Determination of soil property characteristic values from standard penetration tests

Characteristic values of soil property is a key element in geotechnical design guidelines, particularly for probability-based design codes, and it is usually defined as a pre-specified quantile, such as a lower 5% quantile in Eurocode 7, of the probability distribution of soil property. Such a probabilistic characterization requires a large number of data points from laboratory and/or in situ tests, which are usually not available for most geotechnical projects, especially for those with medium or small sizes. For most projects, only a limited number of standard penetration test (SPT) N values are generally available. It is therefore rather challenging to determine the probability distribution and characteristic values for geotechnical design. To address this challenge, this paper presents a Bayesian equivalent sample approach that determines the probability distribution and characteristic value of effective friction angle and Young's modulus using only a limited number of SPT N values. Two case histories are used to illustrate the approach.