Landslides (LS) represent geomorphological processes that can induce changes over time in the physical, hydrogeological, and mechanical properties of the involved materials. For geohazard assessment, the variations of these properties might be detected by a wide range of non-intrusive techniques, which can sometimes be confusing due to their significant variation in accuracy, suitability, coverage area, logistics, timescale, cost, and integration potential; this paper reviews common geophysical methods (GM) categorized as Emitted Seismic and Ambient Noise based and proposes an integrated approach between them for improving landslide studies; this level of integration (among themselves) is an important step ahead of integrating geophysical data with remote sensing data. The aforementioned GMs help to construct a framework based on physical properties that may be linked with site characterization (e.g., a landslide and its subsurface channel geometry, recharge pathways, rock fragments, mass flow rate, etc.) and dynamics (e.g., quantification of the rheology, saturation, fracture process, toe erosion, mass flow rate, deformation marks and spatiotemporally dependent geogenic pore-water pressure feedback through a joint analysis of geophysical time series, displacement and hydrometeorological measurements from the ground, air and space). A review of the use of unmanned aerial vehicles (UAV) based photogrammetry for the investigation of landslides was also conducted to highlight the latest advancement and discuss the synergy between UAV and geophysical in four possible broader areas: (i) survey planning, (ii) LS investigation, (iii) LS dynamics and (iv) presentation of results in GIS environment. Additionally, endogenous source mechanisms lead to the appearance of deformation marks on the surface and provide ground for the integrated use of UAV and geophysical monitoring for landslide early warning systems. Further development in this area requires UAVs to adopt more multispectral and other advanced sensors where their data are integrated with the geophysical one as well as the climatic data to enable Artificial Intelligent based prediction of LS.

Back analysis is the most common method to study landslide movements after the event, and it allows us to understand how a landslide evolved along the slope. This paper presents the back-analysis of the Pomarico landslide (Basilicata, Italy) that occurred on January 25th, 2019, on the southwestern slope of the Pomarico hill. The landslide, of rotational clayey retrogressive type—planar sliding, evolved in different phases until it caused a paroxysmal movement in the early afternoon on January 29th, 2019. The landslide caused the collapse of a bulkhead (built at the end of the twentieth century) and of some buildings along the village’s main road. In this paper, a multi-layer back-analysis study is presented, based on the limit equilibrium model (LEM), applying the solution proposed by Morgenstern and Price in Geotechnique 15(1):79–93zh, (1965) and implemented in the freeware software SSAP 2010. The analysis allowed the reconstruction of the entire landslide evolution, using geotechnical parameters obtained from both laboratory and in situ tests, and data from the literature. The application of multilayer back-analysis made it possible to avoid the homogenisation of the layers, modelling the event according to the real conditions present on the slope. The use of the SSAP software made it possible to curb the problem related to the theoretical limitation of the shape of the rupture surfaces, by evaluating independently the friction angle locally and by discarding all those surfaces, which, due to this problem, presented a non-reliable factor of safety (FS) value. The modelling revealed a slope that is highly unstable as the height of the water table changes. The FS calculated under water table conditions close to ground level was less than 1 (FS = 0.98), simulating the first landslide movement (November 2018). The subsequent model reconstructed the critical surface responsible for the January 2019 movement and calculated the FS present on the slope (FS = 1.01). Eventually, the paroxysmal event on January 29th, 2019, was modelled, returning an FS of 0.83, and a sliding surface that sets below the bulkhead, causing its failure. Furthermore, the modelling of the slope in the presence of adequate retaining structures demonstrated the (non-) effectiveness of the retaining wall system represented by the bulkhead. The proposed method of analysis suggests further applications in similar complex multi-layer soil-structure interaction scenarios.

