  We numerically study a three dimensional system of athermal, overdamped,
frictionless spheres, using a simplified model for a non-Brownian suspension.
We compute the bulk viscosity under both uniaxial and isotropic compression as
a means to address the question of whether stress-anisotropic and
stress-isotropic jamming are in the same critical universality class. Carrying
out a critical scaling analysis of the system pressure $p$, shear stress
$\sigma$, and macroscopic friction $\mu=\sigma/p$, as functions of particle
packing fraction $\phi$ and compression rate $\dot\epsilon$, we find good
agreement for all critical parameters comparing the isotropic and anisotropic
cases. In particular, we determine that the bulk viscosity diverges as
$p/\dot\epsilon\sim (\phi_J-\phi)^{-\beta}$, with $\beta=3.36\pm 0.09$, as
jamming is approached from below. We further demonstrate that the average
contact number per particle $Z$ can also be written in a scaling form as a
function of $\phi$ and $\dot\epsilon$. Once again, we find good agreement
between the uniaxial and isotropic cases. We compare our results to prior
simulations and theoretical predictions.
