Back-analysis techniques for the improvement of the understanding of rock in underground constructions

In many cases, it is necessary to realize design and begin the construction of underground works with only an approximate understanding of the geomechanical parameters of the rock mass that are necessary for a correct definition of the construction technique and of the support structures. The purpose of back-analysing the measured displacements of the tunnel perimeter and the loads on the support structures during the construction of the work is to calibrate the initial estimations of the geomechanical parameters of the ground. Today the use of the back-analysis procedure is not so common and, when it is used, it does not follow a scientific scheme. Full advantage is not taken of the monitoring data, with the consequence of a waste of money. Computers are nowadays able to quickly perform many numerical analyses and therefore the time is ripe to set up a correct backanalysis procedure to use together with a calculation model of the problem, when monitoring data are available. The principles on which the treatment of information derived from the monitoring of underground works during their construction is based are shown in this paper. The paper proposes new efficient mathematical back-analysis techniques for the problem under consideration and some interesting examples. Finally, a real case is presented to which back-analysis was applied.