Use of Digital Terrestrial Photogrammetry in rocky slope stability analysis by Distinct Elements Numerical Methods

Current approaches to rocky slope stability analysis require knowledge of the geometrical-structural setting, as well as the physical-mechanical properties of the intact material and its discontinuities. The physical-mechanical properties are derived from in situ and laboratory tests, while the geometrical characteristics come from field attitude measurements. Frequently, the inaccessibility of walls does not allow direct measurement of discontinuity surfaces by traditional geological methods. In such cases, data can only be obtained by statistical methods. Although this approach is significant and provides spatial meaning, it is ineffective for deterministic analysis. This paper provides a solution to this problem by applying digital terrestrial photogrammetric techniques employing a reamed bar, an aerostatic balloon and a helicopter. Results demonstrate that the accuracy and the quantity of geometrical and engineering-geological data coming from the photogrammetric survey, allow for numerical simulation of the relationship between rock elements as a function of their physical-mechanical properties and load conditions. The 3DEC code was chosen among the different methods available to model the discontinuous media through distinct elements. The proposed methodology was applied to a quarry located in the Carrara Marble District (the Apuan Alps, Italy), the largest and most exploited mining region in Europe. The economic value of the area required a detailed study of the presence of instability phenomena so that marble extraction could continue in safe conditions.