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To clarify the mechanism of deep-seated gravitational slope deformation (DSGSD), we investigated crushed rocks and subsurface deformation in a slope southwest of Akatani landslide, in Gojo city, Japan, on which a deep-seated catastrophic rapid landslide occurred in 2011. We analyzed subsurface deformation from 2017 to 2022 using monthly inclinometer data from three 85–90 m deep cored boreholes. Crushed rocks were investigated based on visual observations of the core. We examined the fractures of rock in the borehole wall based on borehole camera images. The inclinometer measurements within the DSGSD slope indicated that sliding occurred in the upper slope, and sagging occurred in the mid-slope, with two sliding surfaces identified at depths of 47.5 and 54.5 m. At a depth of 47.5 m, the average annual displacement increased by one order of magnitude when the groundwater level rose remarkably due to rainfall. This suggests that the movement of slope transitioned from sagging to sliding under the action of rising groundwater in the mid-slope. There was more crushed rock in the cores from the upper slope, where sliding occurs, than in the cores from the mid-slope, where sagging occurs. The fractures of rock by the number and width of the cracks were also greater in the upper slope cores than in the mid-slope cores. Our results support that the sliding progressed from the head to the toe of the slope. [ABSTRACT FROM AUTHOR]

This paper presents the first attempt at establishing the dynamics of the Šumljak debris slide by using a multidisciplinary approach, including long-term inclinometer and piezometer measurements and a time-series analysis of SAR images for displacement vector estimation. The Šumljak landslide is located in the Rebrnice area, SW Slovenia, where the regional highway Razdrto-Nova Gorica runs through and poses a threat to the highway viaduct’s stability. By combining both ascending and descending Sentinel-1 data, we have estimated 3D displacement vectors for the landslide, providing insights into the usability of the technique for this kind of slow-moving landslides. Furthermore, we have combined and compared the SBAS DInSAR results to the displacements measured by inclinometer to evaluate the rate of displacement of the landslide and the viaduct. The inclinometer measurement results show that the landslide has a single sliding plane between the flysch colluvium and the slope deposits and provide the proof of the enlargement of the sliding area above its main scarp. The displacement vectors are spatially heterogenous, suggesting that different sites have different velocities and slightly different directional vectors. These results partly comply with the InSAR results. We further discussed the estimated vectors of displacement and the possible mechanism of movements. By using the piezometric data, we studied the groundwater level fluctuation in relation to daily rainfall and its influence on the displacements. Our findings show a correlation between the movements and the wet/dry season, indicating that the landslide is driven by rainfall and consequently groundwater level fluctuation. In 2020, the groundwater level rise was smaller than in the years before due to less rainfall, resulting in lower velocity of the landslide (5.5 mm/year) than in 2019 (7 mm/year). [ABSTRACT FROM AUTHOR]

This study presents the employment of automatic deep drainage systems to stabilize the Mendatica landslide, one of the largest relict landslides of western Liguria (north-western Italy). Despite the relict state of activity of the main landslide body, a residual kinematic still affects the sector of accumulation zone over which the small village of Mendatica is located and where sharp reactivations of the movements were frequently recorded after severe rainstorms. The aim of this research is to investigate both the efficiency and effectiveness of Electropneumatic Drains® during an extreme rainstorm based on geotechnical monitoring data. On the one hand, the continuous groundwater level measurements allowed to examine the performance of two alignments of wells equipped with electropneumatic pumps during a severe 5-day rainfall event occurred in November 2016, when cumulative rainfalls equalled approximately 800 mm at Mendatica. On the other hand, the subsurface displacements measured from inclinometers before and after the activation of the two draining diaphragms enabled the evaluation of the influence of the automatic deep drainage on the landslide kinematic. The analysis of the hydraulic response of the two drainage lines reveals that, despite the severity of the recorded rainfall values, the pumping wells efficiently worked during the rainstorm since they successfully controlled the increase of hydraulic heads. Furthermore, the outcomes of this study show that, under severe rain conditions, the presence of the Electropneumatic Drains® has mitigated the magnitude of the landslide displacements preventing the development of rapid accelerations of the slope movements. [ABSTRACT FROM AUTHOR]

