Research for the Evaluation of Strength of Unsaturated Soil under Seepage Water Accompanied by Volume Change

非饱和土体的强度是评估斜坡和/或河堤稳定性所必需的。在本研究中，第一项是测量粉土在渗水作用下发生坍塌时的孔压。其次，由于粉土中的孔压很小，所以用总压力而不是有效压力来比较定压和定容的抗剪强度。主要研究成果如下：(1)在土层模型试验中，测得的孔压相当于渗水作用下土层发生坍塌时的上覆岩层压力。在改进的固结仪试验中，由于渗流很难在不释放孔隙空气的情况下进入土体孔隙，测得的孔压相当于覆盖层压力的1/30。(2)利用直剪仪和环剪仪，对两个粉土试件进行了…试验，其中非淹没试件和非淹没土峰值强度的60%剪应力水平的浸没试件。结果表明：(1)试件浸水坍塌后，剪应力降至零，但随应变的增加略有恢复；(2)浸水后阻力角为20.4°时，浸没后恢复的强度为27.1°。(3)在松散试件的定容试验中，封闭土中的平均压力下降较大，剪应力变小。然而，在松散试件的定容试验中，当浸没阻力角为20.4°时，浸没和恢复强度仅为27.1°。强度参数特别是阻力角变得与非浸水试件在恒压作用下的抗剪强度相当。(4)抗剪强度很大程度上取决于内应力和体积变化。(3)针对上述结果未能建立边坡变形和稳定性分析的数值模拟，并希望下一步的评论成为现实。(1)渗水作用下，塌方不是发生在密实粉土中，而是发生在疏松粉土中，而松散粉土容易发生塌陷。(2)恒定体积试验是可以推荐的，因为它跟踪水下内应力的变化，而且是恒定压力。较少

Necessary is the strength of unsaturated soils for the stability evaluation of slopes and/or river levees. In this study, first item is to measure the pore pressure occurred with collapse under seepage water in silt. Second is to compare the shear strength obtained from constant pressure with the one from constant volume, using not effective pressure but total pressure, because pore pressure is very small in silt. Obtained results are following.(1)In soil layer model experiment, the pore pressure is measured equivalent to the overburden pressure when collapse occurred in soil layer under seepage water. In modified Oedmeter test, measured pore pressure is fairly the amount of 1/30 of overburden pressure owing to the difficulties that seepage does not enter soil pore without pore air released.(2)Using the direct shear and ring shear apparatus, two specimens of silt with "the non-submerged one" and "the submerged at the 60% level shear stress of the peak strength of non-submerged", are te … More sted both by constant pressure and constant volume, as is obtained following results.(1)Just after specimen submerged and collapsed, the shear stress falls down to zero but recovered a little with strain increment.(2)The submerged and recovered strength as angle of resistance 20.4° is smaller than the non-submerged one as 27.1°.(3)In constant volume test of loose specimen, average pressure in confined soil falls greatly and then shear stress become small.However, strength parameter especially angle of resistance become equal to the one of non-submerged sample corresponding to constant pressure.(4)It is necessary that the shear strength greatly depends on both inner stresses and volume change.(3) It is failed to establish the numerical simulation of slope deformation and stability analysis which aims to examine the above results, and then next comments are hoped to become true.(1)The collapse occurs not in dense silt but loose silt under seeped water, and the latter soil is easy to collapse.(2)The constant volume test can be recommended because it follows inner stress change under water, and the constant pressure. Less