The study of soil's small strain dynamic behaviour was the main goal of this dissertation, for the case of a residual soil from Porto granite, a geotechnical material that possess a complex mechanic behaviour. To that end, a detailed experimental research was developed, in true triaxial conditions, considering the measurement of seismic wave velocities through bender elements.
A three-dimensional numerical model was produced that characterized the behaviour of this particular residual soil using a finite difference program, FLAC3D. Its main advantages reside in its simplicity, versatility and the possibility of directly measuring seismic wave velocities, not only in the three principal directions, but also in inclined directions.
This study requires the implementation of bender elements in the platens of the true triaxial apparatus, in order to assess the influence of its cubical geometry and boundary conditions (rigid or flexible platens, or even reflective and absorbent), as well as the validation of stiffness parameters attained from the measurement of seismic waves.
For this purpose, a series of parametric and sensitivity studies were developed, considering the linear elastic constitutive model, with isotropic loading, in the previously mentioned software, to particularly evaluate the influence of each parameter in the numerical modelling of the true triaxial apparatus, and which values are better suited for its correct representation. These parameters are: time step, amplitude, frequency, damping, Poisson’s ratio and finally, boundary conditions and a cross-anisotropic constitutive model. With these studies completed, a comparison and validation between the numerical results attained and the laboratory results previously done by Ferreira (2009), regarding residual soil specimens from Porto granite was in order. Due to time limitations, only the dry specimens (w ≈ 0%), namely, R8D-TT and R4D-K0TT were used in this comparative study.