A rigid joint assembly for jointing two cables; the assembly includes outer cable entry parts outside a water-tight casing assembly. A first and second cable insulation system deformation preventing devices are provided, each including a rigid pipe, which surrounds a respective first or second cable core end section, and a bedding material layer, which extends at least partially along a length of an inner surface of the respective rigid pipe. The assembly further includes first and second grooved pipes of elastic material having a plurality of grooves on the side facing the cable, each grooved pipe surrounding the respective first or second cable core end section at a respective inner cable entry part inside the water-tight casing assembly 30.