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Slope Stability Analysis of Engineerning Spoil Accumulation Based on the Unsaturated Soil Mechanics Theory

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Tutor: TangHongMei ChenHongKai
School: Chongqing Jiaotong University
Course: Hydraulic Structure Engineering
Keywords: Three Gorges Reservoir,Extreme rainfall,Engineering spoil,Unsaturated soil,Fixed
Type: Master's thesis
Year:  2011
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In recent years, with the frequent occurrence of extreme weather conditions, the survival of mankind formed a severe test, people formed under extreme weather conditions, geological disasters gradually pay attention to it. Since the construction of the Three Gorges Reservoir, the reservoir population of about 110.56 million migrant relocation, relocation or partial removal of the whole county (city) level urban 13, 116 township-level town, library district resettlement area 15000km2. Relocation process produces a large number of works spoil, spoil, is dumped directly on the slope above, and in extreme weather conditions, these works may spoil landslide accumulation body, relocation of residents on the lives and property caused by affected. Therefore, the project spoil heap landslides in response to extreme weather conditions Mechanism become an important topic. This paper analyzes the results of previous studies, based on a pilot study, theoretical analysis and numerical simulation of combining research methods, Chongqing Three Gorges Project spoil heap of a body as an example, analyzed the effect of extreme rainfall, engineering abandoned infiltration of soil accumulation slope lines, pore water pressure and infiltration depth with the rainfall intensity, rainfall duration and change in void ratio relationship; then were corrected and uncorrected through the stability calculation, the body side of the project spoil heap slope different void ratio, different rainfall conditions stability calculation, the void ratio obtained under different projects in different spoil deposit slope under rainfall transient stability factor; final calculation formula of the two results were compared analysis. The main research contents and results are as follows: (1) analysis of the latest research situation at home and abroad, and the Three Gorges Project spoil particles curve, natural bulk density, shear strength parameters and soil water characteristic curve analysis of the nature of a pilot study parameters that This class works fine grained soil containing gravel spoil; reservoir engineering spoil saturated hydraulic conductivity with void ratio increases, generally shows an increasing trend. Saturated hydraulic conductivity in the pore ratio is less than 0.7, the increasing trend with moderate void ratio, on the contrary, saturated hydraulic conductivity increases with the void ratio increases rapidly; saturation below 60%, the soil cohesion With the increase of saturation; saturation greater than 60% after the soil cohesion with increasing saturation decreases rapidly; soil internal friction angle? value varies with soil saturation from 20 % increases, showing a decrease slowly over 40% saturation, and then decreases rapidly rendered, greater than 60% saturation, and tends to decrease slowly after saturation greater than 80%, and showed a trend decreases rapidly ; the same degree of saturation, with the soil matric suction void ratio decreases with an increase in the same void ratio, the matric suction as saturation increases. After saturation of 80%, the size of the suction effect is no longer subject to density, porosity greater than 0.7081, the soil water characteristic curve with saturation did not change significantly. (2) the use of unsaturated soil strength theory, considering soil matric suction on the Swedish arc method of calculation was modified to make it suitable for both saturated and unsaturated soil slope slope stability calculations. (3) According to the Three Gorges Reservoir largest extreme rainfall events over the years, assuming continuous engineering experience accumulation slope spoil antecedent rainfall (25mm / d) 4 Heaven and extreme rainfall (100mm / d, 200mm / d, 300mm / d) 2 Ììusing GEOSTUDIO (2004) software to calculate the given boundary conditions of unsaturated works spoil deposit slope seepage within the process to obtain the various moments pore water pressure inside the slope distribution. The numerical results show that: the effect of extreme rainfall on pore water pressure had a significant effect of several parameters: extreme rainfall intensity and the relationship between permeability coefficient, rainfall duration. The same as in the early rainfall, rainfall duration is consistent, extreme rainfall intensity and greater permeability, the greater the depth of rainfall infiltration on slope pore water pressure within the larger sphere of influence. Engineering spoil heap at the foot of the slope Slope pore water pressure at the waist than the slope with the slope of the shoulder is more intense, the most obvious influence by extreme rainfall. (4) Depending on the time each node values ??of water content and pore water pressure, the use of the specification of the Swedish arc method and the modified method were Swedish arc stability factor for each time were calculated results show that: Correction Formula stability after more traditional formula to calculate the overall stability has increased, increase the range of 0.245-0.293. Unsaturated slope soil porosity ratio of 0.7081 when: a) the uncorrected formula, extreme rainfall ¢ñ for 45.6 hours later, engineering spoil deposit slope stability factor is less than 1; corrected formula, extreme rainfall ¢ñ under extreme After 48 hours, rainfall, engineering spoil deposit slope stability factor of 1.062. 2) uncorrected formula, extreme rainfall ¢ò for 40.3 hours later, engineering spoil deposit slope stability factor is less than 1; corrected formula, extreme After 48 hours, rainfall, stability factor dropped to 1.023, engineering spoil deposit slope stability in the critical state. 3) uncorrected formula, extreme rainfall ¢ó effect 36 hours after the project spoil deposit slope stability factor is less than 1; corrected formula, corrected time from 36 hours to 44.5 hours, the time increased by 8.5 hours, making unsaturated slope soil matric suction fully play its role, the results closer to the actual situation.
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