Development of novel ground improvement technique of soil desaturating by air injection

防止地震引起的土壤液化对减轻液化危害具有重要意义。然而，目前可用的技术的执行成本通常是昂贵的。注气技术是一种简单、廉价的替代方法，它通过注入加压气泡使饱和土去饱和，从而提高液化强度和降低液化敏感性。本项目旨在研究开发注气去饱和土液化对策新技术所必需的割草项目。（1）从理论上推导了部分饱和砂土抗液化强度的影响因素，并通过一系列的三轴试验研究了这些因素的影响。结果表明，饱和度对液化抗力有显著影响。抗液化强度还取决于初始围压， ...更多信息 初始孔隙压力;围压越高，初始孔压越低，部分饱和砂土的抗液化强度越高。研究发现，抗液化比与潜在体积应变之间存在着独特的关系，这使得在考虑这三个因素影响的情况下，可以估算部分饱和砂土的抗液化强度。(2)A摘要通过离心试验研究了饱和土-结构体系的抗震性能及液化对策措施--饱和土-结构体系的液化效果。结果表明，半饱和砂土上的结构沉降远小于饱和砂土上的结构沉降。(3)A通过一系列的模型试验，利用空气注入探头模拟空气注入饱和土壤，研究了空气注入过程中土壤的减饱和机理。结果表明，土壤的垂直渗透率、水平渗透率以及注入空气压力对减饱和的演化有很强的控制作用。使用多相流模拟器进行数值分析，以描述从测量得到的土壤去饱和的演变，并检查该模型作为预测工具，使去饱和的演变在原位随时间和空间的适用性。预测显示出良好的协议与测量的速率，幅度，饱和度的分布，和气流速率。少

Measures preventing earthquake-induced soil liquefaction are of significant importance to mitigate the liquefaction hazards. However, execution costs of currently available technique are generically expensive. An air-injection technique may be a simple, inexpensive alternative-this leads the saturated soils to the desaturated by injecting pressurized air bubbles, resulting in a higher liquefaction strength and the lower susceptibility This project aims at investigate Mowing items which are essential to develop a novel liquefaction countermeasure technique of soil desaturation by air injection.(1)Influential factors of the liquefaction resistance of partially saturated sand are derived from theoretical consideration and effects of the factors are examined through a series of triaxial tests. It was confirmed that the degree of saturation has a significant effect on the liquefaction resistance. It also appeared that the liquefaction resistance depends on the initial confining pressure and … More the initial pore pressure; the higher the confining pressure and the lower the initial pore pressure, the higher the liquefaction resistance of partially saturated sand. A unique relationship between liquefaction resistance ratios and the potential volumetric strain was found, which enable to estimate the liquefaction resistance of partially saturated sand with the effects of the three factors taken into account.(2)A series of centrifuge tests was conducted to investigate seismic behavior of desaturated soil-structure system and effects of desaturation as a liquefaction countermeasure technique. It was confirmed that settlements of the structure on partially saturated sand is much smaller than that of the saturated sand.(3)A series of model tests that simulate air injection into saturated soils using air-injection probes, was conducted to investigate the desaturation mechanism during air injection It was found that the evolution of desaturation is strongly controlled by the vertical and horizontal permeabilities of the soil as well as the injection air pressure. The numerical analyses using a multiphase flow simulator is conducted to describe the evolution of the soil desaturation obtained from the measurements, and to examine the applicability of the model as a prediction tool enabling the evolution of desaturation in situ to be followed with time and space. Predictions show a good agreement with the measurements regarding the rates, magnitudes, distribution of degree of saturation, and airflow rates. Less