An Integrated Procedure to Assess the Stability of Coastal Rocky Cliffs: From UAV Close-Range Photogrammetry to Geomechanical Finite Element Modeling

The present paper explores the combination of unmanned aerial vehicle (UAV) photogrammetry and three-dimensional geomechanical modeling in the investigation of instability processes of long sectors of coastal rocky cliffs. The need of a reliable and detailed reconstruction of the geometry of the cliff surfaces, beside the geomechanical characterization of the rock materials, could represent a very challenging requirement for sub-vertical coastal cliffs overlooking the sea. Very often, no information could be acquired by alternative surveying methodologies, due to the absence of vantage points, and the fieldwork could pose a risk for personnel. The case study is represented by a 600 m long sea cliff located at Sant’Andrea (Melendugno, Apulia, Italy). The cliff is characterized by a very complex geometrical setting, with a suggestive alternation of 10 to 20 m high vertical walls, with frequent caves, arches and rock-stacks. Initially, the rocky cliff surface was reconstructed at very fine spatial resolution from the combination of nadir and oblique images acquired by unmanned aerial vehicles. Successively, a limited area has been selected for further investigation. In particular, data refinement/decimation procedure has been assessed to find a convenient three-dimensional model to be used in the finite element geomechanical modeling without loss of information on the surface complexity. Finally, to test integrated procedure, the potential modes of failure of such sector of the investigated cliff were achieved. Results indicate that the most likely failure mechanism along the sea cliff examined is represented by the possible propagation of shear fractures or tensile failures along concave cliff portions or over-hanging due to previous collapses or erosion of the underlying rock volumes. The proposed approach to the investigation of coastal cliff stability has proven to be a possible and flexible tool in the rapid and highly-automated investigation of hazards to slope failure in coastal areas.

[1]  M. Dubbini,et al.  Combining nadir and oblique UAV imagery to reconstruct quarry topography: methodology and feasibility analysis , 2017 .

[2]  Carlos Castillo,et al.  Image-based surface reconstruction in geomorphometry - merits, limits and developments , 2016 .

[3]  Roberto Tomás,et al.  Characterization of rock slopes through slope mass rating using 3D point clouds , 2016 .

[4]  N. Rosser,et al.  Identifying the behavioural characteristics of clay cliffs using intensive monitoring and geotechnical numerical modelling , 2010 .

[5]  E. Dimas,et al.  3D geometric modelling based on NURBS: a review , 1999 .

[6]  Heiko Hirschmüller,et al.  Stereo Processing by Semiglobal Matching and Mutual Information , 2008, IEEE Trans. Pattern Anal. Mach. Intell..

[7]  S. Robson,et al.  Straightforward reconstruction of 3D surfaces and topography with a camera: Accuracy and geoscience application , 2012 .

[8]  Riccardo Roncella,et al.  Rock slopes risk assessment based on advanced geostructural survey techniques , 2011 .

[9]  Larry L. Schumaker,et al.  Triangulations in CAGD , 1993, IEEE Computer Graphics and Applications.

[10]  P. Lollino,et al.  Role of Brittle Behaviour of Soft Calcarenites Under Low Confinement: Laboratory Observations and Numerical Investigation , 2017, Rock Mechanics and Rock Engineering.

[11]  M. Parise,et al.  A three-dimensional back-analysis of the collapse of an underground cavity in soft rocks , 2017 .

[12]  Giovanni Grasselli,et al.  A review of discrete modeling techniques for fracturing processes in discontinuous rock masses , 2014 .

[13]  A. Corsini,et al.  Integrating airborne and multi‐temporal long‐range terrestrial laser scanning with total station measurements for mapping and monitoring a compound slow moving rock slide , 2013 .

[14]  Jose Antonio Fernandez Merodo,et al.  Evaluation of the Stability of Underground Cavities in Calcarenite Interacting with Buildings Using Numerical Analysis , 2015 .

[15]  M. Johnson-Roberson,et al.  Kite Aerial Photography for Low-Cost, Ultra-high Spatial Resolution Multi-Spectral Mapping of Intertidal Landscapes , 2013, PloS one.

[16]  Patrick J. Flynn,et al.  A Survey Of Free-Form Object Representation and Recognition Techniques , 2001, Comput. Vis. Image Underst..

[17]  M. Westoby,et al.  ‘Structure-from-Motion’ photogrammetry: A low-cost, effective tool for geoscience applications , 2012 .

[18]  Vincent G. Ambrosia,et al.  Unmanned Aircraft Systems in Remote Sensing and Scientific Research: Classification and Considerations of Use , 2012, Remote. Sens..

[19]  Doug Stead,et al.  Advanced numerical techniques in rock slope stability analysis - applications and limitations , 2001 .

[20]  P. Mazzanti,et al.  Integrating geomechanical surveys and remote sensing for sea cliff slope stability analysis: the Mt. Pucci case study (Italy) , 2014 .

[21]  Steven M. Seitz,et al.  Photo tourism: exploring photo collections in 3D , 2006, ACM Trans. Graph..

[22]  C. Prisco,et al.  Experimental Study on the Water-Induced Weakening of Calcarenites , 2015, Rock Mechanics and Rock Engineering.

