A Procedure for determining the reaction curve of shotcrete lining considering transient conditions

The mechanical behaviour of a shotcrete lining is analysed in this paper using the convergence-confinement approach. A calculation procedure is presented which is able to provide the reaction curve of a lining with increasing sti¤ness, by taking into account the variability due to time of the shotcrete sti¤ness and strength, as well as the face advancement rate. The proposed procedure is also able to provide the change of the safety factor of the lining in time. This results to be a very useful tool for understanding the behaviour of this widely used support and for assigning its thickness to guarantee stability (also in transient conditions), with a known safety factor, during tunnel excavation.