FUNDAMENTAL STUDY ON THE MITIGATION OF LIQUEFACTION INDUCED DISASTER BY INJECTING AIR BUBLLES IN THE GROUND

通过一系列室内试验，研究了桑迪的颗粒大小、圆度、相对密度和孔隙水中气泡对饱和度（Sr）与纵波速度（V_p）关系的影响。通过原状土样和重塑土样，研究了饱和度对砂土液化强度的影响。利用模型砂土地基研究了气泡的产生方法和气泡的插入方法，得出以下结论：（1）与砂土颗粒大小对B值-Vp关系的影响不同，砂土颗粒大小对Sr-Vp关系的影响较小。在饱和度为90%~ 100%的范围内，P波速度随饱和度的增加而迅速增加，相对密度对Sr-V_p关系的影响很小，孔隙水中气泡的存在对B值-V_p关系和Sr-V_p关系的影响都很大，而孔隙水中气泡的存在对Sr-V_p关系的影响很小。（4）通过对不排水循环三轴试验所得液化强度的比较，认为向桑迪中注入气泡降低饱和度的方法是一种有效的减轻砂土液化灾害的方法。(5)在模型试验的基础上，成功地提出了在一定水头下向砂土中注入气泡溶解水的简易加固方法。

A series of laboratory tests were performed in order to investigate the effects of the size and the roundness of soil particles, relative density, and air bubbles involved in the pore water of sandy soils on the relationship between the degree of saturation (Sr) and the P-wave velocity (V_p). The effect of degree of saturation on the liquefaction strength of sand was studied both on the undisturbed and reconstituted samples. The methods to generate air bubble and to insert the air bubble into the ground were also studied using model sand ground.Following were concluded : (1) Unlike the effect of the size of soil particles of sand on the B-value-V_p relationship, its effect on the Sr-V_p relationship is small. The P-wave velocity increases rapidly with increasing degree of saturation from 90 % to 100 % for all sands tested ; (2) The effects of relative density on the Sr-V_p relationship are negligible ; (3) The effects of air bubbles involved in pore water both on B-value-V_p relationship and Sr-V_p relationship are significant ; (4) By comparing the liquefaction strengths obtained in the undrained cyclic triaxial tests on Futtsu sand, the method to decrease the degree of saturation by injecting the air bubbles into the sandy ground is expected to be a useful method to decrease the disasters induced by the sand liquefaction. (5) A simple method to unsaturate sand ground was successfully performed based on model ground test by inserting air bubble dissolved water into the ground under some water head.