The displacement of a large slow-moving landslide is accompanied by slope damage, such as fractures, tension cracks, and slope bulging. Studies of these features provide insight into the mechanisms responsible for the deformation. In this paper, we investigate slope damage at the Downie Slide, a very large landslide in British Columbia, Canada, that is slowly moving along two shear zones subparallel to the ground surface. Structural geology, and particularly the morphology of the lower shear zone, strongly controls the deformation and, in turn, the observed internal and surficial slope damage features. We use aerial and underground adit laser scanning and photogrammetry to characterize the geometry of the landslide. We subdivide the slide area into slope damage domains based on the distribution, size, and orientation of the slope damage features. We reconstruct the shape of the two failure surfaces by interpolating borehole inclinometer monitoring data and processing the 3D surfaces in a GIS environment to create aspect and slope maps. We observe a strong correlation between surficial slope damage features and changes in the dip and dip direction of the lower sliding surface. We further infer the presence of a multi-planar failure surface geometry and previously unrecognized structurally controlled damage zones. [ABSTRACT FROM AUTHOR]

The reconnaissance, mapping and analysis of kinematic features of slow-moving landslides evolving along medium-deep sliding surfaces in urban areas can be a difficult task due to the presence and interactions of/with anthropic structures/infrastructures and human activities that can conceal morphological signs of landslide activity. The paper presents an integrated approach to investigate the boundaries, type of movement, kinematics and interactions (in terms of damage severity distribution) with the built environment of a roto-translational slow-moving landslide affecting the historic centre of Lungro town (Calabria region, southern Italy). For this purpose, ancillary multi-source data (e.g. geological-geomorphological features and geotechnical properties of geomaterials), both conventional inclinometer monitoring and innovative non-invasive remote sensing (i.e. A-DInSAR) displacement data were jointly analyzed and interpreted to derive the A-DInSAR-geotechnical velocity (DGV) map of the landslide. This result was then cross-compared with detailed information available on the visible effects (i.e. crack pattern and width) on the exposed buildings along with possible conditioning factors to displacement evolution (i.e. remedial works, sub-services, etc.). The full integration of multi-source data available at the slope scale, by maximizing each contribution, provided a comprehensive outline of kinematic-geometric landslide features that were used to investigate the damage distribution and to detect, if any, anomalous locations of damage severity and relative possible causes. This knowledge can be used to manage landslide risk in the short term and, in particular, is propaedeutic to set up an advanced coupled geotechnical-structural model to simulate both the landslide displacements and the behavior of interacting buildings and, therefore, to implement appropriate risk mitigation strategies over medium/long period. [ABSTRACT FROM AUTHOR]

New radar satellites provide global coverage and the possibility of long-term, regular frequency (days-weeks) surface displacement measurements through the application of high precision multi-temporal InSAR (Synthetic Aperture Radar Interferometry) techniques. This represents an excellent opportunity to investigate and improve our understanding of the behavior of extremely slow landslides, as well as of the long- to short-term controls of their activity. In urban settings, such landslides deserve special attention, as their cumulative movements can cause significant socio-economic damage. Here, we re-examine the case of a long-lived, deep-seated landslide in the Apennine Mountains (Italy) which was urbanized between the late 1970s and early 2000s. The case provides a rare opportunity to highlight the benefits of the integrated analysis of long-term (several years) borehole inclinometer measurements with 15 years of multi-temporal InSAR displacement data. We present evidence of the landslide composite nature and asymmetry, and draw attention to the recent period of accelerated movement that coincided with the foot failure event. This helps constraining the interpretation of the borehole and InSAR data and demonstrating the predominantly rotational landslide mechanism. We show how a detailed analysis of sparse inclinometer and more spatially continuous InSAR measurements, when combined with local rainfall records, can reveal long- to short-term patterns of temporal variability in landslide motions and allow anticipating the consequences of future landslide activity. [ABSTRACT FROM AUTHOR]

This paper assesses potential slope movement in a landslide area using a grouted cable of time domain reflectometry (TDR) technology compared with data from an inclinometer and bore logs. The paper quantifies the magnitude of a TDR coaxial cable by laboratory shear and extension tests. The maximum and average magnitudes of cable deformation by laboratory shear failure were 60 mm and 47 mm, respectively. Then, in the paper, the results of the laboratory testing were applied to a case study where there were two inclinometers and two TDR monitoring stations. Based on laboratory shear and extension testing, differences in TDR-reflected waveforms can be regarded as locations of cable deformations. Meanwhile, the magnitude of cable deformations can be measured by the regression equation of the relation between reflection coefficients and shear displacements. Finally, the working limit of the cable for potential slope movement can be determined at 210-mρ reflection coefficient in laboratory and field testing. When a grouted cable ruptured, the TDR technology can detect a reflection coefficient at 210 mρ corresponding to the potential shear displacement at approximately 47 mm, which means that a localized slope deformation significantly occurred at the location of the cable rupture. [ABSTRACT FROM AUTHOR]

