Reliability assessment of test embankments on soft Bangkok clay by variance reduction and nearest-neighbor methods

Abstract

This paper presents the application of probabilistic slope stability model based on variance reduction method on the Nong Ngoo Hao (NNH) test embankment and the probabilistic settlement evaluation of AIT test embankment using the nearest-neighbor method. The NNH embankment was constructed to failure. Sample autocorrelations were obtained from corrected vane shear test data as well as from the Dutch cone test data in both horizontal and vertical directions. The results showed that using a design criteria of probability of failure of 10 −3, a design safety factor of 1.12 is recommended for 3-D analysis. In 2-D analysis, the variance reduction method yielded lower probabilities of failure compared to an earlier work based on Monte Carlo method. For the AIT test embankment, the statistical data for the occurrence of fine sand and silt lenses in the soft Bangkok clay were obtained and the inclusions were probabilistic settlement prediction in conjunction with the method of Skempton and Bjerrum and Lacasse's approximation showed reasonable agreement with the observed values.