Environmental Engineering Reference
In-Depth Information
normal to the face slab, and parallel to the joint due to shear movement of the face. The
joint is a common cause of leakage if not well designed, constructed and inspected.
Table 15.8
summarizes maximum perimetric joint movements measured on a number of
CFRDs.
To accommodate these movements, joints with multiple water stops are provided.
Figures 15.15
,
15.17
to
15.20
show some examples.
The design shown in Figure 15.17 for Reece Dam is typical of practice up till around
the mid 1980s. The joint includes two water stops
-
Primary - copper or stainless steel “W” or “F” shaped;
-
Secondary - central “bulb” water stop made of rubber, hypalon or PVC.
Cooke and Sherard (1987) indicate that this arrangement has performed adequately on
dams up to 75 m high, where perimetric joint movements are generally relatively small.
Fitzpatrick et al. (1985) indicate that in two dams, 39 m and 26 m high, only the primary
water stop was used because very small movements were expected.
More recently, particularly for higher dams, a third water stop has been included in the
form of mastic or fly ash filler covered with a PVC or hypalon sheet. These are shown in
Antamina dams. Cooke and Sherard (1987) argue that, because of the difficulty of having
concrete around the central “bulb” water stop, they believe that a joint with the copper
(or stainless steel) water stop underlain by asphalt impregnated sand or concrete mortar
and the mastic type stop, is the preferable detail. For Antamina dam (Amaya and
Marulanda, 2000) the intermediate PVC seal was eliminated and a 1 m thick sand zone
(2A) placed under the perimeter joint. These modifications were incorporated to ease con-
struction and control potential seepage in joints that have performed well in practice.
It will be noted that in the designs shown, a wood plank approximately 12.5 mm to
20 mm thick, or some other compressible filler of similar thickness, is placed between the
face slab and plinth to prevent concentration of stresses in the joint during construction
and before reservoir filling.
15.3.3.2
Water stop details
Primary copper or stainless steel water stop
. These are either “W” or “F” shaped, with a
high central rib to permit shear movement between adjacent slabs. To prevent external
water pressure from squeezing the rib flat, it is filled with a neoprene insert, 12 mm diam-
eter, held in place with a strip of closed cell polythene foam 16
12 mm (Fitzpatrick et al.,
1985). The water stop is supported on a cement mortar or asphalt impregnated sand pad.
Fitzpatrick et al. (1985) indicate that the HEC seated the water stop on a 400 mm wide
strip of tar impregnated felt (“malthoid”).
Whether copper or stainless steel is used depends on the aggressive nature of the reser-
voir water, but also seems to be a matter of individual designer preference, with copper
being more common. Fitzpatrick et al. (1985) indicate that for the Reece Dam the HEC
departed from its earlier practice of using copper water stop (annealed after forming to
give maximum ductility) and used 0.9 mm thick grade 321 stainless steel. This was done
because it was considered that the stainless steel would be “more robust” during con-
struction, and there was not a significant cost differential, and the stainless steel would be
less affected by the acid reservoir water.
ICOLD (1989a) indicate that it is advisable to form the copper or steel water stops in
continuous strips to minimize the need for field splices. They recommend use of an elec-
trode of high fluidity (silver content greater than 50%) for welding copper waterstops to
ensure full penetration into the two copper plates, then checking with a spark tester to
ensure a good joint has been achieved. Fitzpatrick et al. (1985) indicate that for stainless
