Stiffness and strength properties. Numerical codes offer a set of advanced models for the analysis of the mechanical behaviour of soils. Naturally, advanced approaches require in parallel an advanced soil characterization. Laboratory testing has the advantage of directly measuring the mechanical soil parameters, but generally cannot be performed on granular soils unless using sophisticated sampling procedures, because of the difficulty to recover high quality samples. To this end, penetration tests are currently adopted. These have the advantage to investigate the soil response with continuity along one or more verticals. Both standard (SPT) and cone penetration tests (CPT) allow to evaluate the relative density Dr and the friction angle ϕ’ through empirical correlations. This is also the limit of the approach. Similarly, empirical correlations can be found linking the Young modulus E to the cone resistance qc (Xxxxxxxxxxx et al., 1978; et al.). The characterization of fine-grained soils can be obtained by laboratory tests. For most applications on saturated soils, a conventional triaxial apparatus is sufficient. The Young’s modulus, E, and shear modulus, G, which govern the elastic behaviour of soils can be obtained from the initial stage of a drained triaxial compression test by plotting the deviator stress, q, against the axial, εa, or deviator strain, εq. Note that other devices, such as the oedometer apparatus, or field geophysical tests, can be used to infer the elastic properties of soils, but the obtained parameters are not individual properties (E, ν or G, K), but some composite quantity which can provide one of these parameters, if assumptions are made about the others (Wood, 2004). The Xxxx-Coulomb failure criterion is most commonly adopted in elastic-perfectly plastic models. An elastic-perfectly plastic model with a Xxxx-Coulomb failure criterion requires the definition of the elastic properties and of some strength properties: for example, the maximum angle of shearing resistance used to analyze drained problems, or a limiting shear stress used to analyze undrained conditions in cohesive soils, in conjunction with some information about the induced volume change through, for example, an angle of dilation. In this case too, compression triaxial tests can be used. The value of the parameter M, which defines the yield function, can be related to the angle of shearing resistance ϕ of the soil, while the definition of the plastic potential function which describes the plastic defor...
