Construction of the first phase of HIT 2 related to the building of a bund projecting from the seawall adjacent to the Immingham gas jetty, in a curve to the proposed jetty face and extended to meet up with the existing HIT1 bund.

ABP departed from established practice by using in-house resources to construct the first phase. A team comprised of Immingham's engineering staff and ABP's dredging subsidiary, UK Dredging (UKD), was established. This team was responsible for concluding the detailed design with CL Associates, ensuring an optimal design combined with the lowest achievable cost. UKD took on the role of principal contractor, arranged all necessary support contractors and was responsible for the health and safety aspects of construction.

The final design of the bund required some 70,000m 3of erodable material be removed from the foreshore and a trench dredged (45,000m 3) to provide a suitable foundation for the bund.

The trench was partially filled with sand, providing a base for chalk infill.

To reduce tidal delays for dredging plant, the foreshore was first lowered by ploughing. The material was moved to a berthing pocket partially dredged during HIT1 works and subsequently removed to a disposal site by a trailing suction hopper dredger (TSHD).

Humber Work Boats was then engaged to cut and dredge the bund pocket. The cutter suction dredger (CSO) John M worked from deep water to shallow water cutting to design profiles. The dredged material was discharged via a 200mm floating pipeline to the berthing pocket where it was re-dredged by UKD's TSHD UKD Marlin. Effective scheduling of the CSD and TSHD minimised down time. When the John M was not working, the UKD Marlin was redeployed to other maintenance dredging commitments.

Once the bund trench was cut, infilling with sand began. The John M was replaced by the spread pontoon 'Rebecca M'.

A 600mm diameter floating pipeline pre-constructed at Grimsby Dock was towed into position and connected to the spread pontoon at the nearshore end of the trench. The mooring barge Mortlift was placed strategically at the seaward end to provide a mooring platform for sand discharge from the dredger.

Positioning and mooring arrangements were critical so as not to restrict commercial activities on adjacent jetties or interfere with navigation channels, all while holding the sand discharge vessel in strong tidal currents. The mooring vessel included a crane to facilitate hose handling operations.

The UKD Marlin made beneficial use of sand won from maintenance dredging at the Sunk Dredge Channel, delivering it to HIT 2. With discharge pipes on both sides, the vessel was not restricted by tide and pumped the sand some 500m to the discharge point. A prefabricated diffuser controlled the discharge to maintain design levels, with sand placed to a depth of 4m over the width of the trench.

Chalk backfilling to create the bund commenced as soon as possible to ensure that sand was not removed by tidal flows and design footings were maintained.

The programme of sand delivery and placement and chalk backfilling was thus closely programmed and monitored.

This phase of the works was completed in January.

MJ Information No: 17015