Soil Thickness Spatial Distribution Influence on Factor of Safety Equation (original) (raw)
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Soil Science Society of America Journal, 2008
This study compared the centrifuge and pressure plate methods with appropriate run durations. Samples collected in tropical soils located in Brazil along a 10-km local hydrosequence across the Cerrado-Amazonia transition (Set 1) and along a 350-km regional toposequence across the Cerrado region (Set 2) were selected to compare and discuss statistically the similarity of the soil water retention recorded by using the pressure plate and centrifuge methods. The results showed good agreement (R 2 = 0.99) for the 1:1 comparison of measured pointwise soil water content values (Set 1) as well as for the fitted soil water content curves by the van Genuchten model using data points obtained with the two methods (Set 2). Thus, the centrifuge method should be considered as an appropriate method for determining soil water retention properties not only because of similar results with the pressure plate method but also because it is much less time consuming.
2018
This paper presents a three-step approach to evaluate and map mass movement risk. First, hazard and vulnerability, the two components of mass movement risk, are evaluated through the use of a Weighted Product Method (WPM) borrowed to the MultiAttribute Utility Theory (MAUT). The model evaluates each potential action a A (set of potential actions) according to a set of attributes, points of view and criteria i, i = 1, ..., n, from gi measurement scales. The criteria retained are environmental factors of susceptibility to landslides and surrounding elements at risk (stakes). In a second phase, the risk is estimated by the product of its two components. Finally, the spatial mass movement risk is determined by crossing the susceptibility (hazard) and consequences (vulnerability) maps. The method has been tested in the area of Aїn el Hammam in the basin of Tizi-Ouzou (Algerian Tell).
Large scale debris-flow hazard assessment: a geotechnical approach and GIS modelling
Natural Hazards and Earth System Science, 2003
A deterministic distributed model has been developed for large-scale debris-flow hazard analysis in the basin of River Vezza (Tuscany Region -Italy). This area (51.6 km 2 ) was affected by over 250 landslides. These were classified as debris/earth flow mainly involving the metamorphic geological formations outcropping in the area, triggered by the pluviometric event of 19 June 1996. In the last decades landslide hazard and risk analysis have been favoured by the development of GIS techniques permitting the generalisation, synthesis and modelling of stability conditions on a large scale investigation (>1:10 000). In this work, the main results derived by the application of a geotechnical model coupled with a hydrological model for the assessment of debris flows hazard analysis, are reported. This analysis has been developed starting by the following steps: landslide inventory map derived by aerial photo interpretation, direct field survey, generation of a data-base and digital maps, elaboration of a DTM and derived themes (i.e. slope angle map), definition of a superficial soil thickness map, geotechnical soil characterisation through implementation of a backanalysis on test slopes, laboratory test analysis, inference of the influence of precipitation, for distinct return times, on ponding time and pore pressure generation, implementation of a slope stability model (infinite slope model) and generalisation of the safety factor for estimated rainfall events with different return times.
Landslides are important natural hazard in Turkey especially in Black Sea Region considering the economic damages and life loss. Sinop city enlarge through hillslope areas with its increasing population. The study area is located in Demirciköy Watershed approximately 11 km southwest of Sinop city centre which embodies several landslides. The aim of the work presented in this paper is to propound a new index representing the deterministic part of the landslide susceptibility phenomenon in terms of FSI (factor of safety index) under dynamic soil saturation conditions. SMDR (Soil Moisture Distribution and Routing) model is employed to simulate the dynamic soil saturation variations utilizing with the monthly mean meteorological data. The calculated dynamic factor of safety is transformed to the FSI with the use of a statistical evaluation known as likelihood ratio method. The ultimate landslide susceptibility maps obtained with the new proposed method indicate that deterministic approach produce fairly acceptable results in terms of physical explanation of landslide existence. On the other hand, spatiotemporal evaluation of the landslide susceptibility concept augment the accuracy comparing with the conventional landslide susceptibility concept according to the produced high performance and satisfactory results.
