A generic approach to soil–structure interaction considering the effects of soil heterogeneity

The longitudinal variation of soil properties has a major influence for many types of structure, including pavements, buried pipes, raft foundations and railways, as it induces stresses and/or displacements that cannot be predicted when assuming soil homogeneity. A set of simple numerical models has been developed to describe how soil–structure interaction can be influenced by soil variability. These models include: (a) a description of the soil spatial variability, within the frame of geostatistics, where the correlation length of soil properties is the main parameter; and (b) a mechanical description of the soil–structure interaction, which depends on the structure resting on the ground. There are some differences between a (more or less) rigid raft on piles, a set of buried pipes with (more or less) flexible connections and a hyperstatic beam, but the basic principles of mechanics are similar in all these cases. Several very general conclusion are drawn. (a) Soil heterogeneity induces effects (differential settlements, bending moments, stresses and possible cracking) that cannot be predicted if homogeneity is assumed. (b) The magnitude of the induced stresses depends on three factors: the magnitude of the soil variability (i.e. its coefficient of variation); a soil–structure stiffness ratio (in some cases, where the mechanics are more complex, one can consider two stiffness ratios, as in buried pipes for example, when one has to account for the flexibility both of the pipes and of the connections); a soil–structure length ratio, which combines the soil fluctuation scale and a structural characteristic length (distance between supports, buried pipe length, etc). In all cases, a worst value, corresponding to the value leading (from a statistical point of view) to the (statistically) largest effects in the structure, can be found. The principal benefit of such an approach is to provide some new approaches for better considering phenomena such as the geometrical irregularities in the longitudinal profile of pavements or during the control of soil compaction of sewer trench filling. This kind of approach can also give experts new tools for better calibration of safety in soil–structure interaction problems, when the soil variability is an influential parameter. Some practical conclusions are drawn in this direction.