ALBERT

Description: 〈span〉〈div〉ABSTRACT〈/div〉This work describes and analyses the December 2004 rockslide that affected the working face of the Ca’ Madonna quarry (Municipality of Urbania, Province of Pesaro and Urbino, Italy), where limestones are extensively quarried for aggregates. The landslide occurred along an unsurveyed, approximately 10-cm thick clayey intra-bed layer that mainly consists of smectite-group clayey minerals. Laboratory analyses indicate that it is very active and shows a high capacity to absorb water until reaching a swelling pressure of up to 1200 kPa. Mining activities reduced lithostatic load and facilitated rainwater infiltration down to this bentonitic layer, which led to fully softened conditions with a resulting severe reduction in the shear strength parameters. Under such conditions, the slope stability back-analysis was performed by the limit equilibrium method, considering a planar rock slope failure with tension cracks and with different water level heights. The results show that a small increase of water pressure was sufficient to exceed the factor of safety. Stratigraphically, this layer can be correlated with the Lower Campanian Bentonitic Layer already reported in other sites of Central Italy. Therefore, the potentially great spatial extent of this layer and the possibility that the reported conditions may occur in other similar settings, make it important to identify its presence in order to prevent analogous situations.〈/span〉

Description: 〈span〉〈div〉ABSTRACT〈/div〉Many buildings of the historical centre of Urbino (Marche, Central Italy), included in the UNESCO World Heritage List, are characterized by portals consisting of sedimentary rocks such as limestones or sandstones. In order to identify the possible quarries of provenance of sandstones used for architecture, we addressed our research to the Sant’Ippolito area (20 km ESE of Urbino), where historical stonemasons have been extensively documented since the 14th century. Few traces of ancient exploitation indicate some extraction sites. All the investigated rocks (both from monumental portals of Urbino and geological outcrops) consist of fine- to medium-grained sandstones with a variable content of bioclasts. Two different groups were recognized (using the petrographic Q-F-R classification diagram): (i) lithic arenites belonging to the Colombacci Formation; and (ii) feldspathic lithic arenites referable to the Tripoli Unit. In particular, petrographic data indicate that the sandstones used in the historical buildings of Urbino, come from the arenitic lithofacies of the Messinian 〈span〉p.p.〈/span〉 Colombacci Formation of the Sant’Ippolito area. In addition, comparative geochemical studies of whole rock major and trace elements point out three outcrops of the above formation, as possible sites of ancient extraction. Sandstones of the Tripoli Unit and the Marnoso-Arenacea Formation, widespread in the study area and near Urbino respectively, are ruled out as source rocks, based on both petrographic and geochemical data.Anomalously high values of some heavy elements such as Pb, Zn and As, recognized in some of the portals, likely derive from a combination of various anthropogenic sources of pollution close to the investigated monuments, such as domestic heating and emissions from road traffic in the past.From a mechanical point of view, the uniaxial compressive strength tests, carried out on a representative number of selected samples of the Colombacci Formation lithic arenites, yelded low values and high variability. Other investigated physical parameters also indicate that the stones used for the portals did not represent a good choice as building material. This implies that the stonemasons of Sant’Ippolito chose local raw materials for their availability, aesthetic qualities and good workability, rather than structural properties.〈/span〉