Superficial Displacements Research Articles

Non-invasive regional parameter identification of degenerated human meniscus

Accurate identification of local changes in the biomechanical properties of the normal and degenerative meniscus is critical to better understand knee joint osteoarthritis onset and progression. Ex-vivo material characterization is typically performed on specimens obtained from different locations, compromising the tissue's structural integrity and thus altering its mechanical behavior. Therefore, the aim of this in-silico study was to establish a non-invasive method to determine the region-specific material properties of the degenerated human meniscus. In a previous experimental magnetic resonance imaging (MRI) study, the spatial displacement of the meniscus and its root attachments in mildly degenerated (n = 12) and severely degenerated (n = 12) cadaveric knee joints was determined under controlled subject-specific axial joint loading. To simulate the experimental response of the lateral and medial menisci, individual finite element models were created utilizing a transverse isotropic hyper-poroelastic constitutive material formulation. The superficial displacements were applied to the individual models to calculate the femoral reaction force in an inverse finite element analysis. During particle swarm optimization, the four most sensitive material parameters were varied to minimize the error between the femoral reaction force and the force applied in the MRI loading experiment. Individual global and regional parameter sets were identified. In addition to in-depth model verification, prediction errors were determined to quantify the reliability of the identified parameter sets. Both compressibility of the solid meniscus matrix (+141 %, p ≤ 0.04) and hydraulic permeability (+53 %, p ≤ 0.04) were significantly increased in the menisci of severely degenerated knees compared to mildly degenerated knees, irrespective of the meniscus region. By contrast, tensile and shear properties were unaffected by progressive knee joint degeneration. Overall, the optimization procedure resulted in reliable and robust parameter sets, as evidenced by mean prediction errors of <1 %. In conclusion, the proposed approach demonstrated high potential for application in clinical practice, where it might provide a non-invasive diagnostic tool for the early detection of osteoarthritic changes within the knee joint.

Image analysis and LSTM methods for forecasting surficial displacements of a landslide triggered by snowfall and rainfall

AbstractLandslide-prone areas, predominantly located in mountainous regions with abundant rainfall, present unique challenges when subject to significant snowfall at high altitudes. Understanding the role of snow accumulation and melting, alongside rainfall and other environmental variables like temperature and humidity, is crucial for assessing landslide stability. To pursue this aim, the present study focuses first on the quantification of snow accumulated on a slope through a simple parameter obtained with image processing. Then, this parameter is included in a slope displacement prediction analysis carried out with long short-term memory (LSTM) neural network. By employing image processing algorithms and filtering out noise from white-shown rocks, the methodology evaluates the percentage of snow cover in RGB images. Subsequent LSTM forecasts of landslide displacement utilize 28-day historical data on rainfall, snow, and slope movements. The presented procedure is applied to the case of a deep-seated landslide in Italy, a site that in winter 2020–2021 experienced heavy snowfall, leading to significant snow accumulation on the slope. These episodes motivated a study aimed at forecasting the superficial displacements of this landslide, considering the presence of snow both at that time and in the following days, along with humidity and temperature. This approach indirectly incorporates snow accumulation and potential melting phenomena into the model. Although the subsequent winters were characterized by reduced snowfall, including this information in the LSTM model for the period characterized by snow on the slope demonstrated a dependency of the predictions on this parameter, thus suggesting that snow is indeed a significant factor in accelerating landslide movements. In this context, detecting snow and incorporating it into the predictive model emerges as a significant aspect for considering the effects of winter snowfall. The method aims to propose an innovative strategy that can be applied in the future to the study of the landslide analyzed in this paper during upcoming winters characterized by significant snowfall, as well as to other case studies of landslides at high altitudes that lack precise snow precipitation recording instruments.

