On March 3rd 2009, Cologne’s Historical Archive building suddenly collapsed, taking a thousand years of public records with it. Two residents of the neighbouring apartment buildings, also destroyed in the disaster, were killed. Water seepage into a tunnel being built for an underground railway line was blamed for weakening the foundations of the buildings.
The Cologne disaster demonstrated that tunnelling projects cannot completely avoid risk, but Klaus Chmelina wants to reduce it. Chmelina is the R&D Manager at Geodata, an Austrian SME which supplies IT systems for underground construction. Geodata, together with Institute for Structural Mechanics of the Ruhr-University Bochum and the Mining University of Leoben participated in Eurostars EMSAT. The objective of the project was to make tunnelling safer by using real-time monitoring data from tunnel boring machines to make accurate predictions about the excavation process.
A tunnel boring machine, or TBM, is a huge cylinder of metal of up to 19 meters in diameter. It is used to excavate large tunnels. “Today they are used for almost every kind of project of at least a few kilometres in length,” says Chmelina. Tunnelling projects are becoming more complex and difficult. “If you think about urban tunnelling where metros or subways are being built they are quite close to the surface,” says Chmelina, “In some cases there is just a meter until you reach, let’s say, the cellar of a house.” The deformation of the ground caused by the TBM can cause the structures above ground to sink or even collapse.
A NEW APPROACH
Excavation projects often use simulations during the design phase to predict safety risks like ground collapses and cracking, based on estimates of the stresses and pressures in the ground. However, during construction itself, engineers still rely on manual interpretation of geotechnical measurements and the monitoring data from the TBM itself.
A modern TBM measures up to 100 parameters per second. EMSAT developed a system which feeds that data into a simulation. “From this data can be prognosed the displacement or deformation of the ground, and of the surface above the ground, if the tunnel boring machine continues,” says Chmelina. “This can be predicted for let’s say 20 or 40 meters in advance.”
"A tunnel boring machine, or TBM, is a huge cylinder of metal of up to 19 meters in diameter."
In other words EMSAT’s system lets engineers see into the future, based on the true conditions during excavation, and take appropriate action to reduce risks. “For example you are approaching a house, it can tell you that if you continue with that force, speed, etc. then that house will have a settlement of 1cm,” Chmelina explains. “I can reduce the excavation speed and if I do, I’ll immediately get a new prognosis telling me that the settlement will now only be 7mm.”
EMSAT’s system has been tested using data from four real tunnel projects, including subway projects in Copenhagen and Thessaloniki. Simulations were conducted as if the tunnel was under excavation and compared with the true results. “We were close by about 3-5mm,” says Chmelina.