Geotechnical Characterization and Stability of a Slope in the Marnoso-Arenacea Formation for the Realization of an Underground Car Park in Urbino (Italy).

The plan of an underground car park located near the historical centre of Urbino town, has required to characterize the Marnoso-arenacea Formation (Tortonian), from a geomechanical point of view. The project implies that the intervention will be insert inside the flank of the hill, in order to mitigate the effect of the environmental impact. It also involves an excavation front 42 m high and 100 m large. To analyze the mechanical behaviour of the soils, many samples both from the Marnoso-arenacea Formation and from the cover, have been tested in laboratory. The anisotropy index evaluated by point load test in natural water conditions shows a higher value of the arenitic levels in comparison with the marls. On the contrary, the marls level tested in dry condition provides greater anisotropy index data. In the monoassial compression test the arenaceous sediments show higher results. Stability analysis has shown the slope to be stable under the imposed conditions, thus confirming the assigned parameters accuracy. To sum up, stability analyses results clearly emphasized the feasibility of the project on condition that reinforcement works were made to contain the upper part of the excavation front; it is also important for it to be terraced by means of a horizontal bench in order to contain the step height within 20 m. The stability analysis carried out with distinct element method shows the opportunity to retain the upper part of the cut with anchored bulkhead.