Kinematics and geomorphological changes of a destabilising rock glacier captured from close-range sensing techniques (Tsarmine rock glacier, Western Swiss Alps)

Accurately assessing landform evolution and quantifying rapid environmental changes are gaining importance in the context of monitoring techniques in alpine environments. In the European Alps, glaciers and rock glaciers are among the most characteristic cryospheric components bearing long and systematic monitoring periods. The acceleration in rock glacier velocities and the onset of destabilization processes, mainly since 1990, have raised several concerns due to the potential effects on the high alpine natural and anthropic environments. This study presents a combination of uncrewed aerial vehicle (UAV) and terrestrial laser scanning (TLS) surveys for monitoring the current changes on the quickly accelerating, destabilised Tsarmine rock glacier in the Arolla Valley, Western Swiss Alps, delivering a considerable volume of debris to a steep torrential gully. High-resolution digital elevation models (DEMs) and orthomosaics are derived from UAV image series combined with structure from motion (SfM) photogrammetry techniques. Multitemporal orthomosaics are employed for measuring spatially continuous rock glacier kinematics using image matching algorithms. Superficial displacements are evaluated with simultaneousin-situdifferential global navigation satellite system (GNSS) measurements. Elevation and volume changes are computed from TLS and UAV-derived DEMs at similar periods. Between June 2017 and September 2019, both datasets showed a similar elevation change pattern and surface thinning rates of 0.15 ± 0.04 and 0.16 ± 0.03 m yr−1, respectively. Downward of a rupture zone developing about 150 m above the front, the rock glacier doubled its overall velocity during the study period, from around 5 m yr−1between October 2016 and June 2017 to more than 10 m yr−1between June and September 2019. The kinematic information reveals striking differences in the velocity between the lower and upper rock glacier sections. The monitoring approach based on close-sensing techniques provides accurate surface velocity and volume change information, allowing an enhanced description of the current rock glacier dynamics and its surface expression.

Differential interferometry, structural lineaments and terrain deformation analysis applied in Zero Zone 2016 Earthquake (Manta, Ecuador)

The earthquake of April 16, 2016 caused huge economic losses and human lives in Ground Zero of the city of Manta, Ecuador. The present study delimited the affected areas by superficial deformation and vertical displacements of the relief in this zone by means of the differential interferometry analysis (DInSAR), with the support of geophysical techniques such as electrical tomography of the subsoil and of georadar in combination with the analysis of concentration of structural lineaments-tectonic deformation, seismicity and geotechnical parameters such as soil liquefaction indexes, cutting wave velocity Vs30, among others. This combination of techniques allowed the spatial location with greater certainty of areas susceptible to seismic risk for construction and related to the soils typology of the Ecuadorian Construction Standard-NEC 2015. This proposed methodology improved forecasting mechanisms for the reduction of seismic risk based on maps of its susceptibility to the possible occurrence of an earthquake of magnitude as that of 16 April 16, 2016. Forecast that can be done to protect engineering works and to the population, especially in tectonically deformed areas.

Full-field measurement with nanometric accuracy of 3D superficial displacements by digital profile correlation: A powerful tool for mechanics of materials

In recent decades, technological innovations have prompted the development of pioneering materials that attempt to satisfy new and forthcoming needs. The innovation in these materials is usually from their peculiar properties, which in many cases make them uniquely appropriate for a specific application. In this context, the development of innovative measurement techniques can provide more comprehensive understanding and knowledge of these materials' properties, often non-conventional and not easily retrieved by standard procedures. In order to obtain a full-field 3D displacement vector of a surface under investigation, the author proposes the combination of two well-known measurement techniques: the Confocal Microscopy (CM) and the two-dimensional Digital Image Correlation (2D-DIC). Specifically, CM has demonstrated its ability to successfully attain microscopic topography on a highly finished surface with sub-micrometric roughness, and such a technique could be used as a carrier to successfully apply the 2D-DIC algorithm. By this approach, it is not difficult to reach an accuracy of a few nanometers on the displacement measurement. The feasibility of the procedure proposed herein was demonstrated by two case studies: a tensile test of a Ni-alloy edge crack specimen, and a hardness test carried out on a thick AISI 1040 disk.

