References
McDermott Terminal
MEXICO, 2009
Construction of a terminal for constructing and launching offshore oil platforms
Cimesa, a Soletanche Bachy subsidiary, was assigned the execution of the McDermott Terminal in Altamira. This terminal is intended for the fabrication and launching of offshore oil platforms with a maximum weight of 10,000t. The works include the construction of a quay diaphragm wall, soil improvement by rigid inclusions, and the foundations and civil engineering works for the two launch structures.
The terminal consists of:
- Two 200 linear metre fabrication and launch structures (Corredera 1 and Corredera 2). Each Corredera has three reinforced concrete beams founded on pairs of barrettes.
- Two structures called Cabeceras, built at the end of each Corredera; they consist of reinforced concrete blocks that are 2.5m high and have a surface area of 15 x 24.3m, founded on barrettes. This very sturdy structure was built because of the major loads created by the platforms when they are launched.
- A 300 linear metre quay made of diaphragm wall (1m thick and 22m deep). Stabilisation of the diaphragm wall in the typical section is based on a level of permanent ground anchors embedded into the head of the diaphragm wall. Stabilisation of the Cabecera (headwall) section of the diaphragm wall is ensured by the Cabecera itself as well as by the beams of the Correderas (slipways) which act as passive anchors.
Works phasing
- Creation of a work platform.
- Construction of the diaphragm wall for the quay.
- Construction of the rigid inclusions (bored using a Starsol continuous flight auger) at the rear of the diaphragm wall, across a 14m-wide strip in order to limit the side pressures on the diaphragm wall and to avoid having the free length of the anchors being adversely affected by consolidation of the clay due to the new load exerted by the fill.
- Drilling and fitting the final high-capacity ground anchors.
- Construction of the capping beam.
- Tensioning of the ground anchors.
- Construction of the distribution layer over the rigid inclusions.
- Construction of the barrettes, excavated using a hydraulic grab.
- Construction of the concrete beams for the Correderas.
- Construction of the concrete blocks for the Cabeceras.
- Placement of the metal plates used as the sliding surface.
Control units were placed on 11 ground anchors in order to monitor changes in the load over time. Inclinometers were placed in the diaphragm wall in order to monitor displacement of it during works and after completion.
Techniques
Regardless of site size, and providing it involves a significant proportion of works in the ground, Soletanche Bachy will handle the complete project, and all aspects of the works, including site supervision, excavations, foundations, civil engineering and all construction operations.
A diaphragm wall is a reinforced concrete wall that is made in situ. The trench is prevented from collapsing during excavation, reinforcing and casting by the use of supporting bentonite slurry. The slurry forms a thick deposit (the cake) on the walls of the trench which balances the inward hydraulic forces and prevents water flow into the trench. A slurry made of polymers can also be used.
A ground anchor is a load transfer system designed to transfer the forces applied to it to a competent stratum. An anchor is said to be temporary if it has a lifespan of under two years and permanent if the lifespan is over two years.
Soil-improvement techniques involve changing soil characteristics by a physical action, such as vibration, or by the inclusion or mixing in the soil of a stronger material. The aim of this process is as follows:
- increase the load-bearing capacity and/or the shear strength,
- reduce both absolute and differential settlements or in certain cases, accelerate them,
- to mitigate or remove the risk of liquefaction in the event of an earthquake or major vibrations.
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