xli
Abstract
The stability of geotechnical earth structures is often affected if the randomness of geotechnical variables is not incorporated in design. The Factor of Safety (FS) approach holds good only when the input parameters, namely, engineering properties of soil, location of ground water table and loading conditions etc., can be accurately assessed.
The concept of reliability analysis is a well-established mathematical approach to account for these uncertainties of field variables. A few investigations highlighted the sensitivity (S) of random variables on different modes of failure. Also different approaches are available to determine the probability of failure (Pf) for variation of random variables.
Contrarily, design approach incorporating both these effects has not yet been adequately addressed and more rigorous investigation is needed to examine the combined effects of sensitivity of random variables and failure of various earth structures. Also very little is known from the literature regarding any approach to generalize the “partial factor of safety” based upon variations of different geotechnical random variables. In the present study, a correction factor, named as the probabilistic risk factor (Rf) is formulated for different geotechnical random variables based on their variations. These risk factors reflect both reliability and sensitivity of random variables on failure probability, and at the same time may produce an economic design. Pf is calculated by Monte Carlo simulation and sensitivity analysis of each random variable is carried out by F-test analysis. The structure, redesigned by modifying the original random variables with the risk factors, is expected to perform satisfactorily with all the variations of random variables included into it. The proposed approach is applied to five different earth retaining structures viz. cantilever retaining wall, gravity retaining wall, reinforced retaining wall, sheet pile walls and finite slopes. The gravity retaining wall is analysed for static, pseudo-static and pseudo-dynamic conditions in a probabilistic framework. It is observed that if the variation in some properties, like internal angle of friction and cohesion of soil be properly identified, significant reduction in cost can be achieved. The study also proposes various design charts for different geotechnical earth structures, under both static and dynamic loading conditions, for different variations of random variables, based upon the proposed design approach.This may help to simplify the use of the proposed method for the practicing engineers.
Keywords: Geotechnical Random Variables, Reliability Analysis, Probability of Failure, Sensitivity Analysis, Earth Structures, Risk Factors