On the reactivation of a large landslide induced by rainfall in highly fissured clays

The paper discusses the field investigations, geotechnical characterization and time evolution of horizontal displacements in a wide landslide. The latter, triggered by an earthquake occurring in September 2002, is located in Sicily and involves a thick body of stiff and highly fissured clays belonging to a Varicoloured Clay formation. In order to characterise the reactivation of landslide mechanisms induced by rainfall, a three-year monitoring programme (2008–2011) was implemented to measure rain, pore water pressures, and deep and superficial displacements. The monitoring data made it possible to recognize three distinct landslides, which evolve at variable rates in different directions, within the overall landslide area. The landslides were reactivated by the increase in pore water pressures in the period autumn 2009–spring 2010. The data clearly show the mechanical role of pore water pressures in the stability of the slope and point out the dependence of the time evolution of the horizontal displacement on the pore water pressure variation induced by rainfall. Back-analysis carried out on the single landslides confirmed that they are reactivated ones since the residual shear strength is mobilised on the pre-existing sliding surfaces. The pore water pressure variation and the landslide body displacement rates can be effectively related to 5-month cumulative rainfall by simple models, characterised by three parameters. These models, calibrated on the period October 2009–September 2010, made it possible to predict the horizontal displacement rates in the ensuing time period. The displacements forecasted by the model in the period September 2010–May 2011 agree very well with the measured ones.

Stress field reconstruction in an active mudslide

Meso-scale structures from gravitational slope deformation observed in landslides and deep-seated gravitational slope failures are very similar to those of endogenous ones. Therefore we applied palaeostress analysis of fault-slip data for reconstructing the stress field of an active mudslide in Pechgraben, Austria. This complex compound landslide has developed in clayey colluvium and shale and was activated after a certain period of dormancy in June 2013. During the active motion on June 12, 2013, 73 fault-slip traces at 9 locations were measured within the landslide body. The heterogeneous fault-slip data were processed in term of palaeostresses, the reconstructed palaeostress tensor being characterized by the orientations of the three principal stress axes and the stress ratio (which provides the shape of the stress ellipsoid). The results of the palaeostress analysis were compared to airborne laser scan digital terrain models that revealed dynamics and superficial displacements of the moving mass prior and after our survey. The results were generally in good agreement with the observed landslide displacement pattern and with the anticipated stress regime according to Mohr-Coulomb failure criteria and Anderson's theory. The compressional regime was mostly registered at the toe in areas, where a compressional stress field is expected during previous mass-movement stages, or at margins loaded by subsequent landslide bodies from above. On the other hand, extension regimes were identified at the head scarps of secondary slides, subsequently on bulged ridges at the toe and in the zone of horst-and-graben structures in the lower central part of the main landslide body, where the basal slip surface probably had locally convex character. Strike-slip regimes, as well as oblique normal or oblique reverse regimes were observed at the lateral margins of the landslide bodies. The directions of principal stresses could be used as markers of landslide movement directions. Although the multiphase strain indicators were, in general, relatively poorly preserved, the palaeostress analysis revealed several different deformation phases at some landslide parts related to different evolution episodes of the complex landslide. Palaeostress analysis based on the multiple inversion method is an affordable approach for reconstructing stress fields within landslides in soft material. This method is an inexpensive and objective tool for stress field reconstruction even in heterogeneous stress field conditions where the distinction of different faults generations may be impossible.

Detection of ground movements in Montjuïc (Barcelona) using TerraSAR-X data

In this study, 28 StripMap TerraSAR-X images were processed using a Persistent Scatterer Interferometry technique in order to detect and analyze superficial deformation phenomena affecting the hill of Montjuic in Barcelona between December 2007 and November 2009. The results show significant displacement values in two main areas affected by different types of superficial displacements, specifically compaction in a former quarry refill and sliding processes. Displacement values of up to 12 mm/year along the line of sight of the satellite were detected in the area near the Perez de Rozas baseball stadium whereas values of up to 7 mm/year were found in the vicinity of Costa i Llobera gardens. For each deformation area, high resolution deformation velocity data were analyzed and integrated with historical images and field data to interpret the detected phenomena.

