Effect of spatial variability on probability-based design of excavations against basal-heave

This paper examines the effect of spatial soil variability, modeled as a twodimensional (2-D) random field, on the computed probability of basal-heave failure in a braced excavation in clay. The random field modeling (RFM) of clay is realized using a framework that combines Cholesky decomposition method and Monte Carlo simulation (MCS). Considering that the horizontal and vertical scales of fluctuation are generally unequal for clay, various combinations of the horizontal and vertical scales of fluctuation are examined within this framework. The effect of 2-D RFM of undrained shear strength of clay in a braced excavation is demonstrated with a case study that focuses on a simple probability-based design. The results show that negligence of the 2-D spatial random effect could yield a basal-heave design that is unduly over-conservative: at an acceptable or target failure probability level, the required factor of safety in a limit equilibrium analysis is unreasonably high.