Values of a and b in skemptons pore water pressure parameter?

Skempton's pore pressure parameters A and B are used to check the saturation of the sample. As when the sample is fully saturated if we increase the cell pressure there will be same amount of increment in the pore pressure too. The reason behind this is that the system acts more like a confined bulb . Similarly the parameter A gives the change in the pore pressure as we increase the deviatoric stress

Δu3=BΔσ3

Δud=AΔσd