The combined use of Uncrewed Aerial Vehicles (UAVs) with an integrated Real Time Kinematic (RTK) Global Navigation Satellite System (GNSS) module and an external GNSS base station allows ...photogrammetric surveys with centimeter accuracy to be obtained without the use of ground control points. This greatly reduces acquisition and processing time, making it possible to perform rapid monitoring of landslides by installing permanent and clearly recognizable optical targets on the ground. In this contribution, we show the results obtained in the Ca’ Lita landslide (Northern Apennines, Italy) by performing multi-temporal RTK-aided UAV surveys. The landslide is a large-scale roto-translational rockslide evolving downslope into an earthslide–earthflow. The test area extends 60 × 103 m2 in the upper track zone, which has recently experienced two major reactivations in May 2022 and March 2023. A catastrophic event took place in May 2023, but it goes beyond the purpose of the present study. A total of eight UAV surveys were carried out from October 2020 to March 2023. A total of eight targets were installed transversally to the movement direction. The results, in the active portion of the landslide, show that between October 2020 and March 2023, the planimetric displacement of targets ranged from 0.09 m (in the lateral zone) to 71.61 m (in the central zone). The vertical displacement values ranged from −2.05 to 5.94 m, respectively. The estimated positioning errors are 0.01 (planimetric) and 0.03 m (vertical). The validation, performed by using data from a permanent GNSS receiver, shows maximum differences of 0.18 m (planimetric) and 0.21 m (vertical). These results, together with the rapidity of image acquisition and data processing, highlight the advantages of using this rapid method to follow the evolution of relatively rapid landslides such as the Ca’ Lita landslide.
Flow‐like landslides in clay slopes pose major threats to people and infrastructure, which has led to numerous studies in recent decades. However, the mechanisms leading to the solid–fluid transition ...in clay are still poorly understood, despite numerous studies on its rheological evolution. The aim of this study is to contribute to quantify the degradation of clay at the surface of the Harmalière landslide (French Alps) from the analysis of a series of three unmanned aerial vehicle (UAV) acquisitions. Two approaches were combined to process the acquired optical images. First, image classification was performed applying object‐based image analysis (OBIA) to the red, green and blue (RGB) and surface roughness layers. Second, deeper analysis of the surface roughness allows to describe the morphology evolution and to interpret the degradation scheme from undegraded clay to degraded clay.
The study shows that the applied methodology is appropriate to perform a thorough analysis of the material degradation pattern on the surface of a landslide. The temporal analysis shows an average degradation rate leading to the complete degradation of a block in about 2 years. Meanwhile, a spatial analysis shows that non‐degraded clays degrade faster in the lower part of the study area, reactivated 30 years ago, than in the upper part, reactivated only a few years ago. In addition, roughness analyses enabled to highlight the evolution of the morphology during the degradation process of the clay blocks, from angular blocks to mounds.
The study uses unmanned aerial vehicle (UAV) photogrammetry to perform an in‐depth analysis of the degradation pattern leading to the solid–fluid transition in a clay landslide. The method consists of two steps. First, a classification of the surface materials was used to calculate an average degradation rate and analyse it in time and space. Second, a roughness analysis was used to highlight the evolution of the morphology during the degradation process of the clay blocks, from angular blocks to mounds.
ABSTRACT
In the past decade, passive seismic methods have shown the possibility to detect significant changes in surface wave velocity up to several days prior to landslide failure, even with sensors ...located outside the unstable zone. Electrical resistivity tomography has also long been used to monitor hydrological changes in landslides. However, the displacement of electrodes relative to each other during landslide movement induces a modification of the geometric factors and, hence, of the apparent resistivity. The first objective of this work is to evaluate the possibility of monitoring the Pont‐Bourquin landslide (Swiss Alps) with electrodes located outside the unstable zone. The second objective is to monitor both seismic velocity and electrical resistivity to get insights into the evolution with time of mechanical and hydrological parameters, respectively. The sliding mass was first imaged in three dimensions to produce a resistivity starting model for the further inversion of time‐lapse data. Daily time series (235 days from February to November 2015) showed that changes are detected but cannot be spatially localized, in agreement with numerical simulation results. At the seasonal scale, resistivity and seismic time series are positively correlated with temperature and suggest a control by superficial water content. On the scale of a few days, geophysical parameters are negatively correlated with precipitation and suggest rapid infiltration of water into the ground. Although laboratory experiments show that no change in resistivity occurs during fluidization, and since no flow occurred during the monitoring period the evolution of resistivity during a flow event remains an open question.
The assessment of hazards associated with active landslides and the related risk management takes advantage nowadays of using the integration of information arising from field monitoring data, ...including both displacement data, at ground surface and at depth, and pore pressure measurements well distributed throughout the landslide area, along with the results of numerical models. This paper provides an example of the application of this methodological approach to a case study represented by an active sector of the large Montaguto earthslide, located in the Italian Southern Apennines, which has shown in recent years a continuous slow movement, despite the draining interventions executed in 2011 and the general stability of the other portions of the earthslide. The near real-time topographic monitoring network installed in 2010 shows the presence of different kinematic sectors within the same landslide body, characterised by different velocities and evolution trends. After the proper emergency phase occurred in 2010, a specific area has still shown in 2011 and 2012 clear signs of activity, with acceleration stages generally recorded in the Spring. In order to explore the factors that presumably control the activity of this landslide sector, a two-dimensional finite element model has been developed by using PLAXIS-2D code. Based on the available geological information, pore water pressure measurements and soil geotechnical properties, the numerical results indicate the role of geometry of the landslide mass in sector E as a factor promoting the instability of this specific area. The numerical results are in good agreement with the displacement field measured throughout the landslide channel and confirm that numerical modelling can represent a reliable support for the interpretation of the landslide failure mechanism and the corresponding evolution, when calibrated against the in situ landslide behaviour reconstructed through a monitoring system.