Performing a reliable stability analysis of a landslide slope requires a good understanding of the internal geometries and an accurate characterisation of the geotechnical parameters of the identified strata. Geotechnical models are commonly based on geomorphological data combined with direct and intrusive geotechnical investigations. However, the existence of numerous empirical correlations between seismic parameters (e.g., S-wave velocity) and geotechnical parameters in the literature has made it possible to investigate areas that are difficult to reach with direct instrumentation. These correlations are often overlooked even though they enable a reduction in investigation costs and time. By means of geophysical tests, it is in fact possible to estimate the N-SPT value and derive the friction angle from results obtained from environmental seismic noise measurements. Despite the empirical character and a certain level of uncertainty derived from the estimation of geotechnical parameters, these are particularly useful in the preliminary stages of an emergency, when straight data are not available and on all those soils where other direct in situ tests are not reliable. These correlations were successfully applied to the Theilly landslide (Western Alps, Italy), where the geotechnical model was obtained by integrating the results of a multi-parameter geophysical survey (H/V seismic noise and ground-penetrating radar) with stratigraphic and geomorphological observations, digital terrain model and field survey data. The analysis of the triggering conditions of the landslide was conducted by means of hydrological–geotechnical modelling, evaluating the behaviour of the slope under different rainfall scenarios and considering (or not) the stabilisation interventions present on the slope. The results of the filtration analyses for all events showed a top-down saturation mechanism, which led to the formation of a saturated face with a maximum thickness of 5 m. Stability analyses conducted for the same events showed the development of a shallow landslide in the first few metres of saturated soil. The modelling results are compatible with the actual evolution of the phenomenon and allow us to understand the triggering mechanism, providing models to support future interventions.

One of the most used geophysical measurement techniques for soil reconstruction is the Electrical Resistivity Tomography. In many different application fields, the reconstruction of the subsurface must be accurate and precise in order to properly identify the underground target. In many practical cases this will allow to decrease the costs thanks to an easier and more accurate plan of the excavation survey. There are different array geometries that could be used in Electrical Resistivity Tomography depending on the area of investigation. Some of them uses a remote electrode (also known as remote pole) ideally located at infinite distance from the other electrodes. Obviously, since the length of the cable is finite, it is not possible to deploy the remote pole at the theoretical infinite distance. Thus, it is fundamental to understand how this error influence the subsurface reconstruction. Starting from a previous work, this paper compares the output of a Monte Carlo simulation with the results of a measurement survey carried out on an Etruscan tumulus. The location of the remote pole has been changed starting at 50 m up to 150 m from the center of the linear array. The results of both simulations and measurement campaign emphasizes the effects of a non-ideal remote pole in terms of apparent resistivity of the subsurface and colormap-based soil reconstruction.

<p>The issue of salinity in agricultural soils is a growing problem. Soil with a high sodium content in the root growth zone compromises plant health and growth. Irrigation is one of the main techniques used to reclaim high-salt soils, as water dilutes the sodium concentration. In this study, electrical resistivity tomography (ERT) is proposed as a reliable non-invasive technique to quantify sault movement during the irrigation process. The first step was to identify the best set up of electrodes for this type of investigation. 3D-ERT measurements were carried out in two different campaigns to identify the most suitable electrode distribution. The study area is a segment of land, located in Barbaruta (GR, Italy) and used for the cultivation of melons. The investigation site is characterised by irrigated soils in which an accumulation of sodium has occurred over time. To detect the movement of salt during the irrigation phases, ERT surveys were carried out before, during, and after the irrigation phases.</p><p>Considering the objective of the experiment, the measurement carried out during the first campaign (July 2021) was performed by creating a 3D grid in which the 72 electrodes were spaced 0.2 m apart and arranged in 5 parallel lines, spaced 0.2 m apart, two of which (lines 1 and 5) were 2.8 m long, for a total of 15 electrodes, and three of which (lines 2, 3 and 4) were 2.6 m long, for a total of 14 electrodes. This configuration made it possible to include two melon plants.</p><p>The survey carried out in the second campaign (August 2021) was carried out with a 3D grid in which the 72 electrodes were spaced 0.3 m apart and arranged in three parallel lines, 0.3 m apart and 6.9 m long, for a total of 24 electrodes in each line. This configuration allowed five melon plants to be incorporated. A Dipole-Dipole configuration was adopted for all the acquisition of electrical resistivity data. The commercial software ViewLab 3D was used to process the geoelectric data.</p><p>Data analysis showed that the range of conductivity values increases from dry to wet soil conditions, and conductivity increases with depth. The ERTs sections, carried out after the irrigation phase, showed areas where conductivity decreases over time during irrigation, this can be explained by the leaching of salts because of water input. While other areas show higher conductivity after irrigation, and this may mean not only an increase in water content but also a displacement of salts with water input. For this reason, further analysis is required, including the use of Induced Polarisation (IP).</p><p>The test showed that the best configuration is the one with the electrodes arranged in three lines, as it allows more plants to be incorporated.</p><p>The test also led to the need to avoid stressing the plants during the measurement phase. This made it necessary to create a special set of electrodes to be installed during the transplanting phase, so as not to disturb the plants during the growth phas.</p>