Investigating mechanism of inclined CPT in granular ground using DEM

Abstract

This paper presents an investigation on mechanism of the inclined cone penetration test using the numerical discrete element method (DEM). A series of penetration tests with the penetrometer inclined at different angles (i.e., $$0^{\circ },\,15^{\circ },\,30^{\circ },\,45^{\circ }$$ and $$60^{\circ }$$ ) were numerically performed under $$\mu =0.0$$ and $$\mu =0.5$$ , where $$\mu $$ is the frictional coefficient between the penetrometer and the soil. The deformation patterns, displacements of soil particles adjacent to the cone tip, velocity fields, rotations of the principal stresses and the averaged pure rotation rate were analyzed. Special focus was placed on the effect of friction. The DEM results showed that soils around the cone tip experienced complex displacement paths at different positions as the inclined penetration proceeded, and the friction only had significant effects on the soils adjacent to the penetrometer side and tip. Soils exhibited characteristic velocity fields corresponding to three different failure mechanisms and the right side was easier to be disturbed by friction. Friction started to play its role when the tip approached the observation points, while it had little influence on rotation rate. The normalized tip resistance $$(q_{c}=f/\sigma _{v0})$$ increased with friction as well as inclination angle. The relationship between $$q_{c}$$ and relative depth $$(y/R)$$ can be described as $$q_{c}=a\times (y/R)^{-b}$$ , with parameters $$a$$ and $$b$$ dependent on penetration direction. The normalized resistance perpendicular to the penetrometer axis $$q_{p}$$ increases with the inclination angle, thus the inclination angle should be carefully selected to ensure the penetrometer not to deviate from its original direction or even be broken in real tests.