exist for relatively tight holes or for any hole when the capacity of the open-
ing through the packer is greater than that of the combined groutable open-
ings intersected by the hole.
1. P r o g r a m Objectives. Grouting operations and techniques are not
only influenced by the subsurface conditions encountered, but also by the
purpose and objectives of the grouting program. Is the grouting intended to
be a. permanent treatment, or is it a temporary construction expedient? Is
the tightest cutoff obtainable needed, or is something less than that accept-
able? Should the maximum amount of grout possible be injected into the
rock regardless of spread, or should an effort be made to restrict the spread
to reasonable limits, or should it be restricted to very narrow limits ? The
answers to these questions and the effects of the often overriding factors of
time and cost form the basis for planning drilling and grouting operations.
The treatment of a reservoir to permanently store a liquid pollutant is an
example of one extreme. Sufficient time and money must be allocated and
every effort and decision designed to provide the tightest seal possible,
otherwise the project cannot be successful. At the other extreme, a grouting
program may be conceived to reduce, but not necessarily to stop, seepage
into an excavation during construction as a measure to save on dewatering
c o s t s . Time will be a factor if grouting delays other work. Cost is a factor,
since the saving on dewatering costs must be a ceiling for grouting costs.
Permanence of treatment is not vital in this case, and grouting techniques
are directed toward constructing the most effective cutoff possible for a
specified expenditure of time and money. In the first case, treatment would
probably consist of grouting a curtain of multiple rows of holes to refusal
with the average grout thinner than 1:1. A wetting agent or fluidifier might
be used. Pressures on all intermediate holes would be kept as, high as safety
from lifting permitted. Holes would be grouted each time an appreciable
loss of drill water occurred. Maximum hole spacing after final splitting in
each row would, of course, depend on conditions found, but would likely be
less than 3 ft. In the second case, costs would govern all actions. If holes
were shallow and drilling equipment available, holes would be cheap and
spacings could be split to provide good coverage and keep the curtain nar-
row. If the grouting zone was deep or if drills could not keep ahead of the
grouting, it would be less expensive to spread the grout farther from fewer
h o l e s . Thick mixes and low pressures would be used. Sand or other avail-
able filler would be added to the grout if economical and acceptable for the
openings being grouted. In large openings accelerators would be used to re-
duce the spread of grout. Grouting would be stopped well before refusal to
keep labor and plant costs from being disproportionately high. The objec-
tives of most grouting operations fall between the imaginary example cited
a b o v e . The objectives for all grouting should be clearly defined so that the
designer, the project engineer, and the inspector will understand them and
can then contribute to their realization.
m.
Grouting T e c h n i q u e s .
Grouting techniques vary from job to job as
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