1,720,974 research outputs found
Coupled hydro-mechanical analysis of the effects of medium depth drainage trenches mitigating deep landslide activity
No full textMitigation measures aimed at reducing the landslide hazard often consists of drainage systems, in particular when the piezometric regime in the slope is identified as an internal factor predisposing the landslide to fail, the latter is very often the case when weather-induced landslides are dealt with. In the past such mitigation measure has been considered eligible solely for shallow landslide mechanisms. However, some authors have reported that the variation in piezometric regime at large depth becomes no more negligible if a medium depth drainage trench system is installed. Nonetheless, the efficacy of a drainage trench system is often hard to quantify because of the high-level computation process that needs to be undertaken, since it has to include, in principle, several parameters describing the saturated-partially saturated hydro-mechanical behaviour of the material as well as all the processes occurring when interacting with the vegetation and the weather; this is even more complicated due to the geological history and the resulting geo-hydro-mechanical (GHM) context to deal with. As such, the determination of the efficiency of a drainage system represents still an open issue in the engineering practice, since this issue relates to a transient hydro-mechanical (HM) boundary value problem. Very often the design of such mitigation measures has been pursued by using design-charts determined under simplified hypotheses. In this paper, the effects of implementing the geological history of the slope of reference, representative of a widely spread landslide mechanism type across the GHM context dealing with, have been investigated on the drains-induced transient seepage, being computed by means of advanced fully coupled two-dimensional HM numerical modelling. The HM numerical analyses reported in this contribution address to a reference case study in the Eastern sector of the Southern Apennines region, which has been selected as prototype landslide in the assessment of the stabilization efficacy of deep drainage trench systems
Analysis of the slope-vegetation-atmosphere interaction for the design of the mitigation measures of landslide risk in clayey slopes
No full textL’attività di ricerca affrontata dal dottorando riguarda l'evoluzione delle condizioni di equilibrio nel tempo in riferimento alla stabilità di frane clima-indotte. L'approccio seguito è principalmente legato al confronto tra analisi numeriche e dati di monitoraggio di campo, che sono di fondamentale importanza per poter determinare la veridicità delle previsioni numeriche.
La ricerca mira innanzitutto ad identificare i principali fattori interni ed esterni da considerare per il replicare correttamente numericamente, le evidenze sul campo. Come tale in questa fase del lavoro, lo scopo è quello di diagnosticare l'attuale attività stagionale osservata ricorrentemente e documentata in un caso di studio (la frana di Pisciolo) tramite monitoraggi di sito. Attraverso strategie numeriche diverse e gradualmente più complesse si è effettuato un calcolo del processo franoso. In particolare, sono state condotte analisi numeriche idrauliche e idromeccaniche, volte a mettere in luce i punti di forza e di debolezza di ciascuna strategia numerica nella modellazione dell’attività attuale della frana in studio.
La rappresentatività del pendio di Pisciolo con riferimento a diversi meccanismi di frana nell'Appennino sud-orientale, rende questo caso di particolare interesse, poiché le conclusioni sito-specifiche sono valide anche per casi di studio meno studiati, o meno monitorati.
Questa circostanza è molto rilevante, dal momento che consente una trasposizione di concetti e strategie di progettazione dal caso specifico (la frana di Pisciolo) ad altri casi di studio, anche senza studi dettagliati sito-specifici.
L'obiettivo finale di questo lavoro di ricerca è di fornire consigli per quanto concerne due diverse strategie di mitigazione; in particolar modo il dottorando si è occupato della progettazione di sistemi di allerta e di interventi di bioingegneria in relazione al meccanismo di frana di riferimento.
Il sistema di allerta è progettato con riferimento a diversi corpi di frana, da superficiale a profondo, evidenziando le differenze sia per quanto riguarda le variabili di soglia di riferimento sia che i valori di soglia. Questa analisi viene effettuata me-diante modellazione numerica idraulica seguita dal calcolo del fattore di sicurezza con il metodo del limite di equilibrio.
