be filled in may exhibit so that the nozzles can be arranged on the outside of the edges of the trench 1 for preference a gap is left between the calibrated mouths and the edges of the trench so that the calibrated mouths of the nozzles remain on the outside of the side regions where ground 3 is deposited and so that the jets of water leaving the nozzles can effectively deaggregate and entrain some of the underwater ground into place in the examples illustrated the active parts of the arms 4 and 5 which support the nozzles 6 and 7 are made in the form of two cylindrical tubes of circular cross section the distance between the two tubes increasing from the front backwards the arms 4 and 5 thus delimit a surface of trapezoidal shape in the alternative embodiment illustrated in fig2 the device comprises two sets of balancing nozzles 12 and 13 pointing towards the outside of the device for example lying within a plane perpendicular to the plane of symmetry of the device and preferably exhibiting an upward and outward inclination the sets of balancing nozzles 12 and 13 are mounted respectively on the arms 4 and 5 and supplied with highly pressurized water by the internal conduit of each am in the same way as the sets of main nozzles 6 and 7 mentioned earlier the jets of water emitted by the balancing nozzles make it possible on the one hand to balance out completely or in part the vertical component of the thrust exerted by the main nozzles which tends to lift the device compensating for its apparent weight in water and on the other hand compensate for the outwards sideways thrust exerted by the main nozzles furthermore the balancing nozzles.