Environmental Engineering Reference
In-Depth Information
Most foundation grouting uses cement grout: Portland cement mixed with water in a high
speed mixer to a water-cement ratio (mass water/mass cement) of between 0.5 and 5
to form a slurry, readily pumpable and able to penetrate defects in the rock in the dam
foundation.
If the dam is on a soil foundation (e.g. sand) or if the fractures in the rock are very nar-
row, chemicals can be used instead of cement. Chemicals tend to be more expensive so are
only used where cement grout would not be successful. Most soil foundations are not
grouted, with control of seepage being achieved as detailed in Chapter 10.
Foundation grouting takes two forms:
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Curtain grouting;
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Consolidation grouting.
Curtain grouting is designed to create a narrow barrier (or curtain) through an area of high
permeability. It usually consists of a single row of grout holes which are drilled and grouted
to the base of the permeable rock, or to such depths that acceptable hydraulic gradients are
achieved. For large dams on rock foundations, dams on very permeable rock or where grout-
ing is carried out in soil foundations, 3, 5 or even more lines of grout holes may be adopted.
Multiple row curtains are also adopted if, as at Thomson dam, it was impracticable to exca-
vate the foundation to below the limit of the infilled joints.
The holes are drilled and grouted in sequence to allow testing of the permeability of the
foundation (by packer testing) before grouting and to allow a later check on the effective-
ness of grouting from the amount of grout accepted by the foundation (“grout take”).
drain holes
gallery
consolidation grout holes
curtain grout holes
drain holes
Figure 18.2.
Curtain and consolidation grouting for concrete gravity dams.
