Reliability analyses for soil slopes.

摘要

Several important topics related to soil slope stability analyses were studied, including model development for surficial soil slopes, stochastic influences of hydraulic conductivity on gross and surficial slope stability of embankment dams, influence of rainfall on surficial slope stability, and development of a preliminary dam incident database. To evaluate the surficial factor of safety for soil slopes, a model accounting for influences of the magnitude and direction of groundwater seepage was developed. An equation which describes the effects of hydraulic gradient, shear strength, slope angle, and buoyant unit weight of soil on the minimum factor of safety was derived for cohesionless soil slopes. Computer simulations were used to quantify water movements in soil slopes. A reliability index (β) was employed to characterize the effects of stochastic hydraulic conductivity on slope stability. Stochastic modeling with various standard deviations of log hydraulic conductivity (σ _lnKs) was utilized to investigate the influences of heterogeneity of hydraulic conductivity on slope stability. According to the simulation results, relationships between reliability index and σ _lnKs were established for gross and surficial soil slope stabilities, respectively. The probability of failure increases dramatically with increasing σ_lnKs. Distributions of the factor of safety and reliability index were examined for gross and surficial soil slope stabilities. A comparison of effects of stochastic hydraulic conductivity on gross and surficial slope stabilities showed that heterogeneity of hydraulic conductivity has a greater influence on the surficial factor of safety than on the gross factor of safety, because the former exhibits higher variation than the latter. The effects of spatially-distributed soil hydraulic conductivity on the drawdown, total flux, and hydraulic gradient at the dam downstream face were studied. The coefficients of variation of the drawdown and total flux increase with increasing σ_{ln Ks}. Uncertainties in the drawdown and total flux affect the uncertainty of hydraulic gradient, resulting in higher variations of hydraulic gradient and the surficial factor of safety. Rainfall can increase the water content of soil slopes, leading to a decrease in shear strength, increase in soil weight, and formation of positive pore water pressure. Comparing the effects of these three factors on the surficial factor of safety, the increase in the positive pore water pressure reduces the surficial factor of safety most significantly. A preliminary dam incident database, DamIncDB, was developed to explore the potential of studying slope stability of earth dams using relational data models. The results indicated that earthfill dams consisted of 73% of nearly 5000 dams built in the United States and that the slope sliding and leakage (or seepage) failures comprise approximately of 40% of the total dam incidents, indicating that soil slope stability is an important topic in science and engineering.