Environmental Engineering Reference
In-Depth Information
Figure 18.20.
Principle of grout agitators (Houlsby, 1977, 1978 and WRC 1981).
such high speed mixers “produces a grout which more closely resembles a colloidal solu-
tion rather than a mechanical suspension.” While relatively speaking the grout may settle
more slowly, one should not lose sight of the fact that it still is a suspension of cement par-
ticles which do settle with time.
Having mixed the grout it is usually transferred to an agitator from which it is pumped
to the grout holes. The agitator is relatively slow speed and designed to prevent the
cement particles from settling. Figure 18.20 (from WRC, 1981) shows the principle of the
desired arrangement.
The quantity of grout injected is measured at the agitator.
Grout is pumped from the agitator using grout pumps. Houlsby (1977, 1978) and Deere
(1982) indicate that in Australian and USA practice it is common to use “mono” (or
“moyno”) helical screw pumps because they provide a constant pressure, are rugged and
readily maintained. A grout bypass valve at the hole is required as shown in
Figure 18.21
.
Gourlay and Carson (1982) and Bruce (1982) point out that in British and European
practice there is a preference for ram type pumps, as it is believed the pulsating pressure
assists in preventing clogging of the fracture opening by coarser grout particles. Deere
(1982) also indicates a preference for this type of arrangement, largely because it obviates
the need for a bleeder valve at the hole and/or recirculation line. As pointed out by
Gourlay and Carson, there is a lack of hard evidence to support either preference and one
should be willing to use the equipment readily available. Houlsby (1977, 1978) advocates
the use of a recirculation line of the smallest diameter practicable to keep grout velocities
high and avoid blockage. He suggests the maximum size is 25 mm diameter. Deere (1982)
suggests that the recirculation line is used in US practice because of the then traditional
