Key in predicting the stability of a rigid body penetrating sand is gaining fundamental understanding of the physics of deformation and failure at high pressures. However, existing mechanical data and constitutive models are based on low pressures and strain rates, therefore they are applicable mainly to civil engineering applications.

The main goal of this dissertation is to extend the knowledge on the mechanical response of sand, to the high pressure (up to 700 MPa) range, which may be encountered in penetration events. To this end, an experimental investigation was conducted on Quikrete^®♯1961 sand and the data used to develop a constitutive model able to describe the observed behavior.

For Quikrete^®♯1961 sand, hydrostatic tests were conducted up to 0.5 GPa allowing for accurate determination of the dependence of the bulk modulus on pressure and the correct estimation of the material's compaction properties when subjected to the high pressures in the range encountered in dynamic events. Triaxial compression tests were conducted at a strain-rate of 10⁻⁵ s⁻¹, and for confining pressures ranging from 0 to 0.3 GPa. During all triaxial compression tests the material exhibited hardening up to failure while both compressibility and dilatancy regimes of the volumetric behavior were observed. Furthermore, the transition from compressibility to dilatancy was found to be highly dependent on the level of confinement.

To investigate the influence of loading rate on the material behavior confined Kolsky bar experiments were conducted at a strain rate of 1000 s ⁻¹. The confined Kolsky bar imposes a constant confining pressure on the specimen through implementation of a high pressure confining cell mounted over the testing section where the specimen is located. Thus, the influence of confining pressure on the dynamic response of the material was investigated for confining pressures ranging from 0 to 0.125 GPa. For all confined Kolsky bar tests no strain rate sensitivities were observed while a clear pressure dependence was observed. Furthermore, in all confined Kolsky bar tests the material exhibited a highly non-linear response with hardening up to the end of loading. For the first time, high quality data that show the influence of confining pressure on the dynamic response were obtained while extending the existing experimental database on sand (the confinements reported in the literature being rather small (less than 6 MPa)).

A new elastic-viscoplastic model that captures the compressibility and dilatancy, as well as strain rate effects has been developed for sand. No a priori assumptions regarding the specific mathematical expressions of the yield function or viscoplastic potential were imposed. It was demonstrated that an associated flow rule doesn't apply. Thus, a new flow rule has been proposed for Quikrete^®♯1961 sand. Comparison between model predictions and data showed the proposed model describes very well the high-pressure behavior of Quikrete^®♯1961 sand.