Abstract: A flexible mattress-like element usable as ballast or a load for immobilizing and protecting underwater pipelines, includes an outer flexible envelope, preferably made from a non-woven fabric, covering at least one gabion which is made from double-twist, hexagonal-mesh wire netting in the form of a somewhat-flattened parallelepiped and is filled with a mixture of stones or pebbles with a sand-, filler-, and bitumen-based mastic. The composition of the mastic is such that it is fluid at 150.degree. C. to 180.degree. C., semi-fluid at 100.degree. to 140.degree. C., plastic at 10.degree. to 50.degree. C., semi-plastic at temperatures of from 0.degree. C. to -10.degree. C., and tends to become rigid at temperatures below -10.degree. C. Each gabion is made from panels of netting in which the portions of wires which are twisted together are preferably arranged transverse the length of the gabion, that is, parallel to the axis of the pipeline to be immobilized and protected.

Abstract: According to the invention, the articulated connection of a "diaphragm" to the "base panel" of a gabion is carried out by bending divergent portions of pairs of wires twisted together along common sides of the diaphragm's hexagonal meshes in the marginal row of these meshes which is to be connected to the base panel so as to dispose each of these portions within the hexagon of which it constitutes a side so as to be substantially parallel to that portion of the same wire which extends from the other end of the common side of two adjacent hexagonal meshes which the two wires are twisted together to form; the double-hooked structure which is thus obtained is then anchored to meshes of that part of the base panel intended to form the bottom of the gabion, these meshes being in the same row extending between two parallel edges of the panel itself.