Porosity and pore pressure sign convention

[jmeier]

Dear Moose community,

I'd like to double-check two things with you:

First, sign convention in SoildMechanics and PorousFlow:

In #20999, some info on the sign convention in SoildMechanics (formerly TensorMechanics) is given:

It is the same convention as TensorMechanics, which is:

• a positive strain is extensional, which (usually) results from a positive (tensile) stress;
• a negative strain is compressional, which (usually) results from a negative (compressive) stress

Just to be sure, I'd like to spell it out for the pore-pressures:

• Compressive pore-pressures (e.g. below a free water table) have a positive sign?
• Suction is represented by pore-pressures having a negative sign?

Is this correct?

Second, the physical unit of the permeability

PorousFlowPermeabilityConst allowes to input a "permeability"-tensor (internally stored in PorousFlowPermeabilityBase._permeability_qp). It is correct, that the physical unit of the items of this permeability-tensor is "length to the power of two" (e.g. squaremeters, m²)?

Thanks for you help in advance.

[GiudGiud]

@cpgr

[GiudGiud]

or @1runer ?

[cpgr]

Yes and yes (mostly). The units will be m^2 if everything else uses 'typical' units like Pa, kg/m^3 etc