Connecting continents

The third bridge above the Bosphorus, with its over 300 metre high pylons pairs, is a monumental masterpiece of engineering. It will help to reduce traffic between the Europe and Asian continents and is equally a symbol of Istanbul’s prosperity and economic growth. The Yavuz-Sultan-Selim Bridge is being built by the Turkish company, ICA Construction, and creates not only a motorway with a railway line, but also an additional connection for the transcontinental metropolis between the two continents. During the construction of the suspension bridge, the Leica Nova MS50 demonstrated its many diversified application possibilities.

ICA utilised the Leica Nova MS50 MultiStation, along with the Leica Viva GS15 GNSS receiver and other additional Leica Geosystems sensors, during construction for a great number of surveying, control and deformation measurements. With the new scanning function, the latest construction progress of the pylons could be compared with the architectural plans.

The highest bridge pylons in bridge construction
Four huge pylons connect the substructure of this bridge. With a height of 309 metres (approx. 1014 feet), they are the highest found on any suspension bridge worldwide. The two obliquely designed pylon pairs complete the top of the bridge and are hollow inside. Every day, these pylons grow approximately 2,5 metres (8,2 feet) – a challenge for the engineers, who must constantly check for deviations from the design of the ever-growing outer concrete shells of the pylons. Due to stringent demands of the construction requirements, there is only a short period of time available to check the pylons, nevertheless, these controls are absolutely imperative. Because any small deviation from the design would have an enormous impact on the subsequent stages of the bridge construction.

The laser scanning function and long range measurement of the Leica Nova MS50 was used to determine the concrete surface deviations against the design and was processed with Leica Cyclone point cloud software. To achieve the highest accuracy of the scanned data, the MS50 was set up over control points established using Leica Viva GS15 GNSS static observations and processed in Leica GeoOffice.

An additional challenge was the harsh environment in which this work was carried out. The Bosphorus Strait connects the Black Sea to the Marmara Sea and workers have to contend with a cold northernly wind, together with haze and humidity, which can persist throughout the winter months. All Leica equipment that was used for this project could easily cope with these challenging conditions. The Leica Nova MS50 has a working temperature range of –20°C to + 50°C and IP65 dust and water protection.

High-quality measurements
Most of the work was carried out from three ground control points. Two were located on nearby hills to offer a clear line of sight to the pylons and construction site and the displacement control was carried out on a weekly basis to check if the coordinates were stable and to compare with the architectural designs for deviations.

In addition, vertical alignments of the pylons were checked using several Leica TS30 total stations. Measurements were taken during construction from different positions in order to verify the accuracy in real time of as-built plans.

The Nova MS50 was set up over the control points, a scan window defined and a point cloud measured with a density of 1 cm every 100 m over a distance of 150 m. After collecting scan data from all sides of the pylons, vertical slices, created in Leica MultiWorx were checked against the design (CAD) data.

Fast and accurate scans
Surveying manager Yasar Hacieyupoglu commented, “We had complete confidence in the Leica Nova MS50 and Viva GS15 GNSS receivers to deliver the accurate long range measurement required for this project. The Nova MS50 is the only instrument which can scan accurately and at speed over the range required.”

“Leica Geosystems has been a collaborative partner on this project – the construction company ICA, the main contractor, HYUNDAI Eng. and the surveying team, ENDEM Cons all use Leica Geosystems’ products and know they can count on the support, training and service they receive from the manufacturer and market leader.”

Written by Ruth Badley