The two papers on exact results for effective constants
in poroelasticity eventually lead to the following paper on
general results for ``effective stress laws.''
Actually, there are many effective stress laws, but the situation
is often oversimplified by stating that there is only one
effective stress = the differential stress, taking the difference
between the confining pressure and the pore pressure.
In fact, there almost as many effective stress rules as there are
physical variables!
