Evaluation of failure of slopes with shaking-induced cracks in response to rainfall

Centrifuge model tests on slopes subject to shaking and rainfall have been performed to examine the response of slopes with shaking-induced cracks to subsequent rainfall and evaluate the corresponding landslide-triggering mechanisms. The failure pattern of the slope subject to shaking and then rainfall was found different from that of the slope subject to only rainfall. When shaking caused cracks on the slope shoulder and rupture line below, the mobilized soil slid along the slip surface that extended to the rupture line, the main crack became the crown of the undisturbed ground once the slope was subject to a subsequent rain event, and the progression of the landslide was related to the rainfall intensity. During the landslide caused by light rainfall, the main scarp kept exposing itself in the vertically downward direction while the ground behind the main crack in the crack-containing slope remained undisturbed. The detrimental effect of cracks on soil displacement was more evident when the slope was exposed to heavy post-shaking rainfall, resulting in a rapid and massive landslide. Additionally, the volume of displaced material of the landslide, the main scarp area on the upper edge, and the zone of accumulation were larger in the crack-containing slope subject to heavy rainfall, in comparison with those in the crack-free slope. The deformation pattern of slopes with shaking-induced cracks during rainfall was closely related to rainfall intensity and the factor of safety provided a preliminary estimation of slope stability during rainfall. Moreover, even when subjected to the same rainfall, the slopes with antecedent shaking-induced cracks displayed different levels of deformation. The slope that experienced larger shaking had greater deformation under the following rainfall, and the shaking-induced slope deformation also controlled the slip surface location. Finally, the velocity of rainfall-induced landslide could be greatly influenced by the prior shaking event alone. Despite being under light rainfall, the slope that has encountered intense previous shaking exhibited an instant landslide.

Short-term geomorphological evolution of the Poggio Baldi landslide upper scarp via 3D change detection

On 19 March 2010, a 4 million m3 landslide occurred at Poggio Baldi, a small village in the Santa Sofia municipality, central Apennines (Forlì-Cesena, Italy). The landslide caused severe damages to some homes and obstructed both the SS310 national road and the Bidente river. The Poggio Baldi landslide arose in the “Marnoso-Arenacea Romagnola” formation composed of a pelitic-arenaceous turbiditic sequence. The landslide was classified as a rotational landslide, evolving into a partially confined flow-like landslide and causing the reactivation of the deposit of a previous landslide that took place in 1914. This paper reports a study of the phenomena currently occurring on the 100-m high main scarp of this landslide complex. The aim of the study was to assess ground changes that occurred on the upper scarp from 2015 to 2018 and to infer a preliminary evolutionary model capable of supporting short-term landslide scenarios. For this purpose, multi-station terrestrial laser scanner surveys were performed in 2015, 2016, 2017, and 2018. Additionally, an unmanned aerial vehicle three-dimensional photogrammetric survey was carried out in 2016. Analyses of the three-dimensional digital models of the main scarp made it possible to carry out several exhaustive multi-temporal investigations and to derive a detailed three-dimensional change detection scheme for it. The results showed an active geomorphological evolution of the rock scarp area due to frequent rockfalls and topples (of the order of a few m3), with significant local volume changes (a few thousand m3/year) and with potential implications for the long-term evolution of the entire slope.

Landslide site delineation from geometric signatures derived with the Hilbert–Huang transform for cases in Southern Taiwan

Landslides are a frequently occurring threat to human settlements. Along with global climate change, the occurrence of landslides is the forecast to be even more frequent than before. Among numerous factors, topography has been identified as a correlated subject and from which hillslope landslide-prone areas could be analyzed. Geometric signatures, including statistical descriptors, topographic grains, etc., provide an analytical way to quantify terrain. Various published literature, fast Fourier transform, fractals, wavelets, and other mathematical tools were applied for this parameterization. This study adopts the Hilbert–Huang transform (HHT) method to identify the geomorphological features of a landslide from topographic profiles. The sites of the study are four “large-scale potential landslide areas” registered in the government database located in Meinong, Shanlin, and Jiasian in southern Taiwan. The topographic mapping was conducted with an airborne light detection and ranging instrument. The resolution of the digital elevation model is 1 m. Each topographic profile was decomposed into a number of intrinsic mode function (IMF) components. Terrain characterization was then performed with the spectrum resulting from IMF decomposition. This research found that the features of landslides, including main scarp-head, minor scarp, gully, and flank, have strong correspondence to the features in the IMF spectrum, mainly from the first and the second IMF components. The geometric signatures derived with HHT could contribute to the delineation of the landslide area in addition to other signatures in the terrain analysis process.

