Abstract1In unsaturated coarse disperse materials such as sand, the water on the surface is continous and ‘deep’ enough to be an adequate medium for the migration of surface active substances (SAS).2The influence of the tangential force on water migration in unsaturated coarse disperse material is studied by compensating the capillary pressure difference caused by the surface tension gradient.3The influence on water migration in unsaturated disperse materials exerted by the additional pressure difference, originating from SAS migration, is comparable to that exerted by capillary pressure differe