钙质砂地基电解减饱和法抗液化加固机理研究

With the national strategic development of South China Sea, the problem of structures damaged by earthquake or wave effect has drawn more attention. In 1993, an American military base was severely damaged due to the liquefaction of calcareous sand foundation. In recent years, desaturation method, which means to improve the foundation liquefaction strength by reducing the saturation of liquefiable foundation, has become a hot topic of research. However, its mechanism of improving liquefaction resistance and analysis method are rarely seen in report. The project uses direct current to produce little bubbles in soil foundation via electrolysis of water. The physical, electrical, static and dynamic mechanical properties of saturated calcareous sand will be studied by using static and dynamic triaxial tests with electrolysis of sea water. The spatial distribution pattern of bubbles produced by electrolysis of water will be investigated by nuclear magnetic resonance (NMR) test. Full scaled model experiment and shaking table test with capability of pressurization will be done to analyze the liquefaction resistance and pore pressure distribution of saturated calcareous sand foundation under electrolysis of water and to reveal the reinforcement mechanism of the theory. The static and dynamic calculation method of desaturation of calcareous sand foundation will be established based on two-phase flow theory. Combined with coupled dynamic analysis of typical liquefaction examples, the calculation method will be used to evaluate the effect of desaturation method in improving liquefaction resistance. Research results will expand the application of desaturation method in ocean saturated calcareous sand foundation, which is of great importance to seismic prevention and disaster mitigation in the ocean area of our country.

随着我国南海战略开发的推进，海洋钙质砂地基在地震作用下发生液化并导致构造物破坏的问题逐渐引起重视。1993年关岛地震中美军基地就是由于钙质砂地基的液化而导致了严重破坏。近年来，通过减小地基饱和度来提高地基抗液化强度的减饱和法成为土动力学研究的新热点。本项目以直流电解产生气泡的电解减饱和法为技术手段，通过电解静动力三轴和核磁共振试验，分析海水饱和钙质砂试样的物理、电学和静动力学性质，以及饱和度变化的宏微观规律；通过足尺模型试验和可赋压的振动台试验，分析电解作用下钙质砂地基的抗液化强度和孔压变化规律，揭示电解减饱和法的抗液化机理；基于两相流理论，建立钙质砂地基电解减饱和作用的静动力计算方法，并结合典型液化震害实例的数值分析，对电解减饱和法抗液化效果进行评价。研究成果将拓展减饱和法在海洋钙质砂地基中的应用，对我国海洋地区的防震减灾具有重要的参考价值。

减饱和法是通过减小地基饱和度来提高地基抗液化强度的一种砂土地基抗震加固新方法。本项目围绕“钙质砂地基电解减饱和法抗液化加固机理”开展研究，完成的主要工作包括：（1）对钙质砂和同级配石英砂的强度特性进行了对比试验研究，分别探究了单次往返、多次往返和颗粒级配对两者剪切特性和颗粒破碎的影响，并探究了钙质砂与不同界面的剪切接触特性，对海洋钙质砂地基中钢管桩的承载特性进行了研究。（2）基于空心圆柱扭剪试验系统，对钙质砂试样进行不排水单调、循环扭剪试验，分析了有效固结应力、固结应力比对钙质砂静动力特性的影响，并建立了钙质砂归一化耗散能及归一化残余孔压比之间的经验公式。（3）通过小模型试验，研究了电解减饱和法处理钙质砂地基过程中不同电流强度下排水量、饱和度的变化规律及电解过程中的电学特性，并与电解减饱和法处理石英砂地基得到的饱和度规律、电学特性进行对比，研究电解法对不同砂样种类的适应性。（4）采用岩土低场核磁共振（NMR）、医用CT扫描仪设备，对电解过程中试样内部产生的气泡行为进行了观测，探究钙质砂试样内的气泡分布、孔径、迁移规律以及孔隙结构特性。（5）基于两相流模型，分析研究电解减饱和法产生的减饱和区域的扩散规律，验证模型模拟电解减饱和法处理钙质砂地基的可行性，同时研究了电流强度、电极数量、电极厚度、电极倾斜度、电极埋设深度和电极间距等参数对减饱和区域扩散规律的影响。（6）依托深厚砂层的现场条件，进行了现场电解减饱和法的试验研究，验证了电解减饱和法的可行性和经济性。依托本项目发表（含录用）学术论文23篇，其中SCI检索论文7篇，EI检索论文14篇。获得重庆市自然科学一等奖1项（排名：3/6），获得发明专利授权2项，参与制定国家级标准1部、国家军用标准1部。项目负责人入选2019年教育部长江学者（青年学者），项目研究成果拓展了减饱和法在海洋钙质砂地基中的应用，对我国海洋地区的防震减灾具有重要的参考价值。