Parameters that influence the pressure filtration characteristics of bentonite grouts

The pressure filtration of grout, pressurised against fine sand, has been investigated in a laboratory set-up. The grout mixtures that were tested consisted of water and bentonite, together with cement, fly ash, silica Hour and/or retarder. Samples were subjected to a pressure of 100-400 kPa. The permeability of the grout cake formed during pressure filtration was calculated from the results. It appears that the permeability of the grout can differ by more than three orders of magnitude, depending on the grout sample tested. Adding cement increases the permeability. The grain size of the material in the mixture had minimal influence. Mechanisms are discussed.