A Reminder: Hydraulic Conductivity of Jointed Rocks for Water and Grout
Mahdi Zoorabadi
Technical Principal - Geotechnics & Tunnels at SMEC (BSc,MSc,PhD)FIEAust, CPEng(Geotech & Civil) NER; Adjunct Assoc. Prof, UNSW
This topic is a bit old fashion, but I found it very important when we discuss about groutability of the jointed rocks. Hydraulic conductivity (K) is parameter which presents how easily a fluid with the known viscosity and density flows through the rock mass.
k is permeability, which is independent from the fluid characteristics, g is gravitational acceleration, is density and is the fluid viscosity (it is equal with 0.8891 mPa.S for water at 25 oC). Certainly, when we conduct the packer test/slug test or pumping, the results represent the hydraulic conductivity of jointed rocks (m/s) for water. Based on this equation, the hydraulic conductivity decreases with increasing of viscosity.
The viscosity of grout changes with water/cement ratio from above 100 mPa.S for W/C=0.4 to 10 for W/C>0.7 (Raffle & Greenwood, 1961). Then for example, if we are injecting a cement grout into the rock mass where the measured hydraulic conductivity is 1e-6 m/s, the hydraulic conductivity for this grout would be approximately 1.7e-8 m/s and 1.4e-7 m/s for the W/C=0.5 and W/C=1 respectively.
ADB Consultant, Professional Engineer, University Professor, 15 years Experience in large infrastructure (Dam,Tunnel and Road)
3 年SAEED AHMAD
Technical Director, Tunnelling
3 年Thanks Mahdi but I am struggling to understand your "punch line" here. Firstly, a rock mass with 1e-6m/s is equivalent to something close to 10 lugeons so obviously groutable if your grout holes intersect the right features. Secondly, we cannot forget the role of pressures when grouting. Just compare the default pressure in a packer testing with those used in high pressure grouting. Thirdly, who starts a grouting campaign with w/c<1? Grout is generally thickened as part of the grouting process. We could also add to the discussion the type of cement: OPC versus microfine versus UFC. So with all of that, what was the objective of the post?