| Summary: | 碩士 === 中國科技大學 === 土木與防災應用科技研究所 === 96 === Rainfall infiltration is the mainly factor which caused the unstability of unsaturated slope, durning unsaturated slope stability studies, many research findings of the duration, intensity and rainfall has be approved, but the study of slope stability which caused by the change of soil mechanics induced by rainfall is not enough. At present, durning the studying of slope stability which effected by rainfall, many rainfall condition has been supposed as idealization, and study of the realationship between slope stability and homogeneity rainfall condition. In fact, durning a rainfall process, the water content of soil and the pore pressure which induced by soil moisture has obvious effect for slope forecast and prevention. To aim at the rainfall intensity condition and the stability of slope, use the infiltration theory, saturation-unsaturation theory and shearing-resistance theory. Analyze the feature changing rule of soil moisture and pore pressure in a given water head, based on this study, we can conclude the failure area of slope.
(1)The pore pressure of soil has obviously effect to slope failure and the occure of debris flow, the heterogeneity can affected the infiltration speed. The aim of this sutdy is to analyze the character of soil moisture and pore pressure change when rainfall infiltration in the condition of heterogeneity slope, and to sure the location of the distribution of positive pore pressure. Based on the analyses, we know that the increasing of soil moisture in part area is the main factor which caused the slope unstability.
(2) Based on the van Genuchten and Exponential model, this study uses VSAFT 2 program, a finite element model for variably saturated geological formations, to simulate variations of pore-pressure and soil moisture of heterogeneous unsaturated slope during a constant rate rainfall infiltration.The results can be applied to the analysis of the slop stability to determine the distribution of positive pore pressure which acts an important role in the slop failure events.
(3) At the given pressure head, use the V－G model and EXP model to simulate the rainfall infiltration when q=1cm/hr、q=2cm/hr、q=3cm/hr.As the negative pressure head increasing to zero, the hydrocele occurred in the deepest of soil horizon when Plane Raining; the hydrocele occurred in the grading angle when Slope Raining; the hydrocele occurred in the heterogeneity area when Heterogeneity Slope Raining, where is the place of slope failure.
(4) At the given rainfall intensity, use the V－G model and EXP model to simulate the rainfall infiltration when q=1cm/hr、q=2cm/hr、q=3cm/hr, as the saturation occurred in rainfall infiltration area, the hydrocele occurred in the deepest of soil horizon when Plane Raining; the hydrocele occurred in the grading angle when Slope Raining; the hydrocele occurred in the heterogeneity area when whole Heterogeneity Slope Raining, and the occure of debris blow.
(5)Based on the numerical simunation, analyzed under the situation of Plane、 Slope and Heterogeneity Slope, when q=1cm/hr、q=2cm/hr、q=3cm/hr, analyze the pressure head change with time-varying, and use this result to verify the failure of slope and the occure of debris flow. At last, compare the results of V－G model and EXP model, the results was identical.
(6)Based on the numerical assimulation of 6 observation wells, analyze the relationship of pressure head change character and soil moisture change character with time-varying, and use this to identify the place of slope failure and debris flow occurring. The result show that rainfall infiltration caused positive pore pressure in unsaturated soil and it will increase possibilities of the slope instability and debris flow, the result has its important reference value to parameter chose in engineering.
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