Extreme learning machine for the displacement prediction of landslide under rainfall and reservoir level

Landslide prediction is always the emphasis of landslide research. Using global positioning system GPS technologies to monitor the superficial displacements of landslide is a very useful and direct method in landslide evolution analysis. In this paper, an EEMD–ELM model [ensemble empirical mode decomposition (EEMD) based extreme learning machine (ELM) ensemble learning paradigm] is proposed to analysis the monitoring data for landslide displacement prediction. The rainfall data and reservoir level fluctuation data are also integrated into the study. The rainfall series, reservoir level fluctuation series and landslide accumulative displacement series are all decomposed into the residual series and a limited number of intrinsic mode functions with different frequencies from high to low using EEMD technique. A novel neural network technique, ELM, is employed to study the interactions of these sub-series at different frequency affecting landslide occurrence. Each sub-series extracted from accumulative displacement of landslide is forecasted respectively by establishing appropriate ELM model. The final prediction result is obtained by summing up the calculated predictive displacement value of each sub. The EEMD–ELM model shows the best accuracy comparing with basic artificial neural network models through forecasting the displacement of Baishuihe landslide in the Three Gorges reservoir area of China.

Comparison between Differential SAR interferometry and ground measurements data in the displacement monitoring of the earth-dam of Conza della Campania (Italy)

This paper presents the application of Differential Synthetic Aperture Radar (SAR) interferometry (DInSAR) algorithms for the precise monitoring of earth dams ground deformation. The test site selected for this study is the Conza Dam, located in the southern Apennines (Italy), very close to the epicenter of the big earthquake (Mw=6.9) which took place on November 23th, 1980, striking the Irpinia region. Among the multiple advanced DInSAR techniques developed by the SAR community during the last decade, this work uses the so-called SUBSOFT software, developed by the Remote Sensing Laboratory (RSLab) group from the Universitat Politècnica de Catalunya (UPC), which is based on the use of Coherent Pixels Technique (CPT) algorithm. The analysis is carried out using 51 ENVIronmental SATellite-Advanced Synthetic Aperture Radar (ENVISAT-ASAR) images, corresponding to the period from 29th of November 2002 to the 30th of July 2010. In this framework, ground displacements recorded by a network of conventional ground-based sensors are also available for the same temporal span. Indeed, the embankment dam is well instrumented to measure internal settlements by means of cross-arms placed in six different cross-sections, and superficial displacements by means of targets for precise leveling. A statistical analysis has been performed to carry out a better comparison between the measurements obtained with the conventional field sensors and the interferometric data. The high agreement between final DInSAR displacements and in-situ instrumental data, demonstrates the reliability of such technique for the precise monitoring of civil infrastructures, and concretely, in dams with a high exposure factor and its consequent risk.

Plastic and viscous shear displacements of a deep and very slow landslide in stiff clay formation

Deep and superficial displacements have been measured since 2005 in a slow active landslide that has occurred in a stiff clay formation of the Italian Southern Apennines. Recently, new inclinometer casings have been installed to achieve further information on the displacement field. In this paper, standard inclinometer profiles and fixed-in-place probe data are analysed over time. New data confirm previous hypotheses on geometry and kinematics and add more information on the viscous component of displacements. The mechanism of movement, in most of the track, essentially corresponds to sliding localized on a shear surface, consistently with stress and strength distribution. However, locally, internal viscous deformations also occur, especially in the weathered and softened zones of the landslide, and contribute to the soil discharge continuity. Viscous displacements can be interpreted by a simplified rheological model based on the Bingham equation. The residual shear strength has been considered as the creep threshold value and the dynamic viscosity has been considered dependent on the stress level, on the basis of long term direct shear tests under controlled shear stresses which were carried out in laboratory.

METHODOLOGY FOR LANDSLIDE MONITORING IN A ROAD CUT BY MEANS OF TERRESTRIAL LASER-SCANNING TECHNIQUES

Abstract. After the heavy rains of 2009/10 winter, a road cut in the national highway A-44 and the upper slope became unstable; the mass invaded the way and caused important traffic interruptions by several months. The landslide was measured by means of terrestrial laser-scanner techniques and, because of the zone morphology, the used methodology involved scanning the mobilized zone from different stations with several captures from each point. Two scanning campaigns were carried out in a time interval of 14 days. The antenna phase centers were determined by GPS techniques and incorporated to the point clouds as an additional point in the TLS reference system; next, the relative orientation of the different point clouds of each scan station is made, adjusting and merging them in a single point cloud; finally, we proceed to data transformation to a reference system global and common to both campaigns, in which surface and terrain models can be compared. From field data, a digital surface model have been built, and then filtered and edited to have digital elevation models of centimeter spatial resolution. The results obtained by the comparison of models show two rupture zones in the road cut affecting also to the upslope, in which an important volume material flowed with superficial displacements of about 0,55–0,65 m day-1. We also calculated 210 m3 of depleted material and 124,5 m3 of accumulated material; the differences between these volumes (wasting material) are explained because the civil works that were made to clear the road of materials.

