The procedure consists of installing friction elements in the form of one or more lengthwise flexible cables (6, 7) to counteract buoyancy on the inspection chamber (1). The cables extend for some 5 m on either side of fastening lugs (4). They have a stretch limit of one per cent under the force applied to the chamber, and can be metal cables enclosed in plastic sleeves, or of reinforced polymer. A variant can use galvanized iron or plastic sheets in place of the cables.
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