A full-scale landslide-triggering experiment was conducted on a natural sandy slope subjected to an artificial rainfall event, which resulted in mobilisation of 130 m3 of soil mass. Novel slope deformation sensors (SDSs) were applied to monitor the subsurface pre-failure movements and the precursors of the artificially triggered landslide. These fully automated sensors are more flexible than the conventional inclinometers by several orders of magnitude and therefore are able to detect fine movements (< 1 mm) of the soil mass reliably. Data from high-frequency measurements of the external bending work, indicating the transmitted energy from the surrounding soil to these sensors, pore water pressure at various depths, horizontal soil pressure and advanced surface monitoring techniques, contributed to an integrated analysis of the processes that led to triggering of the landslide. Precursors of movements were detected before the failure using the horizontal earth pressure measurements, as well as surface and subsurface movement records. The measurements showed accelerating increases of the horizontal earth pressure in the compression zone of the unstable area and external bending work applied to the slope deformation sensors. These data are compared to the pore water pressure and volumetric water content changes leading to failure. [ABSTRACT FROM AUTHOR]

Mass movements of different thicknesses and types affect the slope where the Greci and Piscopie villages lie (Lago, Calabria, Italy). The study concerns a moderately urbanized area where the lithological, structural, and hydrogeological conditions have produced a large and complex unstable area. In the study area, a multi-temporal field survey has allowed for detailed landslide inventory mapping and definition of the geometric and kinematic characteristics of mass movements with long-term monitoring. In particular, an integrated monitoring network was progressively put in place, since 1996 to measure superficial and deep displacements (GPS stations and inclinometers). The network dataset shows that the mass movements in the study area are characterized by an extremely slow or very slow rate of displacement. The elements acquired by a long-term monitoring of the deep displacements point out that the landslide bodies are prone to develop new failure surfaces progressively shallower, with a consequent increase of the hazard. Moreover, medium-deep and deep-seated landslides may rapidly accelerate in relation to rainfall conditions and significantly affect structures and infrastructures. The integration of the geological and geomorphological knowledges with the monitoring data allows for distinguishing six different homogeneous sectors on the slope, as well as the relative geometric and kinematic characteristics, and the type of mass movements. In the study area, which is representative of several aspects of other areas, the method proposed and the knowledge acquired by long-term monitoring could be useful to define mass movement mechanisms, geotechnical models, and risk mitigation strategies. [ABSTRACT FROM AUTHOR]

This article presents a multidisciplinary approach to the assessment of slope deformation at the Lower Hodruša mining water reservoir, which is part of a UNESCO cultural heritage site. The multidisciplinary approach was used to develop remedial measures. The Lower Hodruša mining water reservoir is situated in the Hodruša-Hámre municipality near Banská Štiavnica in the central part of Slovakia. The first mention of the construction of the reservoir is from 1743, and according to historical records, there were problems with slope stability already at that time. Nowadays, to increase the volume of water available for technical operations in the Hodruša valley, the decision was made to increase the dam’s output capacity. Slope movements were first detected while the reservoir was being drained. A part of the left shore 50 to 150 m from the dam crest moved, damaging adjacent buildings. The Hodruša-Hámre municipal authorities declared an emergency on 24 August 2015 because of the appearance of cracks in the asphalt surface of the national road and its subsidence. The main discontinuity conformed approximately to the contours of the known landslide area on the south side of the reservoir. The significant deformations involving the 0.20-m subsidence of the service road were reported during heavy rainfall in October 2014. A range of geoscientific disciplines was used to develop a detailed description of the landslide area and to determine the cause of the slope deformation. The depth and course of the shear surface were measured using boreholes and geophysical methods; the historic development of the landslide was analysed using dendrochronological measurements; and the present horizontal and vertical movement of the landslide over one and half years was determined using geodetic monitoring based on a network of stabilised points and inclinometer measurements. [ABSTRACT FROM AUTHOR]

