ABSTRACT

Rock weathering is a phenomenon that induces an increase in porosity and a partial or complete loss of cohesive strength. In most cases, especially for very hard rocks, weathering develops on a geological time scale. In some cases, however, the weathering rate can be surprisingly fast, so that mechanical properties of the rock are degraded in times relevant for engineering purposes. The practical case that is considered in this paper is related to the series of surface collapses that occurred in the Lorraine (France) iron basin in due to weathering of rock pillars of abandoned mines (see Section 3). The phenomenon is investigated by means of continuous (FEM) and discontinuous (DEM) models. Finite Element analyses are based upon a suitably conceived constitutive model of the mechanical behavior of soft rocks exposed to weathering. Distinct Element analyses are performed with the code PFC3D. The parameters of the constitutive model and those of the DEM model are calibrated on the basis of selected test performed on artificial soft-rock. In the last part of the paper, the subsidence induced by degradation of pillars in abandoned mines is studied, with both models.