Cl
m.
Groutin g
Techniques.
Grouting techniques vary from job to job as
dictated by the subsurface conditions and program objectives, from organi-
zation to organization according to policy, and from inspector to inspector
according to judgment and preference. Some of the procedures and items
subject to modification by policy and field judgment as well as by grouting
objectives are adjustment of mixes, changing grouting pressures, flushing of
grout holes and washing the pump system during grouting, sudden refusal of
a hole to accept grout, use of delays to reduce spread of grout, treatment of
surface leaks, and completion of grouting.
(1)
Mix
adjustment
for
portland-cement
grouts.
(a) The choice of the starting mix may depend on one or more of a vari-
ety of factors: concept of the groutable openings in the rock, time since
drilling, pressure testing or pressure washing, position of water table rela-
tive to the zone to be grouted, and experience with grouting similar rocks. If
the zone is below the water table, if the groutable openings have recently
been wetted, if an appreciable part (but not all) the drill water was lost, or if
the water take in the pressure test was at the rate of about 1 cfm, a starting
mix of 3:1 (3 parts water to 1 part cement, by volume) grout might be the
c h o i c e . If the rock is believed to be dry, or a pressure test result of less
than 0.5 cfm has been obtained, it is likely that a 4:1 or thinner grout would
be selected for starting the hole. If all the drill water was lost and the drill
rods dropped an observable amount, and if the point of the water loss is be-
low the water table or the rock is still wet from pressure testing or pres-
sure washing, the starting mix could be a 2:1 grout. If the hole accepts a few
batches of the starting mix readily without pressure buildup, thicker mixes
should be considered in accordance with the objectives of the grouting pro-
g r a m . In a relatively tight hole with the pressure quickly reaching the max-
imum allowable, the starting mix, if properly selected, should be continued
until grouting is complete.
(b) Mixes are usually thickened by batching the new mix in the mixer
and discharging it into the remaining thinner grout in the sump tank. For
most small grout plants, the grout in the pump system (sump tank, pump,
and both pump and return lines) will have essentially the consistency of the
new grout after the second batch of new mix if the sump is pumped as low as
possible for each batch and the grout lines are, not in excess of 100 ft in total
length. If there is reason for an immediate thickening of the mix, the hole
may be temporarily shut off and enough cement added to the grout in the
sump to obtain the consistency desired in the pump system. Mixing is ac-
complished by agitation in the sump and by circulation through the pump and
l i n e s . Tables or charts showing cement content of various quantities of fre-
quently used mixes are very useful for changing mixes or determining the
amount of cement in a known quantity of grout (figs. 5, 6, and 7). Grout
mixes are thinned by adding water to the sump tank in the amount needed to
obtain the desired water-cement ratio and circulating until all the grout has
the same consistency.
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