Environmental Engineering Reference
In-Depth Information
10.4.4
Grout diaphragm wall
Grout diaphragm walls are excavated continuously in panels as shown in Figure 10.18,
with the trench supported by a cement/bentonite slurry. This slurry is left in the trench and
cures to give a low strength, low permeability compressible wall. The panels are excavated
in the sequence shown in
Figure 10.17
,
with the secondary panels being excavated before
the slurry has hardened excessively in the primary panels but has hardened sufficiently to
be self supporting. This obviates the need for end support for the panels as is used for cast
in place diaphragm walls (see
Section 10.4.5
).
The trench may be between 0.5 m and 1.5 m wide (ICOLD, 1985) but will often be
nearer the narrow limit for economy.
Excavation is carried out by grab buckets or clamshells. While ICOLD (1985) make no
definitive statement on maximum practical depth, it can be inferred that grout diaphragm
walls may be used to at least 50 m depth.
(ICOLD, 1985) indicate that the cement/bentonite grout will usually have the follow-
ing composition per cubic metre of grout:
- 80-350 kg cement;
- 30-50 kg bentonite.
Xanthakos (1979) indicates that typical mixes will be:
- 15-20% cement;
- 2-4% bentonite;
- 5-10% sand and gravel.
The water cement ratio (by weight) will be between:
- 4:1 and 10:1 for ground granulated blast furnace cement (BLF);
- 3.3:1 and 5:1 for Portland cement (P).
Figure 10.18.
Grout diaphragm wall, (1) Order of construction of panels A,B,C,D,E,F,G; (2) ABDF pri-
mary panels, CEG secondary panels (ICOLD, 1985).