Topographic Analysis of Landslide Distribution Using AW3D30 Data

Landslides cause serious damage to society, and some occur as reactivations of old landslides in response to earthquakes and/or rainfall. Landslide distributions are therefore useful when siting engineering projects such as road and tunnel constructions. Although several methods have been proposed to extract landslides from topographic data on the basis of their morphological features (crown, main scarp, and main body), such morphological features are gradually eroded by heavy precipitation or landslide recurrence. Therefore, conventional methods cannot always identify areas influenced by recurrent landslides. In this study, we investigated the relationship between ridgeline continuity and landslide distribution using AW3D30, which is a global digital surface model (DSM) dataset produced from the Panchromatic Remote-sensing Instrument for Stereo Mapping (PRISM) onboard the Advanced Land Observing Satellite (ALOS) launched by the Japan Aerospace Exploration Agency (JAXA) in 2013. The relationship between the area of landslides and the number of ridge pixels was analyzed, and we propose a method for estimating the upper bound distribution of landslide topographies based on extracted ridgelines data using the Data Envelopment Analysis (DEA) function on the R statistical software packages. The upper bound on the area of landslides decreases as the number of ridge pixels increases. The same trend was seen in all the five sites, and the upper bound derived from one site is hardly exceeded by those derived from all other sites. By using the upper bound distribution function, the landslide distribution will not be missed.

Multidisciplinary studies of the Puigcercós historical landslide in the Catalan Pyrenees

<p>More than a century ago, the Puigcercós village located in the region of Pallars Jussà (Catalonia, Spain), suffered a large-scale landslide that occurred on January 13th, 1881. More than 5 million m<sup>3</sup> of sediments and rocks were displaced and a 200 m long and 25 m high rock scarp was formed. Luckily, during the main event, the nearby village was not affected, and due to a prompt evacuation and re-location of the entire village, no casualties were reported. Nevertheless, consequent retreat of the main scarp did destroy the big part of the old village, which confirmed not only the necessity for its relocation, but also gave one of the first clearly described and confirmed examples of a successful geologic risk prevention.</p><p>During the last decade, the members of the RISKNAT-UB group have chosen this site to conduct pilot studies of rockfalls and landslides using a multidisciplinary approach. The utilized observational techniques include Terrestrial Laser Scanner (TLS), photogrammetry, GPS, seismic monitoring and geophysical prospecting techniques. The work presented here is an overview of these activities, including the main milestones of the ongoing research. Special emphasis will be given to the use of geodetic techniques for investigating changes on the depositional area of the landslide and around the crown cracks at the upper level of the main scarp. As a result of the GPS observations, for the first time, 130 years after the occurrence of the event, it was possible to observe a continuing geomorphological activity of the depositional zone of this historical landslide, Currently, the RISKNAT-UB group operates cost-effective, high-resolution and low-cost photogrammetric instruments and seismic continuous records at the site, in order to monitor the evolution of the Puigcercós rock scarp. The correlation of the seismic and the photogrammetric data and intermittently obtained LiDAR images enables us to monitor and characterize frequent rockfalls and premonitory deformations occurring at the site. These observations have allowed quantifying the rate of retreat of the rock scarp at a rate of 10 to 11 cm/yr and a slow motion of the depositional zone up to 6 mm/yr. Since the geologic risk at the study area is not significant, due to the absence of population and/or infrastructures, this site is an ideal natural laboratory for developing new observational techniques, which can be used to develop early warning systems for rockfalls and landslides.</p><p>The authors would like to acknowledge a financial support from CHARMA (CGL2013-40828-R) and PROMONTEC (CGL2017-84720-R AEI/FEDER, UE) projects, financed by the Spanish MINEICO. We are also thankful to UNESCO Global Geopark Conca de Tremp-Montsec for their support.</p>

Using RPAS derived images and LiDAR DEM's for the assessment of geomorphic changes in a cultural heritage site affected by recent landslides

