It consists of a parallelepiped body (1) comprising a lower zone (2) provided with supports or legs (3) located in the corners, on which an upper parallelepiped zone (4) is connected, said upper zone having a trapezoidal section and with a lower central rectangular projection (6) and an upper rectangular recess (5). Both zones (2, 4) have the same length, but are offset linearly in order to define complementary tongue-and-groove coupling means for in-line assembly. The rectangular recess (5) define the bed for laying the submarine outfall or pipeline, the bed being covered with slabs (9) which are fixed to the upper zone (4) with rods. The elements or bodies (1) are also fixed to one another with vertical rods (15).