Hi

Swelling Pressure

Swell pressure is defined here as the pressure required to compress the specimen, that has been soaked and completed the swell under 3.89kPa pressure, back into its original configuration (before swell). 

Compressibility Characteristics

The virgin compressibility is defined as the linear part of the volumetric strain (ev) vs. logpressure (p) curve under virgin loading path.

Please refer this pdf

http://puslit2.petra.ac.id/ejournal/index.php/civ/article/viewFile/15575/15567..

Both Values are more or less same in the aspect of diffused double layer thickness.  

Kabilan Nagappan provided good answer.

Dear Ali

you can read these files