Environmental Engineering Reference
In-Depth Information
Table 18.4.
Relationships of different mix proportions of cement and water in grouts.
Water : Cement by volume
Water : Cement by weight
Cement : Water by weight
6:1
4:1
1:4
(0.25)
4:1
2.67:1
1:2.67
(0.37)
3:1
2:1
1:2
(0.5)
2:1
1.33:1
1:1.33
(0.75)
1.5:1
1:1
1:1
(1.00)
1:1
0.67:1
1:0.67
(1.50)
because it depends on bulking of the cement. Table 18.4 gives approximate relationships
given by Deere (1982).
Deere (1982) advocates the use of unit weight of the cement grout slurry measured by
a “mud balance” and a marsh funnel to measure viscosity as part of the control of grout
quality in the field. There is some merit in this suggestion as grout penetrability is depend-
ent on viscosity. However, a marsh funnel measures apparent viscosity and, as discussed
in Fell et al. (1992), yield point stress may be more important when considering grout
penetration near refusal.
The selection of water-cement ratio is to an extent related to the “stability” of the grout
mix. As outlined by Deere (1982) stability is measured by a sedimentation test in which a
litre of grout is placed in a standard 1000 ml graduated cylinder. At the end of 2 hours the
volume of clean liquid that has formed at the top of the cylinder due to sedimentation is
noted. This volume, expressed as a percentage of the total volume, gives the percentage
“bleeding” or sedimentation. Grout with a high WC ratio is “less stable” and bleeding or
sedimentation is large.
Addition of small percentages of properly hydrated bentonite improves the stability. Deere
(1982) indicates that in European practice a stable mix is one which has less than 5% sedi-
mentation. Addition of 2% bentonite results in a small increase in viscosity of the grout but
improves stability markedly.
WC ratios which should be used for grouting are discussed in some detail by Houlsby
(1977, 1978 and in WRC, 1981), Deere (1982), Deere and Lombardi (1985), Bruce
(1982) and Bozovic (1985). The authors favour the approach of Houlsby (1977, 1978,
1985) who recommends use of WC ratio (by volume) of not more than 3:1 and indicates
doubts on long term durability if grout with WC ratios greater than 5:1 are used. He rec-
ommends use of the thickest possible mix at all times and suggests the following:
Starting Mix:
2:1
most sites
3:1
for rock
5 Lugeons
1:1
30 Lugeons
0.8:1 for very high losses
4:1 for heavily fractured, dry rock
5:1 rock above water table where excess water is absorbed by the dry rock.
Thicken the mix:
for rock
- to deal with severe leaks;
- after 1
1
⁄
2
hours on the one mix with continued take (except for 1:1 and thicker
mixes);
- if hole is taking grout fast, e.g.
500 litres in 15 minutes.
He indicates further that thickening should be in small increments, e.g. 3:1 to 2:1 and
suggests reapplication of grout to the hole if take has exceeded 0.25 litres/cm of hole for WC
