20 / 2025-04-24 11:27:20

FIELD EXPERIENCES ON INNOVATIVE SOLUTIONS AGAINST JET PROPELLER ACTIONS USING ROCK-FILLED MATTRESS FOR SCOUR PREVENTION IN HARBORS

In the last decade port rehabilitation projects are becoming more and more frequent, due to the ever-increasing and powerful propellers of vessels requiring more under-keel clearance when approaching the berth, as well as stronger scour protection systems to prevent instability of the quay walls.
Recent studies have shown that a new innovative form of pre-filled rock mattress, specifically designed and equipped with suited special components to ease underwater launching operations, is becoming a good technically sound and environmentally friendly alternative to conventional loose rock or other conventional protection systems.
This work is going to illustrate two successful project studies where the use of these systems has proven to be a preferable and cost-effective option.
This project study is about an extension of the Lamartine quay in Arles, in France, allowing today 135m long tourist boats to dock and increase river tourism on the Rhône. The protection of the banks against erosion was provided by pre-filled RenoMac Plus.
In order to allow the docking of these larger boats, the Compagnie Nationale du Rhône decided to build a new wharf on the left bank of Arles, upstream from the Pont aux Lions and the Quai Lamartine.
It is planned to install 5 dolphins, install metal walkways with supports based on micropiles and protect the bank with pre-filled rock mattresses.
The objectives of the study was to define a bank protection able to resist the erosion generated by boats during mooring manoeuvres. During these operations, ships use their bow thrusters (propellers located on the side) which generate significant speeds impacting the bottom and the banks of the quays.
Among the solutions pre-filled RenoMac mattresses 0.30m thick was chosen.
This technique was chosen over rockfill for several reasons as it protected the bank just in the area where erosion by turbulence would occur, without having to protect the entire slope of the bank till the bottom. To ensure against the sliding stability, RenoMac mattresses were attached to a net stapled to the base and anchored at the head of the bank in a backfilled trench.
The RenoMac plus protection, being only of 0.30m thick, was largely preferred against an alternative equivalent 1.20m rip rap.
This considerably reduced the volume of material to be transported and implemented and limits the carbon footprint of the site.
RenoMac Plus mattresses are fabricated with a double diaphragm obtained by pleating the base panel. They are equipped with vertical industrial made tie rods connecting the base to the cover.
The netting is a 6x8 type double twist hexagonal mesh associated with a 2.2/3.2mm diameter wire coated with a Zn95/Al5% alloy and a high abrasion resistant polymer sheath extruded on the steel wire (PoliMac).
Lifting bars, integrated in the mattress allowing safe handling of pre-filled structures.
A suitable filter fabric is then assembled in combination with an additional wire mesh panel under the base unit, extending by 0.50m on two sides, one in the longitudinal and one in the cross direction, to ensure continuity of protection between two cages.
The Assembly and pre-filling of the units was made in an area near the work area.
The mattresses were filled mostly by mechanical means, with small manual arrangement to limit voids as much as possible. Concurrently, 2x1x1m CubiMac units were prepared on the bank.
RenoMac Plus units were installed from a barge on the Rhône. Divers assisted during launching operations to ensure exact positioning.
In conclusion, RenoMac Plus pre-filled rock mattresses have proven to be an excellent innovative solution to prevent scour protection of quay walls due to jet propellers in both cases. The suitability of their solution and the ease of installation were also important factors leading to their selection.