Studio geomeccanico nella conca di Sappada (Belluno): analisi di stabilità dell'area attraversata dal Rio Lech e verifica di caduta libera di massi

This paper identifies and analyses two different possible problems determined by the future realization of some ski-tracks in the Sappada area. The alternating strato of siltstone, sandstone and marl, which crop out on the slopes flanking the Lech Rio (track 01; Fig. 1), justified the determination, for each lithotype, of the ten parameters of discontinuity, later used to define the RMR, RMRc, SMR and modified GSI systems. The cross-section of such a complex stratification was obtained through the delimitation of some areas - structural regions -, distinguished by homogeneous physical and mechanical properties, though characterized by different proportions of the above mentioned lithotypes. Besides, it was traced the presence of a weathered surface portion of the rock mass, which has different strength characteristics. The stability analysis, computed through the SLOPE/W program, allowed determining minimum factors of safety and the associated critical slip surfaces. Two different strength models were employed: in the former, known as Coulomb's shear strength criterion, the cohesion and the angle of internal function were respectively obtained using Hoek's equations of 1998 and the RMR system, where the two geomechanical characteristics are conditioned by the calculation methods used; in the latter, the generalized Hoek & Brown criterion for jointed rock masses, along with the equations suggested by Balmer G. in 1952, resulted in an equivalent Mohr envelope, relating normal and shear stresses mechanically distinguishing every structural region.