Threshold Gradient for Water Flow in Clay Systems

In this work the presence of a threshold gradient for water flow in clays was established. The threshold gradient is the hydraulic gradient below which no flow occurs. The threshold gradient decreased with decreasing clay concentration and increasing temperature. At gradients above the threshold gradient, the flow rate‐gradient relationship was essentially linear, except at low gradients, for the concentrated clay systems but curvilinear for the less‐concentrated clay systems. These results were explained on the basis of a quasi‐crystalline water structure which developed in the clay‐water systems as a result of water‐surface interaction.