<p>The recent advances in the acquisition of aerial images using Remotely Piloted Aircraft Systems (RPAS) offer an efficient and low-cost solution for the assessment of geomorphologic changes in areas affected by landslides, gullies and rill erosion, river channel migration, through the creation of accurate Digital Elevation Models (DEM's). Despite many advantages of DEM's obtained through Structure from Motion (SfM) method (resources, availability, high resolution - spatial and temporal), they are suitable for reduced study areas, usually under 100-200 ha, where there is a significant intensity of geomorphic processes and where their effects threaten human assets or heritage.<br>This study focus on the area of Poiana Mănăstirii Thraco-Getic fortress (2550-2050 yr BP), located in the central part of Moldavian Plateau, Romania. Covering a surface of 12 ha, the fortress is surrounded by a 2-3 m high wall, with a 10 m wide base, and a 1 m deep and 4-6 m wide trench. In its southern part, the landslides destroyed these remnants, and due to the deforestation of the slope in the last 30 years, these processes recorded almost yearly reactivations. The main landslide scarp is affected by a gully system that contributes to the archaeological site degradation.<br>A DJI Phantom 4 Pro UAV was flown over the study area in October 2019 and acquired images with 80 % side and forward overlap at 20 MP resolution. Visual SFM open source software was used to obtain the point cloud and for georeferencing, a Ground Control Point network was measured with a Trimble GeoExplorer 6000 GPS. In order to detect and to map geomorphic changes, LiDAR point clouds (2012) were used as a reference dataset (with a spatial resolution of 0.25 m, and a vertical accuracy of 0.13 m).<br>A detailed map showing the changes in topography between 2012 and 2019 has been carried out, supplementing a geomorphological mapping. The most dynamic portions of the landslide are accompanied by dense micro-topographic features like secondary scarps, longitudinal and transversal cracks, which have been mapped using the ortophotoimage. The most dynamic parts of the hillslope are an earthflow, shallow and slumps along with the eastern gully system, piping sinkholes, and the main scarp gullies. The evolution of the landslides and gullies indicate that the southern part of the fortress will be affected in the near future. Alongside the identification of the most active parts of the landslide, we conclude that the entire recently deforested area must return as quick as possible to the initial land use (forest).</p>

English-Ukrainian landslide terminology

The interaction between scientific schools in different countries should begin with revision of terminology in the specified science branch and correlation of interpretation, meaning of terms, such as, in Ukrainian and in English. The causes of difficulties of English-Ukrainian landslide terminology are considered in the article, in particular, the different traditions of defining a landslide as a phenomenon, the different degrees of detailing if we talk about the morphological elements and mechanisms of their movement, and the different approaches to criteria of landslides and other hillslope processes classification in regulatory documents (in Ukraine there are ДБН DBN – The State Norms of Construction, and ДСТУ DSTU – The State [Technical] Standards of Ukraine), especially the restricted quantity of suggested terms among them. However, the authors should use the broader terminology to adequately reflection of the Ukrainian researches results in English. For this purpose, a short glossary about six dozen of English terms divided into five thematic blocks (material, movement, surfaces, parts of a landslide, and other structures and smaller forms) is compiled. Several neologisms have been proposed: боковина [bokovyna] – a flank (as a flank of landslide according to D. M. Cruden’s definition (1993): the undisplaced material next to the sides of the rupture surface), маргінальна межа [marhinalʹna mezha] – a toe (by D. M. Cruden’s definition (1993), the lower, usually curved margin of the displaced material of a landslide). It is also suggested using the word верхів’я [verkhivya] as a term, and it means the crown – the practically undisplaced material still in place and adjacent to the highest parts of the main scarp of the landslide. We did not find any English matching to some elements of the landslide, such as брівка головного уступу [brivka holovnoho ustupu] – the contact line between the crown surface and the main scarp surface; зсувні тераси [zsuvni terasy] – terrace-like upper surfaces of the slump blocks; підошва зсуву [pidoshva zsuvu] – the undisturbed or slightly disturbed areas adjacent to the toe of the landslide; ложе зсуву [lozhe zsuvu] – the surface of undisturbed soils and rocks (although there are different meanings of this term). Sometimes a right or left side of the rupture surface is included to the meaning of flank, but in Ukrainian tradition, the term борт зсуву [bort zsuvu] does not contain the undisplaced material adjacent to the sides of the rupture surface. In general, many questions remain, first, a correlation between the landslide classification in the Ukrainian and foreign traditions, so we invite you to continue the discussion about terminology and difference in the meaning or interpretation of terms. Key words: landslides, terminology, Ukrainian, English.

