b. Series Grouting. Series grouting is similar to stage grouting except
that each successively d eeper zone is grouted by means of a newly drilled
hole to eliminate the need for washing grout out-of the hole before drilling
d e e p e r . Holes at regular intervals are drilled to the depth of the first zone
and individually grouted from the top of rock at low pressure. T h e split-
spacing method of reducing the grout-hole interval is followed until the
uppermost zone refuses grout at the permissible pressure. After the first
zone has been completed, another series of holes is drilled into the second
zone and grouted from the top of rock at higher pressures, following the
same procedure as outlined for the first zone. Additional series of holes
may be drilled, depending upon the final depth bf grouting required. The
maximum pressure is applied to the deepest zone. The justification for
using the higher pressures in the deeper zones in this method, and in the
stage-grouting method, is based upon the assumption that a blanket or bar-
rier, as provided by the previously grouted zones, prevents the escape of
grout through, or the development of serious uplift in, the shallower zones.
c. Stop Grouting. In the stop-grouting method of grouting, the hole is
drilled to full depth and a packer used to separate the hole into segments or
zones for grouting purposes. Grouting is started in the lowest zone. After
completion of each zone, the packer is raised to the top of the next higher
zone; and grouting is resumed under a maximum pressure commensurate
with the reduction of overlying load. The packer must be left in place after
each grouting until the pressure on the newly placed grout has dropped to or
below the maximum pressure contemplated for the next higher zone. The
last stop, or packer setting, is at the top of rock. Usually, the packer is not
removed from the hole until the grouting of all stops in the hole has been
completed.
d. Circuit Grouting. Circuit grouting requires the use of a double-line
grouting system (para 17a). The pump line is attached to a pipe that extends
through an expansion plug or packer to within 5 ft of the bottom of the hole.
When grout venting from this pipe fills the hole, if flows through a second
opening in the expansion plug into the attached return line and back to the
grout sump for recirculation. Thus, as soon as the pumping rate exceeds the
rate at which grout is injected into the rock, the grout hole becomes part of
the grout-circulation system. Circuit grouting may be used "to grout a hole
drilled to full depth as a one-time operation, r it may be used as a modifi-
o
cation of any of the other grouting methods described.
e. Soil Grouting. The methods described in the preceding paragraphs
were developed primarily for grouting rock and may or may not be applica-
ble for grouting soil. Because of the lack of stability of borehole walls that
may be encountered in soil, it may be necessary to provide support while
grouting is in progress.
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