Applicability of chemical grouting for the improvement of liquefaction susceptibility of saturated sandy deposits

经化学灌浆处理的砂质沉积物在强震中表现出良好的抗液化能力，这是众所周知的。导致抵抗行为的基本机制至今仍不清楚。为了深入了解其机制，本研究项目进行了多项实验工作。特别是，详细研究了低含量二氧化硅处理的抗液化能力的提高，从而以合理的成本改善砂质沉积物。化学注浆在砂土改良工程中的应用，需要对注浆的分布和强度进行数值分析。为了正确地分析这一问题，需要考虑到剪胀效应和强度增加效应的性能良好的本构模型。在化学灌浆的基础上，采用水泥浆作为替代材料，提高了混凝土的抗液化能力。通过本研究获得的主要结果可以总结如下：1。循环三轴试验对试样进行了不同的二氧化硅含量。当掺量大于3%时，试件的剪胀率变化呈膨胀趋势，认为这是导致其抗液化行为的原因；当掺量小于3%时，初始液化（孔隙水压力达到初始有效围压）后，剪切变形略有增加，但强度和剪胀特性差异不大，降低了完全（突变）液化的可能性。这一事实可能说明，低硅含量处理试样的低水力导率使试样不会出现灾难性的液化破坏，这在一定程度上得到了速砂试验的支持，速砂试验结果表明，处理后的砂具有较高的抗速砂能力，并且需要较长的时间才能发生最终破坏。在化学灌浆的基础上，将具有较高强度的水泥浆体作为改善砂层的材料。对于高粘度液体的注射，改变注射速度的方法是有效的。为了了解硅粉和水泥处理砂的整体力学行为，采用均质化技术在细观力学行为和宏观力学行为之间架起桥梁。将这种方法应用于复杂材料还需要更多的研究。严重的液化破坏是在强震期间和强震后随着砂质沉积物的流动而发生的。本构模型是为了考虑砂土密度变化的影响而建立的，并应用于孔隙水运动引起的流动问题。这些结果在研究报告（日语）中得到了充分的讨论。少

The fact that sandy deposits treated by chemical grouting show good resistance to liquefaction during strong earthquakes is well known. The fundamental mechanisms leading to resistant behavior remain unknown up to the present time. In order to get insight into the mechanisms, several experimental works have been performed in this research project. In particular, the increase of resistance to liquefaction treated by a low-content silica was investigated in detail, which leads to the improvement of sandy deposits with reasonable costs. The application of chemical grouting for the purpose of the improvement of sandy deposits to practice requires the numerical analyses on the distribution of grouting and strength. For the proper analysis of the problem requires the well behaved constitutive model with account for the effect of dilatancy and increase of strength. In addition to chemical grouting, cement paste was used as an alternative material leading to the increase of the resistance to l … More iquefaction. The main results obtained through this study can be summarized as follows :1.Cyclic triaxial tests were performed on the specimen with varying the contents of silica. The specimens with the contents more than 3% show the change in dilatancy with the tendency of expansion, which is believed to result in the resistant behavior to liquefaction;2.The specimens with the content less than 3% show little difference in strength and dilatancy behavior, although shear deformation shows a little increase after initial liquefaction (pore water pressure reaches to the initial effective confining pressure), which reduces the possibility of complete (catastrophic) liquefaction. This fact may indicate the fact that low hydraulic conductivity of treated specimen with low content of silica prevents the specimen from showing catastrophic liquefaction failure, which is partly supported by the quick sand test with the result that the treated sand shows high resistance to quick sand and needs a long duration until final failure occurs.3.In addition to chemical grouting, the cement paste which leads to the higher strength were used as a material for improving sand deposits. For the purpose of injecting the liquid with high viscosity, the method with varying the injection speed was found effective.4.To understand the overall mechanical behavior of treated sand with silica and cement, the homogenization technique was applied to bridge the micromechanical behavior and macroscopic behavior. More study is required to apply the method to the complex material.5.The severe damages due to liquefaction are believed to occur with the flow of sandy deposits during and after strong earthquake excitation. The constitutive model was developed in order to account for the effects of change in density of sand and was applied to the problem of flow due to the movement of pore water.These results were fully discussed in the research report (in Japanese). Less