в следующем контексте:
For installing pipework underground, the excavation area must be carefully prepared to an adequate size with a bed of sand of at least 100 mm before the installation. All the pipework can be freely positioned with the clever avoidance of damage during laying and jointing. It will be manually supported for half of the pipe diameter by compacting by walking along by foot and refilling to the upper line compacted pipe, then compacting with the feet again. One then goes on to pile up a layer of 150 mm and compaction by machine provided that it is not directly over the line of the pipe ( the support and the refilling up to 150 mm above the upper line of the pipe can be made in a single operation when the material used is sand or loose riddled soil); the available material for the remaining re-interring can be used compacted in layers of thickness not greater than 250 mm, provided that it is not compacted directly above the line of the pipe, until reaching 300 mm in height above the upper line of the pipe.

смысл этого предложения в том, что трубы сначала укладываются в ручную и песок утрамбовывают ногами до тех пор, пока плотный слой не дойдет до половины диаметра трубы