[23]  F. Agüera-Vega,et al.  Accuracy of Digital Surface Models and Orthophotos Derived from Unmanned Aerial Vehicle Photogrammetry , 2017 .

[24]  John Coggan,et al.  Landslides: Numerical modeling of rock-slope instability , 2012 .

[25]  Mark A. Fonstad,et al.  Topographic structure from motion: a new development in photogrammetric measurement , 2013 .

[26]  C. Delacourt,et al.  Landslide detection and monitoring capability of boat-based mobile laser scanning along Dieppe coastal cliffs, Normandy , 2015, Landslides.

[27]  Samuel T. Thiele,et al.  Ground-based and UAV-Based photogrammetry: A multi-scale, high-resolution mapping tool for structural geology and paleoseismology , 2014 .

[28]  D. Varnes,et al.  Landslide types and processes , 2004 .

[29]  F. Nex,et al.  UAV for 3D mapping applications: a review , 2014 .

[30]  J. Leroux,et al.  CLIFF COLLAPSE HAZARD FROM REPEATED MULTICOPTER UAV ACQUISITIONS: RETURN ON EXPERIENCE , 2016 .

[31]  Greg Turk,et al.  Fast and memory efficient polygonal simplification , 1998 .

[32]  Piernicola Lollino,et al.  A preliminary analysis of failure mechanisms in karst and man-made underground caves in Southern Italy , 2011 .

[33]  Eija Honkavaara,et al.  Point Cloud Generation from Aerial Image Data Acquired by a Quadrocopter Type Micro Unmanned Aerial Vehicle and a Digital Still Camera , 2012, Sensors.

[34]  A. B. Hawkins,et al.  Limestone weathering: its engineering significance and a proposed classification scheme , 1988, Quarterly Journal of Engineering Geology.

[35]  David M. Cruden,et al.  LANDSLIDES: INVESTIGATION AND MITIGATION. CHAPTER 3 - LANDSLIDE TYPES AND PROCESSES , 1996 .

[36]  Nicola Walsh,et al.  The effects of wetting and drying, and marine salt crystallization on calcarenite rocks used as building material in historic monuments , 2007, Geological Society, London, Special Publications.

[37]  G. Andriani,et al.  Petrophysical and mechanical properties of soft and porous building rocks used in Apulian monuments (south Italy) , 2010 .

[38]  Arko Lucieer,et al.  The Impact of the Calibration Method on the Accuracy of Point Clouds Derived Using Unmanned Aerial Vehicle Multi-View Stereopsis , 2015, Remote. Sens..

[39]  Tamotsu Matsui,et al.  Finite element slope stability analysis by shear strength reduction technique , 1992 .

[40]  Marco Dubbini,et al.  Using Unmanned Aerial Vehicles (UAV) for High-Resolution Reconstruction of Topography: The Structure from Motion Approach on Coastal Environments , 2013, Remote. Sens..

[41]  M. Piras,et al.  Detailed geological mapping in mountain areas using an unmanned aerial vehicle: application to the Rodoretto Valley, NW Italian Alps , 2017 .

[42]  Andrea Manconi,et al.  Brief Communication: The use of an unmanned aerial vehicle in a rockfall emergency scenario , 2015 .

[43]  Michel Jaboyedoff,et al.  "Use of 3D Point Clouds in Geohazards" Special Issue: Current Challenges and Future Trends , 2016, Remote. Sens..

[44]  K. Oost,et al.  Reproducibility of UAV-based earth topography reconstructions based on Structure-from-Motion algorithms , 2016 .

[45]  F. Nex,et al.  OBLIQUE MULTI-CAMERA SYSTEMS - ORIENTATION AND DENSE MATCHING ISSUES , 2014 .

[46]  J. Warrick,et al.  New Techniques to Measure Cliff Change from Historical Oblique Aerial Photographs and Structure-from-Motion Photogrammetry , 2016, Journal of Coastal Research.

[47]  Claudio Delrieux,et al.  Structure-from-Motion Approach for Characterization of Bioerosion Patterns Using UAV Imagery , 2015, Sensors.

[48]  Jean Ponce,et al.  Accurate, Dense, and Robust Multiview Stereopsis , 2010, IEEE Transactions on Pattern Analysis and Machine Intelligence.

[49]  P. Grussenmeyer,et al.  Surveying and modeling of rock discontinuities by terrestrial laser scanning and photogrammetry: Semi-automatic approaches for linear outcrop inspection , 2014 .

[50]  Massimo Ramondini,et al.  Use of unmanned aerial vehicles (UAVs) for photogrammetric surveys in rockfall instability studies , 2013 .

[51]  C. Bond,et al.  LiDAR, UAV or compass-clinometer? Accuracy, coverage and the effects on structural models , 2017 .

[52]  Matthijs C. Dorst.  Distinctive Image Features from Scale-Invariant Keypoints , 2011 .

[53]  Tony DeRose,et al.  Mesh optimization , 1993, SIGGRAPH.

[54]  J. Balek,et al.  A critical evaluation of the use of an inexpensive camera mounted on a recreational unmanned aerial vehicle as a tool for landslide research , 2017, Landslides.