appears that it may cause premature stoppage.
( 5 ) Delays. Delays lasting from a few minutes to several hours may be
interposed in the grouting operations to prevent the grout from spreading
beyond a reasonable distance, if in keeping with the grouting objectives. Ac-
celerators may be used in connection with the delays. A succession of de-
lays is sometimes used before a hole is completed. The amount of grout
injected between delays or before the first delay will be a matter of policy
and judgment, which should be based on knowledge of subsurface conditions.
As long as the grout is considered to be fulfilling its intended purpose,
grouting should not be interrupted. There is also the possibility that a c c e s s
from the hole to the void taking the grout will not remain open during the
period of delay, even though water is injected to keep it open. The risk of
losing the hole for further grouting and the cost of a new hole should be
weighed against the cost of the grout saved by the delay before ordering the
delay. If delays of several hours are desired, the contractor's grouting ef-
forts may be directed elsewhere during the period of delay. If the delays are
comparatively short and the contractor is required to stand by with his
grouting equipment, the specifications should state how compensation will be
made for the period of waiting.
(6) Treatment of leaks. Grout sometimes follows interconnected nat-
ural openings in rock to break out many hundreds of feet from the point of
injection.
Frequent and periodic checks of the area in the vicinity of the
grout hole should be made during grouting operations. The inspector should
observe all known wells, springs, or seeps for unusual discoloration or in-
crease in flow. The area patrolled should be enlarged as the grout consump-
tion increases. In the event that a leak occurs, the inspector should estimate
whether it represents essentially all the intake of the grout hole or only a
small part of the total. If all the grout seems to be venting, the pressure
should be reduced, the mix thickened, if not already thick, and a small dike
built to pond thick grout over the leak if possible; then the grouting should be
stopped, The pond of grout will act as a reservoir to keep the vent full until
the grout sets. If only a portion of the injected grout is venting, it may be
worthwhile to expend considerable effort to save the hole. If the leak is in
loose material, the procedure outlined above may be used, except that pump-
ing should not be stopped but slowed to give the thick grout in the pond time
to set. An accelerant may be added to the ponded grout. Sand is a good ma-
terial to create a pond, since excess water in the grout can escape through
it. If the leak is in relatively sound rock, it may be talked with oakum,
wicking, burlap, wood wedges, or lead wool. Burlap is particularly good if
the grout contains much excess water, since it can seep through the burlap
leaving the cement to build up in the fracture. If the grout is not too thick,
brief delays may be tried but without prior injection of water. After the
leaking has stopped, normal operations may be gradually resumed. If the
leaking cannot be completely stopped and represents only a small part of the
grout injected, grouting can be continued at a reduced pressure. Often many
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