Continuous monitoring enables complicated work
Published 2010-06-21 00:00:00
The old railway bridge crossing the Södertälje channel had reached an age of almost 90 years. Excessive maintenance created repeated interruptions in rail traffic and cost a lot of money. The Swedish Railroad Administration therefore decided to build a new bridge. Bergsäker was given the responsibility for the extensive measurement program in a very complex terrain
The railroad crossing the Södertälje bascule bridge is today mostly used by commuter trains, but to some extent also freight trains. Approximately 190 trains are passing every 24 hours. The old bridge was not designed to meet present-day performance requirement. The bridge must carry heavier trains and enable passing of larger ships with deeper draft. Furthermore, the noise from the passing trains was very loud on the old bridge.
The new bridge is designed to handle much heavier axle loads and generate less noise. It will stretch approximately 230 metres, whereof 55 metres is above the actual waterway. During opening, the bridge will have a vertical clearance of 45.5 metres. Because the distance between the supporting pillars is increased, it will also be possible to widen the channel. The new bridge will be inaugurated during spring 2010.
The project owner and the client had decided on an extensive monitoring plan where many different parameters should be measured continuously. Bergsäker used field measuring instruments together with the AvaNet Web to measure and continuously monitor the temperature in the steel construction, air temperature, movement in the construction, air pressure, noise, vibrations and inclination as well as pore water pressure in the adjacent river bank.
The reasons for the extensive measurements are the rigorous safety requirements. This in its turn originates from the poor ground conditions at the site. The river banks are steep and very unstable. The geotechnical situation is complicated, with as much as 60 metres of clay and gravel overlaying solid rock. There is also a fault zone in the area, which was suspected to contain heavy fractured rock.
“We measured extremely many different parameters and cooperated with several of Sweden’s leading experts” explains Steffan Österberg at Bergsäker, responsible for the measuring job. “In some occasions we reached the limit of what you can do with the technique and in such situations a heavy responsibility of knowing what you are doing is resting on the shoulders of everybody involved. No doubt then it is extra encouraging hearing from the client afterwards that you have made a good job” Steffan continuous.
