Decoupled reliability-based geotechnical design of deep excavations of soil with spatial variability

•General decoupled method for reliability-based geotechnical design.•The method is robust to model complexity and parameter dimension.•Non-parametric and global estimation of failure probability functions.•Case study on the design optimization of deep excavation in Singapore marine clay.•Effects of statistical characteristics of soil properties on design is investigated. This paper presents a general decoupled method for reliability-based geotechnical design that takes into account the spatial variability of soil properties. In this method, reliability analyses that require a lot of computational resources are decoupled from the optimization procedure by approximating the failure probability function globally. Failure samples are iteratively generated over the entire design space so that their global distribution information can be extracted to construct the failure probability function. The method is computationally efficient, is flexible to implement, and is well suited for geotechnical problems that may involve sophisticated models. A design example of two-dimensional deep excavation against basal heave is discussed for Singapore marine clay where the density and normalized undrained shear strength of soil mass are modeled as random fields. Results demonstrate that the proposed method works well in practice and is advantageous over the coupled or locally decoupled reliability-based geotechnical design methods.