下PVD地基的侧向变形机理，并提出其侧向变形预测计算方法。

目前针对真空—堆载联合预压塑料排水板（PVD）地基侧向变形的研究甚少，致使现阶段对其侧向变形的机理认识不清楚，工程实际中仍不乏联合预压下PVD地基由于侧向变形过大对周围环境、地基基础以及地下管线造成挤压或破坏的案例。本项目针对这一关键问题，从实验、仿真、理论分析三个层面全面探索了真空—堆载联合预压下PVD地基的侧向变形特性，完成的主要研究内容及获得的主要成果如下：（1）采用大比例模型试验和数值仿真相结合的方法，阐明了真空—堆载联合预压下PVD地基侧向变形的主要影响因素（真空压力、堆载、堆载速率等）、变化规律和影响范围；（2）研制了可同时施加真空压力和轴向压力的三轴压缩试验装置，并开展了系列三轴压缩试验和有限元仿真分析，从变形比的角度系统阐释了内含mini-PVD土体竖向和水平向应变随各主要影响因素的发展趋势和变化规律；（3）结合试验、仿真成果和理论分析系统研究了真空—堆载联合作用下PVD地基土的应力状态（应力比Ke）随真空压力、堆载、堆载速率和先期真空压力固结时间的变化规律，揭示了PVD地基土的侧向变形机理；（4）基于上述系列成果和理论分析提出了真空—堆载联合预压下PVD地基侧向变形模式的判别方法及侧向变形的预测计算方法，并构建了便于工程应用的计算图表。本项目针对PVD地基侧向变形这一非常关键的问题开展研究，系列研究成果为完善真空—堆载联合预压软土地基的设计理论提供了科学依据和新的思路，是对软土地区工程分析理论的创新；所提出的侧向变形预测方法对指导具体工程实践，特别在我国人口稠密的沿海地区、河口地区及湖泊区域内诸多基础设施工程的设计和建设中具有重要的指导意义和应用价值。