28 May 2004
28 May 2004
GFRP’s rebars have been introduced by tunnelling contractors in Brussels to speed up the process of penetrating through slurry walls with Tunnel Boring Machines.
Most of the 1 million inhabitants of Brussels are without adequate treatment for water waste, which is currently disposed of in the nearby river Senne.
However, a Brussels (Belgium) based project is hoping to address this problem via the provision of a new efficient treatment system, whilst also giving rise to the building of one of the largest water treatment plants in Europe.
Pipes and collectors nearly 7 km long will be built between Brussels and the treatment plant and be dug underground at a depth of between 8 and 18 meters. The collectors will be built by a Tunnel Boring Machine (TBM) which will leave from a working shaft and arrive in the end shaft. The Diameter of the bores are between 90 and 220 cm with the working and exit/end shafts generally being rectangular shaped and built out of slurry walls.
Breaking through the reinforced slurry walls with a TBM has always been a challenge for the tunnelling contractors and engineers, generally due to slurry walls being reinforced with steel rebar cages. The TBM has previously been required to stop prematurely in order to manually cut away and remove the concrete and steel reinforcement in the slurry wall. This manual process is time consuming and creates added problems with regards to waterproofing and operator safety.
But by introducing a “Softeye” in the shaft wall, this problem has been alleviated. A “Softeye” is essentially the section of the wall through which the TBM will enter but reinforced with a “soft” type of rebar made out of Glass Fibre instead of steel.
The main purpose of the soft-eye is to allow the entrance and removal of the TBM. By using Aslan GFRP rebars, the cutting operations are simplified due to the low transversal resistance of the glass fibre materials compared with steel.
The contractors for the project, Franki Geotechnics, have selected the Belgium company, Fortius, to build the softeye with the Aslan GFRP rebars. The overall design was carried out by Co-Force International, Italy adhering to the “ Guide for the design and construction of concrete reinforced with FRP rebars” reported by ACI Committee 440 and published by the American Concrete Institute.
Aslan GFRP rebars have been used at several other tunnelling projects in Hong Kong, Bangkok , Portland, London, Los Angeles, India. They have also been deployed in area’s where temporary tension anchors or non-corrosive anchors are needed and have been known to have found a use for structural repairs in wood structures or as anchors for historical natural stone structures.
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