Case Studies

Tighter tolerances for tunnel longevity

Tighter tolerances for tunnel longevity

Tighter tolerances for tunnel longevity

French mould specialists CBE are helping their customers to produce more accurate concrete segment moulds that reduce construction challenges and enhance life expectancy of tunnel linings.

Advances in tunnel technology are increasing the viability of tunnel projects to solve infrastructural challenges all over the world: from reducing congestion in megacities to opening access to remote valleys.

Precast concrete segments allow tunnel constructors to reinforce the tunnel quickly and cost-effectively. The CBE Group is a leader in this field, making concrete segment moulds and all associated handling equipment for customers on five continents.

“We know how to integrate the production of the precast segments into the overall tunnel boring process so that work can proceed smoothly and without complications,” says CBE’s CEO Pascal Clerc. “Any inaccuracies in the geometry or dimensions of the segment will lead to delays or problems during the tunnel construction phase or issues of reliability during the tunnel lifetime. For example, if the segment surfaces don’t match precisely, stress cracks may result. Also you might have problems with water leakage between segments. That is why we make moulds that are accurate to +/- 0.3 mm. This level of accuracy sets us apart in the market.”

Founded over 25 years ago, CBE has played an important role in the evolution of technology and methods in this field. “Staying ahead of the game is all about recognising the trends and working out what technology and methods are needed to fulfil the expectations of the customers.”

A FARO Laser Tracker ION® is used to verify the dimensions and geometry of all the contact surfaces of the mould. “Before we had the FARO Laser Tracker we had to rely on templates for quality control. Our measurements were limited to 2D and deviations could easily go unnoticed. With the ION, we not only save time and increase the accuracy – we are able to verify any point on the mould with respect to the CAD files. This ensures that the geometry and longevity of the tunnel will not be compromised.”

“We evaluated 3 types of laser tracker and chose the FARO product based on the combination of price, performance and service,” explained Mr. Clerc. CBE’s current production capacity is 2,000 moulds per year and the dimensions of each mould can be verified with the FARO Laser Tracker ION after manufacturing in a batch process. “We use it in a raw workshop climate, so having a robust, mobile and easy to use solution was vital.”

Besides the moulds, CBE makes all the associated handling equipment including fully-automated moulding plants with outputs of 5 to 6 segments per hour. CBE’s engineering office works closely with the tunnel engineers to optimise the design of individual segments and of the segment precast plant. “The more accuracy we can offer, the more customers appreciate the advantages of precision. We now have a new customer in the Netherlands that requires a tolerance of +/- 0.2 mm.”

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