L'input forzante climatico per queste analisi è ottenuto da dati climatici reali, dal 2001 al 2016, per i quali sono disponibili precipitazioni e temperature minime e massime da annali climatici forniti da una stazione di monitoraggio climatico vicina al versante di Pisciolo. I risultati della diagnosi del meccanismo di frana consentono di comprendere che anche la condizione climatica preesistente può influire sul successivo risultato di un certo input climatico. Di conseguenza tra tutti gli anni monitorati disponibili, sono stati scelti due anni diversi come rappresentativi di uno molto piovoso e di uno molto secco; questi sono stati applicati prima dell'applicazione dell'anno climatico in esame.
L'analisi dell'efficienza di un intervento di ingegneria naturalistica o di bioingegneria è stata anch’essa analizzata in questa attività di ricerca; in particolare, è stato effettuato uno studio preliminare sull'uso di colture radicate sul suolo per la stabilizzazione di corpi superficiali e profondi.
A questo scopo, un campo prova (circa 2000 m2) è stato allestito al piede del meccanismo franoso di Pisciolo, allo scopo di determinare l'efficienza idraulica di alcuni piante selezionate. I vari tipi di colture sono stati seminati nell’area del test e il monitoraggio delle variabili climatiche, dello stato di copertura superficiale (zona insatura) e dello stato del suolo più profondo (zona saturata) è iniziato a gennaio 2018 ed è tuttora in corso.
Una piattaforma numerica di equazioni differenziali per risolvere il numerica-mente il calcolo termo-idraulico è stato descritto, con lo scopo futuro di calcolare in maniera inversa i flussi verso l’atmosfera evaporativi e traspirativi indotti dalle piante.
Pur non essendo conclusivo, questo studio può essere scientificamente rilevante, ed è quindi auspicabile che esso abbia ripercussioni sul lato pratico, risultando utile per future linee guida per la progettazione di interventi di bioingegneria simili a quello in studio.The present research activity deals with the evolution of the equilibrium conditions in time with reference to climate-induced landslides. The approach followed herein is mainly linked to the comparison between numerical analyses and field monitoring data which are of major importance to state the success of the numerical predictions.
The research is first aimed at identifying the main internal and external factors to be accounted for numerically replicating the field evidence. As such in this step of the work, the purpose is to diagnose the current seasonal activity observed in a case study (the Pisciolo slope) in terms of hydraulic and mechanical behavior. In particular, a boundary value problem has been numerically solved with different and gradually more complex numerical strategies. Specifically, hydraulic and hydro-mechanical numerical analyses have been carried out, aimed at highlighting the strengths and weaknesses of each numerical strategy in modeling the current activity of the Pisciolo slope.
The representativeness of the Pisciolo slope with respect to several landslide mechanisms in the South-Eastern Apennine, makes this case study of particular interest, since the site-specific conclusions drawn may be also valid for other mechanisms.
This circumstance appears to be very relevant, since it allows for transposition of concepts and design strategies from a representative slope to others, even without very detailed site-specific studies.
The final aim of this research work is to give advice on two different mitigation measures, addressing the design of early warning systems and bio-engineering interventions for the landslide mechanism of reference.
The early warning system is designed with reference to different landslide bodies, from shallow to deep, highlighting the differences on both the reference threshold variables and threshold values. This analysis is carried out by means of hydraulic numerical modeling followed by the computation of the safety factor with the limit equilibrium method.
The climatic forcing input for these analyses is obtained from real climatic data, from 2001 to 2016, for which rainfall and minimum and maximum temperatures were available from climatic annals provided by a climatic monitoring station close the Pisciolo slope. The results of the diagnosis of the landslide mechanism allow realizing that also the pre-existent climatic condition may affect the subsequent impact of a certain climatic input. As such, among all the monitored years available, two different years have been chosen as representative of a very rainy and a very dry one; those have been applied prior the application of the climatic year under investigation.
The analysis of the efficiency of a bio-engineering intervention has been of interest in this research activity; in particular, the use of deep-rooted crops on the soil cover for stabilizing shallow and deep bodies is studied herein.
As such, a test site (approx. 2000 m2) has been installed at the toe of the Pisciolo landslide, aimed at determining the hydraulic efficiency of some selected crop types. The various crop types have been seeded into the test site, and the monitoring of climatic variables, the shallow cover state (unsaturated zone), and the deeper soil state (saturated zone) has been activated in January 2018 and is still on-going.
A numerical platform of differential equations for solving the thermo-hydraulic boundary value problem is described, with the future aim to back-calculate the upward fluxes of evaporation and plant-induced transpiration.