Simulations of landslide hazard scenarios by a geophysical safety factor
Natural Hazards, 2013
Soil response to rainfall is a complex phenomenon that requires modeling of many sources of heterogeneity, whose variations can be relevant on various timescales and whose precise description requires a large amount of data inputs. Due to the great complexity of the problem, many simplifying assumptions are usually made in modeling landslides triggered by rainfall. As regards rainfall-induced shallow landslides, conventional approaches base slope stability analyses on the infinite slope model combined with hydrological models, which provide the time evolution of groundwater pressure head and volumetric water content. On the other hand, the response of geophysical quantities to water changes depends also on the variations in mechanical and hydrological properties. For this reason, we attempt a different approach to the problem of slope stability assessment by shifting the focus on the analysis of variations in geophysical properties. In this paper, starting from experimental resistivity data acquired in a test area, we perform a series of numerical simulations to study how changes in soil resistivity spatial distributions may affect the size of unstable areas. We use a simple cellular automaton whose states are defined by the values of a local and time-dependent geophysical factor of safety, which depends on soil electrical resistivity and slope inclination. We studied the probability of occurrence of rainfall-induced shallow landslide events by driving the system to instability through a decrease in electrical resistivity values. Numerical simulations are performed by varying number and intensity of the applied perturbations. Hazard scenarios obtained by in situ distributions of resistivity values are compared with those coming from initial random distributed resistivity values. Our results suggest possible critical rates of resistivity changes for triggering instability in the investigated area and point out the crucial role of resistivity variations in prediction of larger events.
Estimation of debris flow critical rainfall thresholds by a physically-based model
Hydrology and Earth System Sciences Discussions, 2012
Real time assessment of debris flow hazard is fundamental for setting up warning systems that can mitigate its risk. A convenient method to assess the possible occurrence of a debris flow is the comparison of measured and forecasted rainfall with rainfall threshold curves (RTC). Empirical derivation of the RTC from the analysis of 5 rainfall characteristics of past events is not possible when the database of observed debris flows is poor or when the environment changes with time. For landslides triggered debris flows, the above limitations may be overcome through the methodology here presented, based on the derivation of RTC from a physically based model. The critical RTC are derived from mathematical and numerical simulations based on the 10 infinite-slope stability model in which land instability is governed by the increase in groundwater pressure due to rainfall. The effect of rainfall infiltration on landside occurrence is modelled trough a reduced form of the Richards equation. The simulations are performed in a virtual basin, representative of the studied basin, taking into account the uncertainties linked with the definition of the characteristics of the soil. A large number 15 of calculations are performed combining different values of the rainfall characteristics (intensity and duration of event rainfall and intensity of antecedent rainfall). For each combination of rainfall characteristics, the percentage of the basin that is unstable is computed. The obtained database is opportunely elaborated to derive RTC curves. The methodology is implemented and tested on a small basin of the Amalfi Coast (South 20 Italy).
Hydrological Processes, 2008
This paper describes a coupled, distributed, hydrological-geotechnical model, GEOtop-FS, which simulates the probability of occurrence of shallow landslides and debris flows. We use a hydrological distributed model, GEOtop, which, models latent and sensible heat fluxes and surface runoff, and computes soil moisture in 3-D by solving Richards'equation numerically, together with an infinite-slope geotechnical model, GEOtop-FS. The combined model allows both the hydraulic and geotechnical properties of soil to be considered and realistically modelled. In particular, the model has been conceived to make direct use of field surveys, geotechnical characteristics and soil moisture measurements. In the model the depth of available sediments is also used to characterize the hydraulic properties of the area examined.To account for the uncertainty related to the natural variability in the factors influencing the stability of natural slopes, the safety factor is computed with a probabilistic approach. In order to determine the likelihood of slope failures, soil parameters are assigned distributions instead of single deterministic values.The analysis presented was carried out for an alpine watershed, located in the Friuli region, Italy, for which some geological and geotechnical data were available. In the past, this watershed experienced landslides and debris flows during intense storms following long and moderate intensity rainfall events. The distributed coupled GEOtop-FS model was calibrated by reproducing some of these events and validated in order to map future failure probabilities. Copyright © 2007 John Wiley & Sons, Ltd.
