PROBABILISTIC APPROACH TO PREDICTION OF CONSOLIDATION SETTLEMENT

The method of derived distributions is used to develop a probabilistic model for predicting the total settlement in a compressible clay layer in terms of uncertain soil compressibility and loads. The settlement ratio (total settlement divided by thickness of compressible layer) is a function of two independent random variables (compressibility factor and load factor). The compressibility factor is a function of two dependent random variables (compression index and initial void ratio), and the load factor is a function of two independent random variables (total stress at the midheight layer and the preconsolidation stress). The compressibility factor can be described by a normal distribution, and the load factor by a log-normal distribution. The derived distribution of the settlement ratio is also well approximated by a log-normal distribution that approaches a normal distribution as the number of soil samples taken for the settlement prediction increases. Graphs are developed to estimate the settlement ratio parameters in terms of the average dry density of the soil. The effect of the number of samples and the vertical and horizontal correlation on the density function of the settlement ratio is also evaluated.