References

Genk central lock

BELGIUM, 2007

Rehabilitation of a river lock

Genk's Albert Canal lock system comprises 2 locks of 150m in length (northern and central locks) and a third lock 200m long (southern lock). The central lock had suffered considerably from erosion, which had caused subsidence and significant cracking in the base slab and the side walls. The lock was taken out of service. With the expected increase in traffic in barge-borne containers between Antwerp and Liège, the local Department of Navigable Waterways decided to bring the central lock back into operation. Rehabilitation works were necessary to stabilize the lock structure. Soletanche Bachy and its subsidiary, Fontec, were chosen as general contractors for the job.



The lock was stabilized mainly through jet grouting work under the lock and by prestressing the side-walls, in the following stages:
- Drilling through the concrete structure using a Down The Hole (DTH) hammer.
- Grouting of voids and cracks in the structure and compaction grouting of compressible soil.
- Upstream cut-off of the groundwater circulation under the structure by installing a watertight curtain made of secant jet grouting columns 1,600mm in diameter.
- Jet grouting columns (double jet method) of Ø 800mm to Ø 1,200mm underpinning the lock structure.
- Vertical ground anchors (377kN) for prestressing the side walls and horizontal and subhorizontal anchors (300kN to 710kN).
- Minor civil engineering work for reinforcing the angles between the slab and the side-walls.

With the ground water exerting 10 to 12m of pressure on the slab, the structure was dewatered (300m³/hr.) before the jet grouting operation under the slab, to avoid having to work using an airlock.

The North and South locks remained in operation throughout the stabilisation work.

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Techniques

Civil engineering

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.

Grouting

Grouting involves the injection of a pumpable product (slurry), which will subsequently stiffen, into the soil or into man-made material (masonry), in order to consolidate the soil or structure or make it impermeable, through filling all the voids it contains. The slurry can fill the voids in the ground, the cracks within rock, solution cavities (it is then referred to as fissure and permeation grouting) and/or displace the surrounding soils through a bottom-up process or by fracturing (compaction grouting or solid injection - see the section on the subject - and strain injection). Grouting with soil displacement may be used to prevent potential damage to the structure brought about by excavations (galleries and tunnels, major urban excavations, etc.) and this is called compensation grouting (see the relevant section).

Jet grouting

Jet grouting is a construction process that uses a high-pressure jet of fluid (generally 20 – 40 MPa) to break up and loosen the soil at depth in a borehole and to mix it with a self-hardening grout to form columns, panels and other structures in the ground. The parameters for the jet-grouting process and the desired final strength of the treated soil depend on a number of characteristics, such as the soil type, the technique used and the objective to be reached. In granular soils, the high-pressure jet breaks up the grains through erosion, while in a cohesive soil, such as clay, the jet breaks the mass up into small particles. High pressure is needed to produce the kinetic energy required for the jet through a small-diameter nozzle. Waste material from the process (a mix of soil, water and binder) is recovered at the surface before being taken away for disposal.

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