Innovation showcase | Fast track quay wall design and construction for Ras Al-Khair Shipyard in Saudi Arabia

This mega shipyard project is part of Saudi Arabia’s Vision 2030 to diversify the economy from the energy sector. It has been developed by Saudi Aramco with technical design support from Royal HaskoningDHV (RHDHV) since its inception in 2014.

The shipyard will build and repair the full range of ship sizes from very large crude carrier (VLCC) oil tankers 330m long by 60m wide, to 60m long by 15m offshore service vessels (OSVs) as well as jack-up rigs 90m long by 89m wide. It will also have facilities for building the full range of offshore fabrications.

Accordingly, in addition to the quay walls the shipyard’s infrastructure includes a pair of shipbuilding dry docks, one 550m by 75m and the other 400m by 75m; a 374m by 90m ship and jack-up repair dry dock; a shiplift capable of lifting ships up to 250m long and with a maximum beam of 44m; plus ship outfitting and repair piers totalling 1.04km in length. Throughout the design, consideration has been given to minimising the carbon footprint of the project.

The project has a fast track programme with the aim of having the whole 1,125ha shipyard constructed and fully operational by 2024. The first production zone is due to start operations before the end of 2022. To achieve this, a two stage procurement strategy was adopted. The already completed first stage is the harbour creation and reclamation work which was done to a detailed design by RHDHV. This includes most of the shipyard’s quay walls.

The second stage was tendered on a front end engineering design prepared by RHDHV and is being constructed using an engineering, procurement and construction (EPC) contract. This EPC contract covers all landside shipyard facilities plus the dry docks, piers and the shiplift. Great care was taken in the planning of the shipyard layout to ensure that sufficient construction space was provided to enable the economic construction of the dry docks. The interfaces between the first and second stage construction contracts also required very careful planning, in particular the quay walls at the dry dock entrances.

The planned operational usage of the quay walls varies greatly. To avoid multiple changes in the type of construction method, which would have inherently extended the construction programme, two fundamental types of wall were designed. Depending on the operational requirements of the shipyard, additional load capacity enhancing features were added as needed, for example for very large crawler cranes.

The two forms of quay wall construction were determined by the existing topography and bathymetry. Where construction could be on land, secant piles were selected, but where construction had to be “in the wet” concrete blocks were adopted. The predominant ground conditions across the site are superficial deposits of calcareous sands of varying density with occasional bands of calcarenite (caprock), overlying weak calcareous sandstone and siltstone at approximately 20m below chart datum (CD).

Concrete block walls

The block quay wall structure comprises precast concrete blocks of which 15,773 were cast and placed in the first construction contract. The block walls interface level with the EPC contract for the second stage landside works was at 2.5m above CD thus enabling the EPC contractor to complete the construction of the walls’ capping beam in the dry. The typical design dredge level for the block walls is 11m below CD.

The foundation material on the seabed is sand, which was subjected to vibro-compaction where necessary to achieve the required design density along the length of the wall. Controlling the settlement of the wall was a key design factor. A 13.5m wide foundation trench was dredged to 14.5m below CD. A 1m thick rock foundation filter layer formed of 2mm to 20mm diameter aggregate was placed, overlain by a 1.35m thick rock foundation bund layer formed using 50mm to 150mm aggregates and was completed with a 150mm thick bedding layer formed from 30mm to 50mm sized aggregates The specified tolerance for the surface of the bedding layer was plus or minus 25mm. Typically, the actual variation achieved was well within the tolerance limit. Seven layers of precast blocks each weighing up to 75t were then placed with staggered vertical joints to provide longitudinal structural continuity. During the 19 month block placement programme, contractors were able to place a maximum of 97 blocks per day at the construction peak. 

The design of the wall cross section was optimised by leaning it back towards the land, which meant that the crushed rock backfill formed from 40mm to 100mm sized aggregates was placed in lifts as the blocks were placed to maintain stability.

To prevent subsequently backfilled sand from migrating into the crushed rock backfill, a geotextile barrier was placed at the interface. In the dredged trench at the toe of the wall a 1m thick scour protection layer comprising rock weighing 60kg to 300kg  was provided up to the design dredge level.

The capping beam structure is now being added to each length of quay wall by the EPC contractor according to the operational requirements for that particular location.

A major challenge at the Ras Al-Khair location is high ambient temperatures and the potential for early age thermal cracking in the mass concrete blocks. This was solved by developing a temperature control plan and detailed specification for concrete transportation, placing and curing.

The peak hydration temperature was recorded in all blocks and where the readings exceeded 70°C, additional core tests and ultrasonic pulse echo scanning were carried out to reduce the number of rejected blocks. Rejected blocks were recycled within the yard for other construction works requiring less stringent quality requirements.

At the dry dock entrances the block walls terminate at a sufficient distance from the dry docks to provide the EPC contractor with enough working space to construct the reinforced concrete entrance works including the dock dewatering pumphouses “in the dry”. Another factor determining the termination point is the presence of the temporary cofferdams at the entrance which are necessary to keep the dry dock excavations dry during construction.

The EPC contractor will carefully sequence the completion of the quay walls up to the sides of the dry docks’ entrance works following the removal of the temporary cofferdams.

Secant pile walls

The 1.14km linear length of secant pile wall is located at the waterfront of the offshore fabrication and jack-up building zones for load outs onto barges and heavy-lift ships. This quay wall is designed to provide maximum operational flexibility enabling loadouts anywhere along the full length of the wall.

Doing so removes the constraint suffered by most offshore fabrication yards of having to arrange and programme their landside production work to enable loadout at a single location at the waterfront. The design can accommodate loads of 40t/m² to 70t/m².

To enable the quay wall to accommodate the onerous combination of the high imposed loading and the design dredged depth of 12m below CD, the wall has been anchored using 140mm diameter tie rods at 2.1m centres connected to a row of bored anchor piles. For the most intensely loaded length of the quay wall a buried relieving platform with vertical bearing piles is incorporated in the structure.

The total number of bored secant piles is 2,412. The reinforcement in the piles and capping beam structures is epoxy coated to maximise the life of the structure by protecting it from the marine environment.

Published in association with Saudi Aramco and Royal HaskoningDHV

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