This paper focuses on the potential influence of rainfall parameters and reservoir levels on displacement of a reservoir landslide. Displacements were monitored by a borehole inclinometer and four surface survey points. Monitoring data were obtained from 1985 to 2010, covering the periods before, during, and after impoundment of the reservoir. A simple stability analysis has been performed to understand the real influence of reservoir level changes on slope stability and to interpret the movement pattern during the impoundment period. Analyses of available data indicate that the overall trend of the displacement could be characterized by three distinct periods, corresponding to a slow creep phase before infilling, a sharp increase in velocity during the infilling, and another slow creep phase after infilling. Displacement rates show slight fluctuation in both 'slow creep' episodes. Before impoundment, the displacement pattern was clearly controlled by rainfall, in which the displacement rate during the rainy period was twice that in the dry period. Displacement response to rainfall had a time lag of about 1-2 months. During the first 75 days of impoundment, displacement increased quickly with a linear trend, following the rising of the reservoir level with a rate of 2 m/day. Then, the displacement rate gradually decreased after the infilling of the reservoir until velocities slightly higher than that were measured before the infill. The result of the stability analysis coincides with this trend, indicating the complex effect of the impoundment: First, the decrease of stability of the landslide prevails over the increase in lateral support of the reservoir lake, while at a critical level, the increase in lateral support prevails over the decrease in stability. During the period of normal operations, an inverse relation between water level fluctuations and velocity fluctuations was observed, and rainfall had no significant effect on the sliding motion, with the exception that surface displacements showed a slight increase. [ABSTRACT FROM AUTHOR]

This paper analyzes the effects of a historical rain series on pore water pressure distribution in the Costa della Gaveta landslide, in the Southern Apennine, Italy. The effects of pore water pressure variations on the safety factor and on the displacement rate of the landslide are also analysed. The aim of the investigation is to reach a deeper understanding of the influence of hydrological parameters on the mechanism of movements of the widespread type of active, very slow landslides in fine-grained soils. Pore water pressures were evaluated by means of the 3D finite difference code MODFLOW, applying as boundary condition the long historical rainfall series of the site. The transient analysis carried out with a daily resolution successfully reproduces the trend of piezometric data. The results show that because of the subsoil low permeability ( k = 10-10 m/s), pore water pressure variations caused by rain are significant only at depths lower than about 10 m. Furthermore, noticeable depth-depending time lag is evaluated between the external hydrological input and responses of internal pore water pressures. Pore water pressure variations on the shallowest areas of the slip surface have the greatest influence on the 3D limit equilibrium safety factor and thus on the landslide movements. As a matter of fact, the safety factor seems to be well correlated to the displacement rates evaluated by inclinometers at various depths, on the slip surface. The results of the 3D model provide pore water pressure distributions which are significantly different, both in value and in time trend, from those obtained by using 2D models. [ABSTRACT FROM AUTHOR]

Slope failures world-wide cause many thousands of deaths each year and damage built environment infrastructure, costing billions of pounds to repair, resulting in thousands of people being made homeless and the breakdown of basic services such as water supply and transport. There is a clear need for affordable instrumentation that can provide an early warning of slope instability to enable the evacuation of vulnerable people and timely repair and maintenance of critical infrastructure. An approach, Assessment of Landslides using Acoustic Real-time Monitoring Systems (ALARMS) is described in the paper, and results of a field trial of sensors on an active landslide at Hollin Hill, North Yorkshire, UK, are described. Continuous and real-time monitoring of acoustic emission generated by the deforming slope has been compared to traditional inclinometer slope displacement measurements. Analysis of the results has established that there is a direct relationship between acoustic emission rate and displacement rate trends triggered by rainfall events. The technique has provided insight into reactivated slope movement kinematics. [ABSTRACT FROM AUTHOR]

The Ancona landslide is a complex, deep-seated landslide displaying composite rotational-translational kinematisms and affecting a large urban area in the Ancona municipality on the Adriatic coast of central Italy. The landslide was reactivated with a large and destructive event on 13 December 1982 following a long period of precipitation and has remained active since. This paper focuses on the estimation of the landslide kinematics (more specifically, the horizontal and vertical components of average yearly velocity) for subsequent estimation of risk for a set of 39 buildings as presented in a companion paper. The study relies both on the processing of inclinometer and radar interferometer monitoring data through statistical procedures. Triggering factors are not investigated. Outputs from the two sets of monitoring data are compared quantitatively and qualitatively. The inherent limitations in available data are discussed. The validity of the quantitative results in the context of the risk estimation effort is discussed. [ABSTRACT FROM AUTHOR]

