| Budget Amount *help |
¥2,800,000 (Direct Cost: ¥2,800,000)
Fiscal Year 2006: ¥900,000 (Direct Cost: ¥900,000)
Fiscal Year 2005: ¥1,900,000 (Direct Cost: ¥1,900,000)
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| Research Abstract |
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
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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
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