Hydrodynamic and Soil Biodiversity Characterization in an Active Landslide

Landslides are common in the Northern Apennines (Italy) and their resulting changes in soil structure affect edaphic fauna biodiversity, whose activity has concurrent impacts on soil structural stability and water-holding capacity. The aim of this study was to characterise landslide evolution and assess potential relationships between its hydrogeological features and soil fauna. The landforms of the study area, located in the River Taro valley, were mapped and the hydraulic head fluctuations and groundwater electrical conductivity profiles were measured. The soil arthropod community was studied in seven sites, one subject to earth flow and six to rotational slide; the last ones were divided into the main scarp of the slide, and five sites characterized by different land use: three grassland, a wheat cultivated field and an overgrown area. Soil organic matter (SOM) and pH measurements were performed. Hydrogeological results suggest unexpected rapid percolation of relatively low-salinity waters through the unsaturated zone. Both lower SOM content and arthropod biodiversity were found in earth flow area, while higher values were found in grasslands. Fauna composition appears to be a good indicator of soil degradation processes, linked to the hydraulic features, and contributes to the evaluation of the soil condition in landslide areas for further agricultural purposes.

Susceptibility to Translational Slide-Type Landslides: Applicability of the Main Scarp Upper Edge as a Dependent Variable Representation by Reduced Chi-Square Analysis

The applicability of main scarp upper edge (MSUE) as dependent variable representation was performed in a translational slide susceptibility zonation of the Milia and Roglio basins, Italy. Two landslide inventories were built thanks to detailed geomorphological mapping and aerial photograph analysis. The landslides were used to create the models before 1975, while those after 1975 were employed to validate the predictive power of the model. Possible landslide-related factors were chosen from a geomorphological survey. The inventory landslide maps and the landslide-related factor maps were processed by conditional analysis, producing landslide susceptibility maps with five susceptibility classes. A comparison between the distribution of landslides after 1975 and those derived from models provided the predictive power of each model, which in turn was used to define the best predictive model. Reduced chi-square analysis allowed to define the efficiency of MSUE as dependent variable representation. MSUE can be applied as dependent variable representation to landslide susceptibility zonation with appreciable results. In the Roglio basin, slope angle, distance from streams, and from tectonic lineaments proved to be the main controlling factors of translational slides, whereas in the Milia basin, lithology and slope angle gave more satisfactory results as landslide-predisposing factors.

Hydrographic And Hydrochemical Characteristics of the Landslide Lake Jazerske (Spišska Magura, Northern Slovakia)

This article presents the hydrographic and hydrochemical characteristics of this lake. Lake Jazerske is located in the Western Carpathians (Spiš Magura) in northern Slovakia. It occupies a depression that was formed at the foot of the main scarp of a landslide. Below the lake, there are small intercolluvial depressions that have been transformed into wetlands (peat bogs). The studied lake is very small. Its area is 3600 m2 and its length is 85 m. The maximum depth of the lake is 7.2 m and its capacity is 17 000 m3. The lake is supplied by an inflow of groundwater via fractured aquifers. During periods of heavy rainfall and snow melting, the lake is also supplied by the water from surface runoff. On the main slope of the landslides, traces of ephemeral courses were also found. During the periods of increased supply (spring snow melting, summer rainfall), the outflow of water from the lake occurs both on the surface and underground. In terms of its hydrochemistry, the lake water represents the four-ion type - bicarbonate-sulphate-calcium-magnesium. The concentrations of various ions is characteristic of the shallow groundwater of the Carpathian flysch. The predominant cation, the average concentration of which is 52 mg dm-3, is calcium. The dominant anion is carbohydrates with an average concentration of 163 mg dm-3. What is interesting is the very low levels of chlorides, which do not exceed 2 mg dm-3. The electrolytic conductivity of the water flowing out of the lake ranged from 290 to 328 μS cm-1.