Strength and Stability of Regoliths in Low Confining Stress

One of the most used models in planetary science, geotechnical, and geophysical studies to describe the strength and behaviour of geological materials such as regolith is the Mohr-Coulomb equation. However, the Mohr-Coulomb equation is actually a linear approximation to a non-linear failure envelope and is not appropriate in very low-confining stress conditions. This has been widely documented in the geotechnical literature but, as far as we are aware, the consequences of the non-linearities in very low confining stress are not commonly considered in the context of small bodies. Indeed, on small bodies, where the gravitational acceleration and thus confining stress can be several orders of magnitude less than on Earth or the Moon, the surfaces should operate in a non-linear strength regime.

The primary goal of this work is to bring established models and literature from the geotechnical engineering community about the non-linear failure envelope to the attention of the planetary science and exploration communities. Then, using an established non-linear failure model, we demonstrate the consequences of non-linearity in the limit of extremely low confining pressure for both the surface and sub-surface mechanical properties of small planetary moons, asteroids and comets. We also discuss implications of the non-linearities for surface stability and regolith mobility, small body surface interactions, numerical modelling, laboratory experiments and planetary simulants.

This work is supported by the European Research Council GRAVITE project (grant N°1087060).