Spatial variations in soil properties and their influence on structural reliability

Abstract

The longitudinal variation of soil properties induces stresses and/or displacements that cannot be predicted when assuming soil homogeneity. The reliability analysis may require a comprehensive modelling on soil–structure interaction, accounting for the spatial distribution of soil properties.

Modelling must account for: (a) the soil spatial variability; and (b) the soil–structure interaction, which is case specific. It is shown that the magnitude of induced effects depends on three factors: (a) magnitude of soil variability; (b) a soil–structure stiffness ratio; and (c) a soil–structure length ratio, which combines the soil fluctuation scale and a structural characteristic length.

A reliability analysis is performed in two cases: a buried set of pipes, and a piled raft. Since a ‘worst value’ of the soil–structure length ratio can be identified, some very practical engineering rules can be derived regarding the definition of characteristic values of the soil properties, which can directly be used in simple models, avoiding both the identification of the stochastic field parameters and the development of sophisticated models.

Keywords:

• Correlation length
• Limit states
• Soil heterogeneity
• Soil–structure interaction
• Spatial variability