E&S Engineering and Science
The present study investigated the susceptibilities to mass movements of slopes in areas classified as having high potential for natural accidents in Viçosa-MG-Brazil. Several stability scenarios were analyzed based on the geological-geotechnical characteristics of the terrain, considering resistance parameters and geometry for a two-dimensional analysis in the Geostudio Slope/W software. The research was based on an urban susceptibility map, which allowed the selection of areas with high potential for mass movement to carry out the PMT tests. These, in turn, subsidized the followed by numerical stability simulations to identify the degree of instability and the safety factor of the area in question. The PMT test was chosen for its speed and precision in obtaining the soil parameters in depth, which, associated with stability simulations, allowed an assessment of the slopes. In addition, scenarios were evaluated with geotechnical parameters obtained and the confidence interval was v...
A methodology for estimating risks associated with landslides of contaminated soil into rivers
2014
Urban areas adjacent to surface water are exposed to soil movements such as erosion and slope failures (landslides). A landslide is a potential mechanism for mobilisation and spreading of pollutants. This mechanism is in general not included in environmental risk assessments for contaminated sites, and the consequences associated with contamination in the soil are typically not considered in landslide risk assessments. This study suggests a methodology to estimate the environmental risks associated with landslides in contaminated sites adjacent to rivers. The methodology is probabilistic and allows for datasets with large uncertainties and the use of expert judgements, providing quantitative estimates of probabilities for defined failures. The approach is illustrated by a case study along the river Göta Älv, Sweden, where failures are defined and probabilities for those failures are estimated. Failures are defined from a pollution perspective and in terms of exceeding environmental quality standards (EQS) and acceptable contaminant loads. Models are then suggested to estimate probabilities of these failures. A landslide analysis is carried out to assess landslide probabilities based on data from a recent landslide risk classification study along the river Göta Älv. The suggested methodology is meant to be a supplement to either landslide risk assessment (LRA) or environmental risk assessment (ERA), providing quantitative estimates of the risks associated with landslide in contaminated sites. The proposed methodology can also act as a basis for communication and discussion, thereby contributing to intersectoral management solutions. From the case study it was found that the defined failures are governed primarily by the probability of a landslide occurring. The overall probabilities for failure are low; however, if a landslide occurs the probabilities of exceeding EQS are high and the probability of having at least a 10% increase in the contamination load within one year is also high.
This work presents the new model called CRHyME (Climatic Rainfall Hydrogeological Modelling Experiment), a tool for the geo-hydrological hazard evaluation. CRHyME is a physically based and spatially distributed model written in Python language and represents an extension of the classic hydrological models that simulate inflows-outflows at the basin scale. A series of routines have been integrated to describe the phenomena of geo-hydrological instabilities such as the triggering of shallow landslides as well as debris flows, catchment erosion, and sediment transport into the river. These phenomena are generally decoupled with respect to the continuous hydrological simulation while in CRHyME they are quantitatively and simultaneously evaluated through a multi-hazard approach. CRHyME has been tested on some case studies located in Italian basins. Valtellina and Emilia's areas were considered for the calibration and validation procedures of the model thanks also to the availability of literature data concerning past occurred geo-hydrological instability phenomena. Calibration and validation of the model conducted on presented case studies have been assessed through some hydrological indexes such as NSE (Nash-Sutcliffe Efficiency) and RMSE (Root Mean Square Error) while for landslide phenomena the ROC (Receiver Operating Characteristic) methodology was applied. CHRyME has been able to: 1) reconstruct the surface runoff at the reference hydrometric stations located at the outlets of the basins, 2) estimate the solid transport at some hydropower reservoirs compared to the reference data, and 3) evaluate the triggering of shallow landslides and debris flows compared to those recorded in the literature. The ranking has shown a rather good performance of the model in terms of numerical conservativity of water and solid balances, revealing suitable not only for back-analysis studies but also as an efficient tool for Civil Protection multi-hazard assessment. 1 Introduction Landslides, floods, and debris flows represent serious geo-hydrological hazards in mountain environments (Gariano and Guzzetti, 2016). Shallow landslides and debris flows are often the result of soil erosion and sediment transport (Brambilla et