This paper illustrates the quantitative estimation of specific risk (i.e., the product of hazard and vulnerability) for 39 buildings located upon the Ancona landslide based on the characterization of landslide kinematics presented in a companion paper. Hazard is quantified based on intensity, intended as the damaging potential of the kinetic and/or geometric attributes of the landslide, and is expressed in terms of expected exceedance of preset cumulative displacement thresholds for a set of five reference time intervals, ranging from 1 to 100 years. The estimation of hazard relies sequentially on (1) Monte Carlo simulation of displacement series, with sampling distributions of average yearly displacement defined on the basis of the statistical processing of inclinometer and radar interferometer data; and (2) the subsequent spatialization of displacement using radial basis interpolation as described in the companion paper. The vulnerability of the set of buildings relies on a quantitative model in which vulnerability is a function of landslide intensity and the resilience of the buildings. Resilience is a function of a set of indicators including structural type, age, and foundation type and is temporally variable due to the progressive structural degradation. Hazard, vulnerability, and specific risk are estimated for the set of five aforementioned reference time intervals. The magnitude and temporal dependence of hazard, vulnerability, and specific risk are assessed critically. [ABSTRACT FROM AUTHOR]

A ground model of an active and complex landslide system in instability prone Lias mudrocks of North Yorkshire, UK is developed through an integrated approach, utilising geophysical, geotechnical and remote sensing investigative methods. Surface geomorphology is mapped and interpreted using immersive 3D visualisation software to interpret airborne light detection and ranging data and aerial photographs. Subsurface structure is determined by core logging and 3D electrical resistivity tomography (ERT), which is deployed at two scales of resolution to provide a means of volumetrically characterising the subsurface expression of both site scale (tens of metres) geological structure, and finer (metre to sub-metre) scale earth-flow related structures. Petrophysical analysis of the borehole core samples is used to develop relationships between the electrical and physical formation properties, to aid calibration and interpretation of 3D ERT images. Results of the landslide investigation reveal that an integrated approach centred on volumetric geophysical imaging successfully achieves a detailed understanding of structure and lithology of a complex landslide system, which cannot be achieved through the use of remotely sensed data or discrete intrusive sampling alone. [ABSTRACT FROM AUTHOR]

The present paper illustrates the results of an integrated study of a large landslide located on the southern slope of Mount la Civita (Molise, Southern Apennine), an E-W elongated, SSE dipping and 890-m-high monocline carbonate ridge. The upper part of the slope affected by the landslide is largely controlled by strata attitude while its basal part is marked by a strike-slip fault causing the tectonic juxtaposition of the carbonate successions against predominantly clayey flysch units. An integrated study, including geological, geomorphological and geotechnical investigations, was carried out to determine the features of the landslide and to plan further investigation and monitoring. In particular, from 2002 to 2004, Differential Global Positioning System monitoring and core drillings, coupled with inclinometer measurements, were carried out to determine the landslide's kinematics, extent, depth to the surface of rupture and rates of movement. Inclinometer data revealed the presence of the rupture surface at a depth of about 20 m. DGPS monitoring allowed rates of movement up to several tens of centimetres per year to be recorded. The nearby village of Civitanova del Sannio can still be considered at risk due to the landslide, as recent remedial works, consisting mainly of very shallow re-shaping of the slope by blasting and partial filling of trenches, did not succeed in stopping its movement. [ABSTRACT FROM AUTHOR]

Past landslides have been recognized in the Battice area in E-Belgium. In contrast to the other inactive landslides, the Manaihan landslide responded immediately to heavy rainfall events in the last two decades. This study aims to map its spatial extent and the dominant surface features; to measure surface displacement using GPS; to investigate subsurface structure with Cone penetration test (CPT) and corings; and to determine the depth of the shear surface by inclinometers. Results show a partial landslide reactivation. Surface velocities range between 20 and 40 cm/year and are strongly dependent on winter rainfall. CPT results give clear boundaries between the landslide mass and the undisturbed bedrock in the head scarp. Distinct shear surfaces have been determined with displacement rates up to 15.8 mm in 21 days. Further research should apply geophysical methods for two-dimensional information on the ground, investigate geotechnical properties of the landslide mass, model slope instability, and determine the influence of a sewage pipe crossing the central landslide mass as a potential cause for landslide activity. [ABSTRACT FROM AUTHOR]