Although not being conclusive, this study may be scientifically relevant and is then intended to have repercussions on the practical side, being useful for future guidelines for the design of bio-engineering interventions
The Effects of Slope Initialization on the Numerical Model Predictions of the Slope-Vegetation-Atmosphere Interaction
Full text linkDeep slope movements and, eventually, slope failure, have been often interpreted to be due to slope-vegetation-atmosphere interaction on slopes formed of clayey materials in the Italian Southern-Eastern Apennines, as reported in the literature. Such slopes are generally formed of flysch, within which clay is the main lithotype. Such clays are characterized by a disturbed meso-fabric, as an effect of the intense tectonics. The paper presents the results of coupled hydromechanical numerical analyses of the slope-vegetation-atmosphere interaction for a clay slope representative for the geomechanical scenario where such climate-induced deep slope movements have been repeatedly recorded. In the analyses, different model initialization procedures and parameter values were adopted. The comparison of the numerical results with the site data is aimed at assessing the effects of the soil-vegetation-atmosphere interaction taking place in the top strata of the slope, on the stress-strain conditions across the whole slope, and on the slope stability. The comparison between the numerical results of the analyses carried out entailing different initialization stages are intended to evaluate the influence of such a stage on the model predictions. It is found that only when the slope model initialization accounts for the slope loading history, developed over geological time, the numerical predictions get close to the site observations. In such case, the numerical results confirm that deep movements consequent to progressive failure may take place in clay slopes due to the slope-vegetation-atmosphere interaction
Numerical Back-Analysis of In-Situ Constant Head Tests in Partially Saturated Soil Cover to Determine the Permeability Function
No full textReinterpreting the Bishop’s Parameter in the Light of the Drying Collapse of Clays: From Phenomenology to Numerical Implementation
No full textNumerical modelling of geological processes as means for the diagnosis of ancient landslide mechanisms
No full textThe occurrence of deep paleo-landslides in marine clays is a well-documented phenomenon in multiple slopes within the south-eastern Italian Apennines and their associated foredeep basin. To accurately diagnose the mechanisms occurring in such landslides, a comprehensive numerical simulation of the processes leading to the initial slope failures is essential. This approach is only feasible when the geological history of the soil deposit has been meticulously evaluated. This paper presents a methodological procedure adopted to assist in diagnosing the current activity of a slow-moving, deep-seated ancient landslide using hydro-mechanical modelling. To investigate the processes leading to the initial slope failures, elasto-plastic finite element simulations have been conducted. These simulations aim to replicate the geological processes that the slope has experienced, which are identified as the key contributors to the landslide's inception. The application of this numerical modelling procedure has proven to be a valuable diagnostic tool, enhancing the understanding of the ancient landslide mechanism and providing insights into its current features, such as the position of the toe, landslide depth, and style of movement
Assessing the influence of the hydraulic boundary conditions on clay slope stability: The Fontana Monte case study
No full textRecent studies have assessed that slope-vegetation-atmosphere, SLVA, interaction may trigger the activity of
deep landslides in clayey slopes. In some cases, the presence of an underground aquifer, fed by an upstream
hydraulic recharging area, may represent a predisposing factor of such activity, being co-responsible of deep
piezometric heads, which can undergo seasonal fluctuations due to the SLVA interaction. In this perspective, the
present paper illustrates the results of a scientific research, carried out in a pilot site of the Daunia Apennines, the
Fontana Monte slope at Volturino (Foggia, Italy), considered as a prototype of the class of landslide mechanisms
controlled by both the rainfall water infiltration and the presence of a water-bearing aquifer in the hillslope.
