RELIABILITY BASED ANALYSIS OF BEARING CAPACITY OF FOOTINGS ON REPLACED SOIL

Abstract

Geotechnical engineering designs depend on soil parameters and theoretical formulas which lead to inaccurate results. The lack of accuracy is covered by the factor of safety. The complementary solution is the reliability analysis which gives an index to choose the proper factor of safety to make the design safer and more economic. In this study, a procedure for carrying out reliability analysis of bearing capacity of foundation resting on soil improved by soil replacement with different dimensions of replacement (8 models) is described. The procedure requires definition of standard deviation of the undrained shear strength, angle of internal friction and the unit weight of the stone material and the surrounding soil. The procedure is an extension of the point estimate method in which the expected values of the standard deviation of the capacity and demand functions are calculated. The probability of failure, the reliability, central factor of safety and reliability index are calculated as appropriate. It was concluded The reliability and the probability of failure depend mainly on the approach used in the estimation of bearing capacity, a number of equations were derived in the literature to estimate the bearing capacity but the degree of conservation for each one is different from one to another. In some cases analysed in this study, the probability of failure was found to be less than 1% depending on the value of reliability index obtained from reliability tables which are always greater than 2.2 based on standard normal distribution.