this report describes an examination of the defects and other features observed in closed circuit television (cctv) surveys of 6 km of sewers. the defects were classified using a purpose developed coding system, and recorded and analysed using a suite of computer programs. the frequency and distribution of defects, and their relation with environmental and construction factors, were examined. a large number of defects (about one per metre run) were found, but only a small proportion of them are likely to have any serious immediate effect on sewer efficiency or integrity. most of the environmental and construction factors considered are not completely independent of each other, but it was clear that type of road, depth to invert, pipe length and bedding, position of water-table, and age, were important in relation to frequency of defects. implications for structural design, cctv surveys and further work are discussed.(a)

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