Chrono SCM Implementation - Why No Coulomb Friction?

[Joshua Philip Martin]

I've been reading up on the background for SCM implementations and through the source code for Chrono's own implementation.

I am curious why Chrono's current implementation has elected not to include Coulumb friction in the calculations. For calculating shear stress (and thus, shear forces) at each node, Chrono's SCM uses only the Janosi-Hanamoto model for these calculations. The limitation of the J-H model is that

Meanwhile, this often-cited SCM implementation by Krenn and Herizinger uses a different approach, with Coulumb friction being explicitly included at each node in combination with the max possible Mohr-Coulomb shear stress. This doesn't necessary capture all of the dynamics that J-H does, but it does always return a shear stress when a normal stress is applied (even when shear stress is negligible).

I'm curious as to why Janosi-Hanamoto is used here and what the limits to J-H are in Chrono's context? I can see it being more accurate for moving through very soft soils, but yielding ver little (or zero) shear stress on more rigid soils SCM terrains or when the slip is negligible (say, when a wheel has stopped moving) seems like a limitation. Does the current Chrono limitation account for the fact that J-H returns zero shear stress while a wheel is static?