Theory and Method
Water crosses a geosynthetic barrier two ways, and the GHPT C series separates them. An intact membrane passes water only through permeation, where molecules dissolve into the polymer on the pressurized face, diffuse across the thickness, and leave on the far side. Flaws work differently. Pinholes, thin spots, fiber channels in composite products, and gaps in a laminate bond all offer open paths, and water pushes through them in bulk once applied pressure overcomes the surface tension holding it back.
Hydrostatic resistance testing hunts for that second mechanism. The pump raises pressure in defined steps and holds each step for a set interval while the operator watches the downstream face. Nothing shows as long as the applied head stays below what the largest flaw can resist. Water breaks through once pressure crosses that point, and the step at which it happens becomes the reported hydrostatic resistance. The result answers a pass/fail question: does this material hold the head the project demands?
Permeability testing runs below the breakthrough point and measures flow rather than failure. Darcy's law relates steady flow to the coefficient through k = QT / (AtΔH), where Q is the permeated volume, T the specimen thickness, A the exposed area, t the elapsed time, and ΔH the head difference. Two conditions have to hold. Pressure stays constant across the interval, and flow reaches steady state before the reading counts, since early volume includes water still saturating the material. Perforations of ø3 mm drain that flow toward the collector while supporting the specimen against 2.5 MPa, so the membrane deforms into small openings instead of tearing across an unsupported span.
