No time for error

Chapter 2: Ensuring a smooth shift

No time for error

Ensuring a smooth shift

Planning for the shift, SCP Bertheau Saint-Criq had to ensure when the bridge was lifted that its 8,000 tonnes wouldn’t sag and risk breakage. To do this, the firm conducted a preliminary as-built survey of the structure to verity that it was built to plan specifications. Also, the surveyors needed to ensure the concrete slab the bridge rested upon hadn’t moved during the nine months of construction and the batteries axes were in alignment with the planned trajectory of the shift.

During this first phase, SCP Bertheau Saint-Criq used the Leica Viva TS15 targeted to 10 Leica GMP104 prisms set up on the bridge piers. With the high accuracy and dedicated lock-on capabilities of the total station, the firm was able to accurately verify the integrity of the structure and calculate the bridge’s final position.

Another concern the firm had to address was the capability of the cylinders that would guide the actual shift. Two cylinders per line would push 1,000 tonnes each. The cylinders would act in parallel to ensure the direction of the skid as it is essential to avoid an offset, which can cause a blockage.

In the next phase, the actual shifting, the Leica TS15 was set up on a concrete pillar and six prisms were fixed on known points, consistently retargeted to the total station to account for temperature and humidity changes. These adjustments allowed SCP Bertheau Saint-Criq to avoid costly errors that would have thrown off the entire schedule, causing the whole project to fail.

The shifting was a slow process, moving only 5m every hour. With the precise calculations provided by the monitoring solutions of the total station and prisms, the firm was easily able to predict how far the bridge would move.

Far less easy for the surveyors was determining how the structure would react to the actual shift due to angle and weight. The greatest fear was the structure breaking and nose-diving into the gorge below.

“Confidence in the accuracy of measurements and the material used is paramount. Especially when the results do not match the expectations of different stakeholders and can be challenged. It is then important to quickly prove the reliability of what is ahead,” said Nicolas Bazerque, the SCP Bertheau Saint-Criq surveyor in charge of the project.

Explore next chapter: Automating for accuracy

Story: No time for error
Chapter 1: A long working weekend
Chapter 2: Ensuring a smooth shift
Chapter 3: Automating for accuracy

Reporter 74 - May 2016

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