Modelling deformation due to a pressurized ellipsoidal cavity, with reference to the Campi Flegrei caldera, Italy

[1] Magmatic unrest can be successfully monitored and studied from modeling of the induced surface deformation; one limiting factor however is the small number of available magmatic source models. Here we have obtained expressions (quadrupole approximation) for displacements and stresses from the inflation of any pressurized triaxial ellipsoid in an infinite elastic medium. The expressions can be evaluated by combining the effects of seven suitable point sources and are approximately valid also for a heterogeneous half-space. Till now, the only available (approximate or exact) expressions for finite expansion sources referred to spheres, prolate spheroids, and horizontal circular cracks embedded in a homogeneous half-space. Our approach allows to model also oblate spheroids and non-axisymmetric sources, whose effects were previously estimable only in the far field through a moment tensor representation. We also show that when the deformation source is a vertically flattened ellipsoid, the inversion of superficial displacements using a general moment tensor may lead to wrong physical models of the deformation source itself. This may be the case for the Campi Flegrei caldera, as well as for other calderas.

Modelling the rainfall-induced mobilization of a large slope movement in northern Calabria

Two recent phases of mobilization of a large, rainfall-induced debris slide are analysed in terms of relationships between rains and phases of displacement. The first activation at San Rocco (San Benedetto Ullano, Calabria) occurred on 28 January 2009, after extraordinary rains had stricken the region for a couple of months. Detailed geomorphologic field surveys, combined with measurements of superficial displacements at datum points, were performed to properly recognize the evolution of the phenomenon. In addition, a real-time control system of rains and superficial displacements measured at extensometers was implemented, to better analyse the evolution of the phenomenon. In early May 2009, the activity reduced to very slow displacements, persisting in the same condition for the following 8 months. On 1 February 2010, premonitory signs of a new phase of activation were noticed, again following 2 months of extraordinary rainfalls. After few days of further precipitations, the middle sector of the landslide activated since 11 February, disrupting the road network and threatening the major lifelines and some buildings. A hydrological analysis aimed at simulating the dates of activation and the main phases of acceleration of the phenomenon was carried out, by calibrating the empirical model FLaIR against the daily rainfalls and the history of known phases of mobilization since 1970. Calibration allowed to successfully simulate both the cited phases of activity of the San Rocco landslide, by predicting the beginning of the movements as well as the following paroxysmal stages, as testified by the measurements at datum points and extensometers. The set of parameters obtained through calibration reflects the influence of both prolonged antecedent rains, and of high-intensity rainfalls of shorter duration, which slightly preceded the major displacements. Once calibrated the model, a suitable threshold could be defined, by analysing the trend of the mobility function against the history of activations of the considered slope movement, and by excluding false alarms. Accordingly, a reliable tool for predicting the phases of activity of a large slope movement could therefore be obtained.

Structure and kinematics of a landslide in a complex clayey formation of the Italian Southern Apennines

This paper describes the geometrical structure and the main kinematic features of an ancient and active landslide which develops in structurally complex formations of the Southern Apennines (Italy): a scaly clayey formation in the medium and lower part of the slope, and a stratified marly–calcareous rock formation in the upper part. The landslide 3D geometry was reconstructed by using topographic data, stratigraphies from continuous coring boreholes and inclinometer data. The analysis of the kinematic features was based on the measurement of deep and superficial displacements. Laboratory tests were carried out to evaluate shear strength parameters. It was found that in each investigated transversal section of the landslide channel the displacements can be considered uniform, and that the decrease of the displacement rates, from upslope to downslope, mostly depends on the increase in the areas of transversal sections, the “soil discharge” variations being slight. Stability analyses confirmed that shear strength close to the residual value is available on the slip surface. The large difference between residual strength and peak strength of the landslide material is consistent with the displacement uniformity.

