Ramboll’s detailed design for a major upgrade of Morocco’s Jorf Lasfar facilities is being implemented while the port remains operational.
The industrial port of Jorf Lasfar in Morocco is undergoing major rehabilitation and extension works, facilitated by Ramboll’s detailed engineering design. The 190-hectare site opened in 1982 with berths for exporting phosphates, fertilisers, coal, chemicals and bulk products. To keep pace with the anticipated rise in demand the current project is working on seven quays. It consists of upgrading existing quays and constructing new ones, made more interesting by the construction and logistical challenges of keeping the port fully operational.
Ramboll is working with the engineering, procurement and construction contractor Archirodon, and providing complete detailed design for all the remedial, rebuilding and new works at Jorf Lasfar. Our services here encompass geotechnical, civil, infrastructure, marine, mechanical and electrical engineering. Technical experts from our UK and Denmark offices are involved with all aspects of the project.
Geotechnical investigation enabled us to develop a ground model of the layered geology of marls, sandstone and limestone before commencing the detailed design. The client originally envisaged precast concrete caissons throughout the scheme. However, the contractor’s tender proposal of diaphragm walls in combination with caissons was accepted as a time-efficient solution.
Three quays are being constructed using diaphragm walls and tie-back piles and two quays are being extended with caissons. Upgrade work to two more quays is limited to rehabilitating existing structures and deepening their berths by dredging. Some quay extension work on the landward side of existing quays replaces earth embankment access roads, and is being constructed in areas of fill and pre-existing material, further complicating the engineering design details.
Cost-effective circular precast concrete caissons with cast in-situ fairing panels were selected to produce the required flat faced quays, and a floating dry dock was brought to site specifically for casting. The caissons, 15m in diameter and 20-22.2m high, are floated and sunk into position to form a gravity wall. Ramboll used Plaxis 2D and 3D digital modelling to analyse the caisson design. Concerns about possible caisson overturning in soft marl were overcome by dig and replace ground improvement.
Concrete diaphragm walls up to 400m long and 34m deep are toed into resistant marl or limestone bedrock. Changing geology along the walls is accommodated in the design by changing the reinforcement rather than wall depth.
The walls are formed using a hydrofraise, making panels 1.2m thick and 2.4-2.6m wide. The centre of each panel is anchored by an inclined steel tie rod to a 1.2m diameter 25m long bored cast in-situ pile behind the wall. Connections with the piles are below sea level (4m below ground) to limit pile bending moments. Diaphragm wall configuration and pile positions are dictated by the rails being installed to support the dock cranes running along the quays.
Rehabilitation of existing concrete structures required careful inspection and concrete testing to chart the necessary repair work. The original concrete caissons had deteriorated and reinforcement had corroded owing to relatively high ambient temperatures, exposure to the marine environment and chemical attack. We assessed their durability meticulously and specified efficient remedial action, the implementation of which ensures the repaired structures meet their required design life. Phased construction work is allowing ongoing port operations.