Environmental Engineering Reference
In-Depth Information
Figure 10.20.
Typical construction sequence of a diaphragm wall executed in four stages: (a) excava-
tion; (b) insertion of steel tubing; (c) placement of reinforcement cage; (d) concrete place-
ment (Xanthakos, 1979, reproduced with permission of McGraw-Hill).
The steel pipe should have a diameter equal to the trench width, so concrete does not
leak past the tube.
Figure 10.21
shows the effect of overbreak in a gravel layer, allowing
concrete to surround the tube and make it difficult to remove the tube.
Other joint systems may be used to achieve a better contact between adjoining panels and
improve water tightness. Some examples are given in
Figure 10.22
. Millet et al. 1992 give
other examples.
The trench wall thickness is generally 0.6 m for walls up to about 30 m deep, increasing
to 1 m or 1.2 m for deep walls e.g. 50 m. The added width is required to assist in main-
taining overlap between adjacent panels. The usual specified tolerance for verticality is
1/100 or 1/200, with some instances of 1:500 being required (Xanthakos, 1979), Tamaro
and Poletto (1992), Millet et al. (1992).
