(c) A common grouting practice is to thicken the mix until the desired
pressure is reached and continue with this mix until the hole is completed.
Another somewhat more sophisticated practice is to use the mix that will
permit the injection of cement (not total grout mix but cement portion of the
mix) at the maximum rate for a given pressure. Maintenance of the maxi-
mum rate of cement injection will require more frequent mix adjustments
than the first-mentioned practice, but it tends to shorten the grouting period
and reduce the spread of grout. This procedure also serves to guide the in-
spector in the selection of mixes. Groutable openings can be prematurely
blocked and holes lost if the use of too thick grout is attempted. Increasing
the consistency of the grout from 2:1 to 1:1 means that the hole must accept
67 percent more cement for the same rate of grout injection. In many in-
stances it is better to change from 2:1 to 1.5:1 or other mix of intermediate
consistency between 2:1 and 1:1 grout. If one of the objectives of the grout-
ing program is to pump the maximum amount of grout (and cement) into the
rock from each hole regardless of spread, mixes should be kept on the thin
side.
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