Monitoring landslide displacements by using ground‐based synthetic aperture radar interferometry: Application to the Ruinon landslide in the Italian Alps

Synthetic aperture radar (SAR) data are collected by a ground‐based radar system forming the synthetic aperture by the sliding of the antennas on a linear rail. Coherent SAR processing converts the raw data into a complex image. The phase of each image pixel contains information on the target‐sensor distance and can be exploited as a ranging tool. The interferometric technique, based on the comparison between paired and coherent SAR images taken at different times, permits the quantitative extraction of this information, thus allowing the monitoring of the morphological changes. The portable device used in this application was developed by the Joint Research Center, Ispra, Italy, specifically for measurements in the field. It is known as Linear SAR, and it is able to provide 17 GHz measurements with a 2.8 m synthetic aperture. A measurement campaign, lasting about 1 week, was performed between July and August 2000 for monitoring superficial displacements at the Ruinon landslide, a 30 million m3 rockslide in the Italian Alps. Two sequences of interferograms are presented and discussed. The interpretation of the sequences has allowed us to derive multitemporal deformation maps of the test area, thus showing the entire displacement field of those landslide sectors characterized by higher radar reflectivity and coherence. Displacement rates up to 1.2 mm h−1 have been measured with a pixel resolution of 5 m and a measurement precision of 0.75 mm. The results have been validated by using ground truth data obtained through automatic extensometers and topographic measurements. Discrepancies are limited to a few millimeters.

Preliminary study of the human lumbar spine using speckle technique. Limits of compression, shear and torsion. Speckle photography--electronic speckle pattern interferometry.

Optical techniques using single wavelength lasers allow precise study of the superficial displacements of deeper anatomical structures through direct mechanical pull. Two techniques have been used in this study: 1. Double exposure speckle photography. Since 1980 the relationship between the surface displacements and minimal traction applied to the transverse processes of the spine, either unilateral or bilateral, was studied in an attempt to simulate muscular action exerted at this level. 2. Computerised speckle interferometry. This allowed analysis of the deformations between the lumbar vertebrae under vertical compression, shear or torsion outside the usual anatomical planes. This preliminary study outlines the mechanical behaviour and the plasticity of the vertebral structures but has been performed on only a few anatomical specimens thus not allowing statistical analysis. This would require a larger series.

Sensitivity and optimization in the determination of deformations by holographic interferometry

The use of a fringe-counting holographic interferometric technique for measuring small superficial displacements can present difficulties in determining the measurement inaccuracy. A useful general method is given here for the analysis of errors in displacement measurements. The optimum number and type of observation directions are determined and correspond to counting in the four semi-diagonals of the holographic plate. The technique, as applied to skull experiments, makes it possible to measure directly displacements of up to 20 μm, in the object plane parallel to the holographic plate. The associated errors range from 0.1–0.3 μm, for a counting inaccuracy of 1 8 – 1 4 of a fringe and increments of traction of 100 g to 1 kg of force.

Analytical method for evaluating superficial fault displacements in volcanic air fall deposits: Case of the Hirayama Fault, south of Tanzawa Mountains, central Japan, since 21,500 years B.P.

The establishment of an analytical method for evaluating superficial fault displacements must contribute greatly to the improvement of methods for earthquake prediction in the Quaternary volcanic areas where many volcanic air fall deposits of known age are widely traceable. However, because the air fall deposits of uniform thickness cover many surfaces of blocks separated by faults, cumulative displacements along faults cannot always be detected in the deposits. Then, the study of geomorphological developments along a fault becomes important in analysis of superficial faults in air fall deposits. The Hirayama fault, south of the Tanzawa mountains, central Japan, is analyzed as an optimal example for studying the methodology in air fall deposits. The most important result of the detailed analysis is that the displacement rate of the Hirayama fault has been decreasing since 21,500 years B.P.; that is, the Hirayama fault has nonuniform history of movement. The result consequently indicates that the assumption of uniform history in fault movement is not always safe in earthquake prediction.