Closure to “Rock Fracture Spacings, Openings, and Porosities”

The Comments of Houlsby, Scott and Wittke Concerning Fractures and Grouting Are Discussed. As Noted, Grout Takes Usually Correlates Poorly With Permeability. The Paper Suggests That Grout Take Be Correlated With Porosity, Permeability Has Commonly Been Correlated on the Premise That Grout Moves With the Same Ease During the Entire Period of Injection, So That Rate Times Time Varies With Permeability. Permeability Is an Inadequate Correlation When Viscosities of the Fluids Differs. Resistance Increases Continuously as the Medium Is Invaded to Greater and Greater Distances. A Volume of Porous Medium Is Therefore Delimited, Within Which There Is Partial Saturation by Grout. The Degree of Saturation Depends on the Fracture Pattern and Aperture Distribution. Scott's Discussion Is a Welcome Independent Confirmation of the Fracture Openings to Be Expected at Depth in Fractured Foundations. Discussion Is Made of Wittke's Feelings That Joints Are Non-Random in Rock Bodies, Thus Invalidating the Assumption That Equal Lengths of Drill Hole, Disposed and Oriented at Random, Cut Numbers of Fractures Distributed as a Poisson. The Poisson Estimate Seems Acceptable in View of the Magnitude of Errors of Derived Properties. A General Expression Is Presented for the Hydraulic Conductivity of Planar Conduits. The Expression Is Presented for the Reynolds Number for Radial Flow Between Parallel Plates. Little Error in Derived Porosities or Openings Could Have Been Introduced by Neglect of Turbulence References: Rock Fracture Spacings, Openings, and Porosities, David T Snow, Asce Proc. Paper 5736, January 1968.