Environmental Engineering Reference
In-Depth Information
size smaller than 1 mm (the limit of penetration of cement particles), but without a signifi-
cant clay portion. Although substantially more costly than cement grouts, additives allow
very short set times, of the order of minutes, if necessary. Since silica gels have a viscosity
approaching that of water and contain no solid particles, penetration is usually excellent.
Epoxy resins
are relatively new, and are finding many applications such as to seal piping
channels or small flow channels in soils and rocks, as well as basement walls, etc. They are
relatively expensive but offer a number of advantages. They react normally under adverse
conditions, whether the medium injected is corrosive or not, in acid or alkaline environ-
ments, organic soils, etc. Viscosity can be controlled to permit adaptation to any soil or
rock type that will pass water, and the hardening time can be varied from slow to quick
by the use of additives. Injected with simple equipment, epoxy resins can be dissolved in
inexpensive solvents, such as alcohol. The finished product is of high quality, resistant to
physical changes such as compression and failure by rupture or bending, and has almost
no appreciable shrinkage. Since it is strong, but not completely rigid (as are cement
grouts), it permits deformation without fracturing when set in a soil or rock medium,
which is especially important along contact zones of differing materials.
Installation
A grout curtain injected in a single line of holes installed in a soil or rock formation will
often suffice to control seepage. The curtain is thickened by adding rows of grout holes if
necessary. During installation checking grout-curtain effectiveness is necessary and is
accomplished in rock masses with water-pressure or Lugeon tests (Art. 3.3.4). The limits of
water losses given in
Table 8.8
may be used as a standard for grout curtain effectiveness
(Fecker, 1980). Since the Lugeon criteria of 2 liter/min/m at 20 kg/cm
2
pressure for dams
is a criterion seldom achieved, the criteria of Terzaghi and the Water Reservoir Commission
represent an upper limit. Lugeon tests are performed and records kept and plotted, includ-
ing the number of bags of grout used for each grout hole. Grout holes are added until the
desired Lugeon value is obtained.
Occasionally, grouting will achieve a complete cutoff, but it is generally difficult to
obtain 100% penetration, especially in rock fractures or where conditions of high ground-
water flows persist. Cedergren (1967) states that to achieve a 90% reduction in permeabil-
ity in the grouted zone, 99% of the cracks must be grouted; therefore, grouting results in
only a partial control of seepage.
TABLE 8.8
Recommended Satisfactory Water Loss in Water-Pressure Testing for Grout Curtain Effectiveness
Reference
Satisfactory Water Loss(L/min/m at 10 kg/cm
2
Pressure)
Lugeon (1933)
H
30 m
1
a
H
30 m
3
Heitfeld (1964)
H
100 m
3
H
50 m
4
H
20 m
4, 8
Terzaghi (1929)
5
b
Water res. comm. std.
7
b
Int. Teton Dam Rev. Group (1977)
18
Source:
After Fecker, E.,
Bull. Int. Assoc. Eng. Geol.,
21, 232-238, 1980.
a
Criteria seldom achieved.
b
Suggested upper limit of loss.
