Environmental Engineering Reference
In-Depth Information
Figure 18.21.
Typical arrangement of grouting equipment (Houlsby, 1977, 1978, and WRC, 1981).
use of high water/cement ratio grouts which were “unstable” (i.e. settled out) and the
requirement for a bypass valve to control injection pressure.
Details of bleeder valves and bypass, flowmeters, pressure gauges and standpipe fittings
are given in Houlsby (1977, 1978), WRC (1981) and Gourlay and Carson (1982).
Packers for use in grout holes are either mechanically operated from the surface by a
screw device, or inflatable, expanded against the side of the hole by compressed air or
water. The length of “seal” formed by mechanical packers is often only 0.3 m, compared
to 0.5 m to 1.5 m for the inflatable type, so leakage past the packer is more likely with the
former. Mechanical packers would usually only be adopted if rock conditions resulted in
puncturing of inflatable packers.
18.3.5
Water cement ratios
Cement grout mixes are usually designated by water cement (WC) ratios, with mixes
ranging from 6:1 WC (by volume) to 0.6:1. Most grouting uses mixes of 2:1 WC ratio or
less, as it is well documented that higher WC ratios yield unstable mixes (i.e. the particles
settle quickly) and the grout is of poor durability (see Houlsby, 1985; Deere, 1982; Deere
and Lombardi, 1985 and Alemo et al., 1991).
Use of volumetric WC ratios has been traditional in Australian and USA practice
because a bag of cement was taken to be one cubic foot and as such was an easy measure
in the field. The relationship between volumetric and weight based ratio is approximate