Numerical simulations of the saturated/partially saturated transient seepage flow in the slope have been
performed by means of uncoupled hydraulic finite element analyses, with the aim of investigating the sources of
large piezometric heads, related to climatic, hydrogeological and hydraulic slope features. The rainfall and
evapotranspiration fluxes, the latter defined through the FAO Penman-Monteith method, are both implemented
as ground surface input, while seasonal variations of the upstream hydraulic boundary conditions are imposed to
predict the seasonal piezometric excursion at shallow and deep monitoring points. The transient seepage results
are then used as input for limit equilibrium analyses to assess the influence of the hydraulic settings on the
stability of the considered landslide body. The work shows the impact of both climatic and hydraulic factors on
the seepage processes, affecting the stability of the slope. Moreover, it is highlighted that the accurate imple-
mentation of the upstream hydraulic feeding is fundamental for a reliable prediction of the monitored piezo-
metric regime, strictly related to the recharge of the water-bearing aquife
Geo-hydro-mechanics for quantitative landslide hazard assessment (QHA)
No full textLandslide risk represents a strong limitation to the social and economic development of civil society
in chain areas. This is particularly the case in highly urbanized regions. The need for mitigation of landslide risk
prompts landslide hazard mapping. The aim of the research work presented in the paper is the use of geo-hydromechanics for the assessment of landslide hazard from the site to the small scale. The geo-hydro-mechanical
analysis of landslide hazard is first presented to diagnose single slope. To this aim, the procedure for the
deterministic analyses of the internal/external slope factors and of the possible landslide processes bringing
about instability is presented. The contribution offers an overview of the key steps of the deterministic procedure
with the phenomenological interpretation of a landslide mechanism as first, and the numerical validation
thereafter. A representative case study of application of the methodology is discussed. The case study is
representative for chain slopes in the Italian Apennines and exemplifies the geo-hydro-mechanical diagnosis of
landslide hazard in complex geological contexts. As second, a methodology for intermediate to regional scale
landslide hazard assessment, based on geo-mechanical interpretations, is also recalled. The methodology is the
Multiscalar Method for Landslide Mitigation, MMLM (Cotecchia et al. 2016b; Cafaro et al. 2016). It uses the
hydro-mechanical diagnoses of landsliding at the slope scale as reference starting point. In this contribution, a
brief example of the validation of the MMLM to the geologically complex Daunia-Lucanian Apennines (Italy) is
also show
Analysis of climate-driven processes in clayey slopes for early warning system design
No full textThe activity of deep landslides in slopes formed of clayey turbidites has been observed to be connected to the climatic regime in the Mediterranean, based on field data and phenomenological interpretations. With the aim of investigating this connection, the effects of the soil-vegetation-atmosphere interaction on the piezometric regime were investigated by means of hydraulic finite-element analyses of the transient seepage across a prototype clayey slope. The ground surface condition was defined accounting for rainfall and evapotranspiration flux, estimated through the United Nations' Food and Agriculture Organization Penman-Monteith approach. The predicted excursions of the piezometric head within the slope over time were found to agree with field observations. The predicted piezometric profiles were investigated to evaluate the infiltration processes during the year and show how these bring about seasonal piezometric excursions. The results of the hydraulic analyses were then input into limit equilibrium analyses to assess the impact of the slope-vegetation-atmosphere interaction on the stability of landslide bodies of different depths. The results show how such impact depends on the stratigraphy of the slope. Furthermore, the variability of the climatic precursor of landsliding with landslide depth was characterised to guide the design of early warning systems for mitigation purposes
An Investigation into the Water Retention Behaviour of an Unsaturated Natural Fissured Clay
No full textThe presence of intensely fissured soils is often found to relate to high geotechnical risks, such as landslide risk. This is especially the case of the Southern Apennines, Italy, where slopes formed of intensely fissured clays are frequently affected by landslides. The latter are generally triggered by rainfall infiltration, which takes place through the outcropping, unsaturated clayey soil cover. With the final aim of reducing landslide risk in areas covered by fissured clays, a detailed hydro-mechanical characterisation of these materials is required. While the behaviour of fully saturated fissured clays has been investigated in the last decade, only a few studies dealing with unsaturated, natural fissured clays are reported in the literature. The present paper aims to give a contribution toward filling this gap by extending an investigation campaign started a few years ago on the Paola Doce fissured clay outcropping on the Pisciolo slope (Southern Apennines, Italy). The physical properties of the material and some of its key micro- to meso-structural features are first analysed, the latter also based on Scanning Electron Microscope (SEM) micrographs of an undisturbed sample taken at 1.4 m depth on the Pisciolo slope, which is mainly formed of Paola Doce clay. Subsequently, water retention data of the soil are presented, which were obtained using both high-capacity tensiometers and the filter paper technique. These data were collected not only on undisturbed samples but also while subjecting the same material to drying paths. The results herein reported aim to make a link between the water retention behaviour of the Paola Doce clay sampled at Pisciolo and its fissured structure
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