Model testing in the NRC wave flume in Ottawa demonstrated the scour-resistance benefit of building submerged sandfill by the Phoenix™ method of pumping water out from the underwater mass during its construction.
The inward flow of water enforced at the water-to-sand interface results in an increase in the normal effective stresses acting on the surficial sand grains. This effect can be visualized either as an increase in particle "weight", or as an "apparent cohesion" affect, on the exposed face.
The above equation which was proposed by Hodge as a full statement of the forces acting on a surficial grain during simultaneous sand jetting and inside drainage was presented at the ASCE Conference linked below.
An improvement in an underwater fill's resistance to erosion is therefore theoretically to be expected during pumping. This proved to be the case.
Other practical implications are that: Pumping water into a longitudinal drain beneath a vulnerable beach during severe storms could limit damage; furthermore, natural beach building could be accelerated by this method.