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The next problem is how to trace and locate leaks when the drop in water level exceeds that allowed in the specification. This should present no difficulty with elevated structures, but for those on or in the ground where the underside of the floor can't be inspected, and sometimes the lower part of the walls as well, considerable difficulty can arise.
The author has recommended in his book Swimming Pools, that it's worthwhile to spend a little more money than is usual on the under- drainage of the floor. This will enable the underfloor system of drains to be laid in such a way that the floor area is divided into a number of separate units as shown in Fig. 9.1. If the external walls are embanked, it's usual practice for a perimeter drain to be laid just below kicker level to drain the embankments. If this perimeter drain is kept separate from the underfloor drainage it will enable leakage through the wall to be seen separately to any flow arising from leakage through the floor. By dividing the underfloor drainage into units, each controlled by a man hole, flow in the system can be monitored, and the search narrowed to a group of about six floor bays.
FIG. 9.1. Suggested layout of underdrainage of reservoir floor to assist in location of leakage.
As previously stated, the most likely places for leakage in a floor are through the joints and these should be carefully examined. Unfortunately, the author’s experience is that there can be considerable seepage through joints without any visible sign of defects on the surface.
All this sounds very depressing, and , to remedy leaks in floors can be very time consuming and consequently expensive. The Hydrology and Coastal Sedimentation Group of the Atomic Energy Research Station at Harwell, developed techniques in the 1960s for tracing leaks by means of short-lived radioactive tracers. The Group carries out the work itself and is responsible for the selection of the tracers used in each case. The technique is expensive, but the standard routine of trial and error may cost even more if accurate costing procedures are adopted. The tracer technique is particularly useful where there is no underdrainage, or the drainage system has no access points.Where underdrainage, as suggested above and shown in Fig. 9.1, has been provided, dyes, concentrated salt solution, etc., can be used to supplement visual inspections at manholes. However, it must be remembered that dyes will stain the surface of the concrete as well as most other materials. This is important when the structure has already been given a decorative finish, for example a swimming pool.
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