Effect of spatial variability on the slope stability using Random Field Numerical Limit Analyses

This paper presents a probabilistic approach to evaluating the geotechnical stability problem by incorporating the stochastic spatial variability of soil property within the numerical limit analyses (NLAs). The undrained shear strength and unit weight of soil are treated as a random field which is characterized by a log-normal distribution and a spatial correlation length. The current calculations use a Cholesky Decomposition technique to incorporate these random properties in NLAs. The Random Field Numerical Limit Analyses are applied to evaluate the effects of spatial variability of soil property on the slope stability and failure mechanism of slope. Monte Carlo iterations are then used to interpret the slope reliability and the dimension for collapsed slope for selected ranges of the coefficient of variation in soil property and the ratio of correlation length to slope height. Finally, the variation in the dimension of collapsed slope is examined in terms of the variability of slope reliability.Japan Society for the Promotion of Science (KAKENHI Grant 25289149

Bearing Capacity of Spatially Random Cohesive Soil Using Numerical Limit Analyses

This paper describes a probabilistic study of the two dimensional bearing capacity of a vertically loaded strip footing on spatially random, cohesive soil using Numerical Limit Analyses (NLA‐CD). The analyses uses a Cholesky Decomposition (CD) technique with mid‐point discretization to represent the spatial variation in undrained shear strength within finite element meshes for both upper and lower bound analyses, and assumes an isotropic correlation length. Monte Carlo simulations are then used to interpret the bearing capacity for selected ranges of the coefficient of variation in undrained shear strength and the ratio of correlation length to footing width. The results are compared directly with data from a very similar study by Griffiths et al. in which bearing capacity realizations were computed using a method of Local Average Subdivision (LAS) in a conventional displacement‐based Finite Element Method (FEM‐LAS). These comparisons show the same qualitative features, but suggest that the published FEM calculations tend to overestimate the probability of failure at large correlation lengths. The NLA method offers a more convenient and computationally efficient approach for evaluating effects of variability in soil strength properties in geotechnical stability calculations

総費用最小化理論に基づく液状化対策地盤の最適地盤改良度の提案

1 はじめに / ２ 液状化リスク分析手法 / ３ 地盤改良における割増係数 / 4 液状化リスク分析結果 / 5 最適地盤改良度の提案 / ６ 結論第7回構造物の安全性・信頼性に関する国内シンポジウムThe Seventh Japan Conference on Structural Safety and ReliabilityThis paper presents a liquefaction risk analysis in terms of the percent defective in ground improvement. In this paper, the liquefaction potential of artificially solidified ground is analyzed statistically using Monte Carlo Simulation of the nonlinear earthquake response analysis considering the spatial variability of soil properties. Damage cost induced by a partial liquefaction in the solidified ground is estimated based on the reduction of the seismic bearing capacity obtained by random field numerical limit analysis. The annual liquefaction risk is calculated by multiplying the liquefaction potential with the damage costs caused by a partial liquefaction. Effects of percent defective in ground improvement on the liquefaction risk of anti-liquefaction ground investigated using the hazard curve, fragility curve induced by liquefaction, and liquefaction risk curve. Moreover, the percent defective in ground improvement was discussed from the viewpoint of the quality verification for the construction of anti-liquefaction ground. Finally, Finally, ideal strength of ground improvement was decided based on minimization of expected total cost