Similitude requirements for modelling NAPL movement with a geotechnical centrifuge

The scaled modelling of non-aqueous phase liquid (NAPL) transport in porous media is examined with particular reference to the use of a geotechnical centrifuge as a tool for modelling this phenomenon. Scaling relationships for NAPL mobility are derived. These relationships suggest that when the controlling length for a problem is macroscopic, similitude between a centrifuge model and the prototype can be achieved; otherwise, direct scaling of data from a centrifuge model to the prototype is not possible. Three examples of centrifuge studies that investigated different categories of subsurface NAPL movement are presented. By analyzing these studies, it is shown that bulk NAPL migration and gravity-driven wetting front instability can be correctly scaled using a geotechnical centrifuge; however, NAPL entrapment by capillary forces can not be thus scaled.