During the construction phase of a tunnel, the excavated area tends to “shrink” (convergence) during the hours/days after the digging. If the convergence is excessive, this implies an elevated risk to the stability of the construction work.

Currently, in order to verify the inexistence of convergence issues, two manual methods are used. However, both systems require a large number of staff and the measurements to be done daily. On top of this, the excavated section of the tunnel must be circular but with irregular finishing, thus an added difficulty.