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

非饱和土的强度对于边坡和/或河堤的稳定性评价是必要的。在本研究中，第一项是测量淤泥中渗流水作用下崩塌时产生的孔隙压力。二是比较定压法与定容法的抗剪强度，不使用有效压力，而使用总压力，因为粉土孔隙压力很小。得到的结果如下：(1)在土层模型试验中，测得的孔隙压力相当于渗水作用下土层发生崩塌时的覆盖层压力。在修正Oedmeter试验中，由于孔隙空气不释放，渗流难以进入土壤孔隙，因此测得的孔隙压力大致为覆盖层压力的1/30。(2)采用直剪和环剪试验装置，对“未被淹没”和“处于未被淹没峰值强度60%剪切应力水平下”的2个粉土试件进行了恒压和恒容试验，得到如下结果：(1)试样刚淹没崩塌后，剪应力降至零，但随着应变的增加，剪应力略有恢复。(2)当阻力角为20.4°时，淹没和恢复强度小于未淹没时的27.1°。(3)在松散试样等体积试验中，承压土的平均压力大幅下降，剪应力变小。而在恒压条件下，强度参数尤其是阻力角与未浸没试样的强度参数趋于一致。(4)抗剪强度对内应力和体积变化都有很大的依赖。(3)未能建立旨在检验上述结果的边坡变形与稳定分析的数值模拟，希望后续评论能够实现。(1)塌方不发生在密实粉土中，而发生在渗水作用下的松散粉土中，后者易发生塌方。(2)恒容试验遵循水下内应力变化规律，且压力恒定，因此推荐采用恒容试验。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