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13 14Over last decade geomatic techniques have been increasingly used for the geometrical 15 characterization of rock slopes. Terrestrial laser scanning and digital terrestrial photogrammetry in 16 particular are now frequently used in the characterization of joint surfaces and slope geometry. 17Although the use of these techniques for the structural characterization of slopes is widely 18 documented, limited research has been undertaken to improve our understanding of the importance of 19 the derived data quality in the construction of slope geometry imported into 3D numerical models. One 20 of the most common problems encountered in the use of these techniques, especially in case of 21 slopes with complex geometry, is the presence of occlusions. In this context, the aims of this paper 22 are to describe how the integrated use of terrestrial laser scanning, digital terrestrial photogrammetry 23 and topographic surveys can mitigate the influence of occlusions and how the slope geometry gained 24 from these surveys can be important in slope stability analyses. For this purpose a case study in the 25Monte Altissimo area (Apuan Alps, Italy) will be presented. Several geomatic techniques were used for 26 studying a slope overhanging the Granolesa quarry. Special emphasis will be given to the importance 27 of using Total Station and Differential GPS surveys as tools for data fusion. Moreover, in order to 28 validate this procedure, the accuracy and precision of the output were determined through comparison 29 of 3D models derived from laser scanning and digital terrestrial photogrammetry. 30Furthermore, two different analyses with the three-dimensional distinct element code, 3DEC, were 31 carried out in order to highlight the advantages and limitations of using data obtained from terrestrial 32 remote sensing techniques as opposed to models based on topographic maps. 33 34 Key words: terrestrial laser scanning; digital terrestrial photogrammetry; intersection method; rock 35 slope stability; 3D-distinct element models. 36 37 Introduction 38

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Landslides of the lateral spreading type, involving brittle geological units overlying ductile terrains, are a common occurrence in the sandstone and limestone plateaux of the northern Apennines of Italy. The edges of these plateaux are often the location of rapid landslide phenomena, such as rock slides, rock falls and topples. In this paper we present a back-analysis of a recent landslide (February 2014), involving the north-eastern sector of the San Leo rock slab (northern Apennines, Emilia-Romagna Region) which is a representative example of this type of phenomena. The aquifer hosted in the fractured slab, due to its relatively higher secondary permeability in comparison to the lower clayey units leads to the development of perennial and ephemeral springs at the contact between the two units. The related piping erosion phenomena, together with slope processes in the clayshales have led to the progressive undermining of the slab, eventually predisposing large-scale landslides. Stability analyses were conducted coupling Terrestrial Laser Scanning (TLS) and Distinct Element Methods (DEMs). TLS point clouds were analyzed to determine the pre-and post-failure geometry, the extension of the detachment area and the joint network characteristics. The block dimensions in the landslide deposit were mapped and used to infer the spacing of the discontinuities for insertion into the numerical model. Threedimensional distinct element simulations were conducted, with and without undermining of the rock slab. The analyses allowed an assessment of the role of the undermining, together with the presence of an almost vertical joint set, striking sub-parallel to the cliff orientation, on the development of the slope instability processes. Based on the TLS and on the numerical simulation results, an interpretation of the landslide mechanism is proposed.

The version presented here may differ from the published version. If citing, you are advised to consult the published version for pagination, volume/issue and date of publication Mirko Francioni (a), Riccardo Salvini (b), Doug Stead (c), John Coggan (a)