Gravitational Drainage from a Granular Bed

The process of one-dimensional drainage of initially saturated granular bed was studied experimentally and theoretically. The permeability-capillary pressure and water content-capillary pressure relationships were determined from the measurements. The suction pressure distribution during drainage was also measured, and the initial condition for Richards' differential equation of flow through the granular bed was experimentally confirmed. Richards' equation was solved numerically by the finite difference method with experimentally determined permeability and capillary pressure-water content relationships. Total discharge and capilary suction pressure distribution data during drainage compare very favourably with numerical results, revealing that the present theoretical treatment and the initial condition for Richards' equation are satisfactory.