FinMeas automatic extensometers – the tool of choice for the Rantatunneli Alliance project in Tampere
Measurement technology developed by FinMeas was used in highway tunnel construction work in Tampere, Finland. FinMeas automatic extensometers were used to monitor rock bed movements throughout the tunnel construction project, which took several years.
The client was Tampere Rantatunneli Alliance, whose partner responsible for rock engineering was consulting engineering firm Saanio & Riekkola Oy. Excavation work on the 2.3-kilometre highway tunnel began in spring 2014 with a scheduled completion date of 2017.
“In many locations, the excavation and blast sites for the Rantatunneli were located directly below buildings, which made careful rock engineering vitally important,” says Kari Äikäs, Project Manager at Saanio & Riekkola Oy.
Construction work that involves rock engineering usually includes the monitoring of vibrations caused by blasting and drilling, groundwater surface levels, possible subsidence affecting buildings and structures, and rock movements. Inside the Rantatunneli tunnel, FinMeas extensometers were used to monitor vertical movements in the rock at five measurement points.
Rock is usually subject to an area-specific level of stress, to which excavation work causes changes around the excavated cavity. During excavation work, such stress causes the walls of the tunnel to move inwards and the roof to rise. Movement of this kind is measured in millimetres.
“This type of movement is normal. We have used modelling to anticipate rock behaviour and conducted measurements to verify the reliability of our modelling. If there is more than a few millimetres of such movement, this means that our calculations are incorrect and the rock may be affected by unforeseen risk factors,” Äikäs explains.
“If the movements are minor, all is well. However, if the measurements indicate movement that is more substantial than anticipated, people at the construction site can react quickly and, if necessary, add more reinforcement structures, for example.”