Optimization of geostructural surveys in rock mass stability analyses using remote sensing techniques

Abstract

Most instability processes in carbonate rock masses, such as slides, falls and topples are related to the mobilization of discrete blocks delimited by discontinuities (i.e. bedding planes or joints) and, eventually, to the presence of caves of both natural and man-made origin. Currently, the most sophisticated methods for evaluating potential or on-going gravitational instability mechanisms are based on advanced numerical software, that are also able to consider their evolution over time. In this context, accurate geomechanical characterizations, that include quantitative descriptions of the rock masses and of on-site materials, are fundamental for an appropriate stability analysis. Field geomechanical and geostructural surveys are carried out with the aim of detecting discontinuity orientation, spacing, persistence, roughness, wall strength, aperture, filling, seepage, number of discontinuity sets, block sizes and shapes. In practice, this approach is expensive and time-consuming, with many drawbacks such as lack of significant data in areas inaccessible or with difficult logistics. The aim of this research activity is to improve the methods for the characterization of rock masses by integrating traditional field surveys with remote sensing techniques, such as Terrestrial Laser Scanning (TLS), Light Detection and Ranging (LiDAR) and, eventually, Unmanned Aerial Vehicles (UAV), in order to carry out practical and realistic discontinuous modelling. Adequate case studies will be investigated by means of traditional scanline/window mapping methods and remote sensing techniques, supported by Terrestrial Laser Scanning and, at places, high-resolution UAV (Unmanned Aerial Vehicle) data. The acquired point clouds will be processed and tested for automatic (through algorithms) and semi-automatic (through algorithms and manual control) extraction of the discontinuities and related properties, both on raw data and on meshes, with the aim of establishing the most reliable method. The comparison of the results will allow to evaluate the advantages and limits of each technique and properly combine them, in order to create accurate 3D models of the case studies. Potential instability processes and geometrically possible motion of rock blocks will be detected through kinematic analyses with the help of stereographic projections, on the basis of the geometrical relations between the slope and the discontinuities. Successively, the results will be used for numerical stability solutions, thus identifying the propensity of the case studies to gravitational processes. The choice of the most suitable software will strongly be influenced by thecalibrated geomechanical model and physical-mechanical behaviour of rock materials.