who is raising pressures rapidly with concurrent thickening of mixes to
reach the maximum pressure as quickly as possible. However, the inspec-
tor who has learned the grouting characteristics of the hole by noting the
change in injection rate for each added increment of pressure and who has
observed and recorded the effects of each new mix on both the injection rate
and the pressure has a good chance to notice out-of-character responses in
the behavior of the hole. If the grouting pressure is close to the estimated
maximum safe pressure and the injection rate quickens with a slight drop in
pressure, lifting should be suspected.
(3) Washing pump system and grout holes. Although care and mainte-
nance of equipment are properly a function of the contractor, maintenance
needed to avoid jeopardizing a grouting operation should be directed by the
inspector and provisions there for made in the specifications. Such mainte-
nance includes keeping the pump system clean and in good operating condi-
tion during the grouting process. The pump system should be flushed with
water at intervals that will vary with temperature, mix, and rate of injection.
During extended periods of continuous grouting with thick mixes, it may be
necessary to wash the system as often as once each hour. C o n s i d e r a t i o n
should be given to injecting several cubic feet of water into the grout hole at
about the same frequency when using thick mixes, if not contrary to the ob-
jectives of the grouting program. (Washing or flushing to rejuvenate a hole
may not be compatible with efforts to construct a narrow grout curtain. )
Water is usually injected into a grout hole when grouting is suspended due to
an emergency, or when it is stopped intentionally to permit grout already
placed to set. This is done to maintain access to a readily groutable zone
or cavity for additional grouting from the same hole. Every effort should be
made to keep mixes thicker than 1:1 constantly moving. A very brief delay
may cause the loss of the hole. Occasionally loss of hole from emergency
delays can be prevented by jetting a pipe to the bottom of the hole and flush-
ing out the stiff grout. This should be quickly followed by pumping a batch of
water into the hole and, if that is successful, using a thin mix to resume
grouting operations.
(4) Sudden refusal. The sudden refusal of a hole to take grout suggests
s e v e r a l possibilities. Extraneous solid matter may have fallen into the grout
and blocked the line, the packer, or the hole; the hole above the zone taking
grout may have collapsed; the mix may be too thick; or the openings in the
rock may be full. The various possibilities should be checked unless sudden
refusal is routine at the site involved. First, if the injection rate is not quite
zero, an attempt should be made to reopen the hole by pumping water into it.
If this does not work, the grout line to and through the packer, if a packer is
used, should be examined to-make certain that grout is reaching the hole. As
a last resort a probe can be dropped in the hole to learn whether it is open.
The addition of an inert filler to the grout sometimes causes sudden stoppage
in a hole. Fillers should be added cautiously if large, cavities are not known
to be present. The filler should be taken out of the mix immediately if it
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