grout leaks can be avoided by treating leaks discovered during pressure
testing or pressure washing. At this stage open cracks and fissures may be
filled with a quick-set grout mix. The contractor's responsibility relative to
talking and other treatment of leaks should be described in the specifications.
(7) Completion of grouting.
(a) Grouting may be continued to absolute refusal at the maximum
grouting pressure, although this is not usually done. There are two methods
that are most frequently used to determine when grouting is complete. One
specifies that grouting shall continue until the hole takes no grout at three-
fourths of the maximum grouting pressure. The other requires that grouting
continue until the hole takes grout at the rate of 1 cu ft or less in 10 min
measured over at least a 5-min period. This is often modified according to
the mix and/or pressure used. The second specification is more readily
correlated with pressure-test results than the first.
(b) If there is doubt about the completeness of treatment in any zone or
area, a check hole or holes should be drilled. Such holes can be drilled to
recover core for examination, or they may be drilled for study by the bore-
hole camera or television camera. However, a quicker and less expensive
check can be made by drilling and pressure testing another grout hole. If
tight when pressure- tested with water, the rock is satisfactorily grouted; if
the hole takes water, additional grouting is indicated.
a. Stage Grouting. In this method of grouting, progressively deeper
z o n e s - a r e drilled and grouted in stages from the top of rock. A stage of
drilling is complete when a predetermined depth of zone is reached or when
a specified condition is encountered. A single zone may include more than
one stage. Holes in a given area are drilled to their first stage of depth,
grouting is done at low pressure, and the grout within the hole itself is sub-
sequently removed by jetting or other methods before it has set sufficiently
to require redrilling. (In the event that the contractor is ordered to leave
the grout in the hole for any stage except the last one, payment for drilling
grout is usually made at the rate of 50 percent of' the cost of drilling rock. )
Similar stages or cycles of drilling and grouting are repeated as necessary
to reach the bottom of the first zone. After all first-zone grouting of pri-
mary holes in the area has been completed and a minimum period of 24 hr
has elapsed since completion of grouting operations in any given hole, inter-
mediate holes, located by the split-spacing method, are drilled
Upon completion of all
and grouted to the bottom of the first zone.
h o l e s . the primary holes are drilled to their second zone
odepth and grouted at higher pressures. The process of drilling,
washing, pressure testing, pressure washing, and grouting at progressively
h i g h e r pressures is continued until the ground is satisfactorily tight to the
required depth. If any stage of a hole is found to be adequately tight as de-
termined by pressure testing, grouting of that stage is omitted and the hole
left open for drilling in the next lower stage.