TDEP Phase 2 Quayside Development

This project is to extend the already completed Phase 1 section of the quay which is currently been used by the Equinor SOV. The TDEP site is currently the operational and maintenance base for the windfarm with a permanent facility employing up to 150 people.

The existing quayside consists of an existing dilapidated jetty and a concrete suspended quay which extends from a quay top level of approximately +6.60m CD (+4.00m OD) down to the riverbed at a depth of about -6m to -7m CD, so a retained height of between 12 to 13.5m. The riverbed in this area consists of soft alluvium and silt overlying alternating layers of strong sandstone, mudstone and siltstone bedrock of the carboniferous coal series which is relatively shallow (-10.00m CD). The existing quay structures along the section are old and is approaching the end of its serviceable life due to sub-aerial corrosion, marine corrosion and accelerated low water corrosion of the steel sheet piles.

The proposed wall in this contract continues from the end of Phase 1 section along the remainder of the quay up to near the former graving dock entrance, a distance of 90m. The Phase 1 works is the initial 122m length from the existing wall at the South end of the site. To ensure a straight berthing line for shipping, the 2.6m offset distance will be retained although this does reduce in places due to the variation in the alignment of the existing wall. It is envisaged that the new quay wall will be of a similar construction to that installed in the Phase 1 section, consisting of a steel combi-wall tied back at the top with anchor rods to an anchorage system located in the ground approximately 25m to the rear. A reinforced concrete cope will connect the tops of the piles together to form a continuous hard edge to the quay front. A shorter length of anchor ties will be utilised where the wall will be installed adjacent to existing suspended deck structure.

The current dredge depth varies from -6m to -7m CD. The quay is to be designed for a future dredge depth of -10m CD. Due to the high level of the sandstone bedrock, spigots will be required, or the piles will have to be cored through the sandstone to achieve the necessary toe depth to ensure stability when the berth is dredged to the -10m CD depth in the future and to prevent undermining from scour.

The quay will be fitted out as part of the works with new bollards, fenders, ladders, grab chains and hand railing as shown on the drawings. Provision will also be made for quay side services (installed by others) and drainage. New concrete surfacing and topping will be installed to the rear to facilitate drainage, some of this will be new ground slabs which will be piled to reduce the loading on the new quay wall from the proposed applied ground surcharge loading of 10tonnes/m2.

The existing ground contains a number of relic structures from the previous use of the site including disused jetty, building foundations, bollard foundations, dock closure walls. There is also a suspended slab which is a piled structure located towards the end of the works. The supplementary information provided with the tender documents contains archive drawings of the Phase one works and other historical records relating to the quay side. The tenderer is to consider this information when designing and positioning the new quay, anchorage system and all piles to make due allowance for these old structures.

The Equinor SOV currently using the TDEP Phase 1 berth will be visiting the site twice a week and be in berth for 12 to 24 hours. Contractor shall take this into consideration in pricing the job.