Chapter 7
Testing and rectification
7.1 Testing for watertightness The design and construction of liquid-retaining structures require close attention to detail by both the designer and contractor, and in spite of the best intentions of both parties, errors and omissions can occur. Equally, random occurrences, unfavourable statistical conjunctions and insufficient design guidance can result in a structure that is less than completely liquid-tight. It is therefore necessary to test the structure after completion to ensure that it is satisfactory and that it complies with the specification. The method of test depends on the visibility and position of the elements of the structure. The walls of overground structures can be inspected for leaks on the outer face and, if the walls are finally to be backfilled with soil, the inspection can be made before the fill is placed. The walls of underground structures can be inspected if there is sufficient working space available (compliance with the HSE Confined Spaces Regulations 1997 (2009) must be achieved). The floor slabs of all structures built on soil cannot be inspected for leaks, and other methods of test have to be used (CESWI 7th Ed., 2011). The floor of an elevated reservoir (or water tower) can be inspected in the same way as walls, as can the underside of a flat reservoir roof. If the structure is designed to exclude rather than retain water, it is possible to inspect the inside faces of the walls and floors but rarely possible to ensure that liquid is available to make a test, and hardly ever possible to take remedial measures from the outside. An example of this situation is that of a basement of a building that is designed to exclude groundwater. Detailed methods of testing are described in the following sections.
7.2 Definition of watertightness The term ‛watertightness’ although descriptive is not sufficiently precise for the purposes of a contract specification. Essentially, a watertight structure is built to contain (or exclude) a liquid, but some loss of liquid is inevitable due to evaporation or slow diffusion through the concrete. Also, actual leaks may occur through fine cracks in the concrete. As mentioned previously in Chapter 3 these may heal autogenously (i.e. without any treatment); part of this mechanism involves water percolating through the crack and dissolving calcium salts from the cement. As the process continues, the crack is slowly filled and eventually the water penetration ceases. The process may take up to about one week with cracks of 0.1 mm width, but up to 3 weeks for cracks of up to 0.2 mm width. Cracks over 0.2 mm thick may not self-seal at all. (BS EN 1992-3 Clause (113) states that ‘in the absence of more reliable information, healing may be assumed where the expected range of strain at a section 155
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