physically based and distributed approach to analyze rainfall triggered landslides at watershed scale abstract landslides are a serious threat to life and property throughout the world the causes of landslides are various since multiple dynamic processes are involved in driving slope failures one of these causes is prolonged rainfall which affects slope stability in different ways water infiltrating in a hillslope may cause a rise of the piezometric surface which in turn involves an increase of the pore water pressure and a decrease of the soil shear resistance for this reason knowledge of spatio temporal dynamics of soil water content infiltration processes and groundwater dynamics is of considerable importance in the understanding and prediction of landslides dynamics in this paper a spatially distributed and physically based approach is presented which embeds a slope failure method in a hydrological model the hydrological model here used is the tribs model triangulated irregular network real time integrated basin simulator that allows simulation of most of spatial temporal hydrologic processes infiltration evapotranspiration groundwater dynamics and soil moisture conditions that can influence landsliding slope stability is assessed by implementing the infinite slope model in tribs the model based on geotechnical and geomorphological characteristics classifies each computational cell as unconditionally stable or conditionally stable soil moisture conditions resulting from precipitation can trigger landslides at conditionally stable locations when a landslide occurs the model also computes the amount of detached soil and its possible path downslope model performance has been initially tested on a small catchment with very steep slopes located in the northern part of sicily italy after a sensitivity analysis concerning some model parameters

instability of saturated and unsaturated coarse granular soils abstractit is well known that saturated silt and fine sand are susceptible to instability during undrained shearing coarse granular soils may also be unstable during undrained shearing or during rainfall infiltration starting at an unsaturated state this paper investigates the instability of three saturated and unsaturated granular soils with different fines contents f 50 32 and 10 isotropic consolidation tests and mercury intrusion porosimetry tests were first conducted to investigate the instability of the microstructures of these granular soils then drained and undrained triaxial tests were conducted to investigate the instability behavior under the saturated condition subsequently wetting tests under the constant shear stress condition were carried out on unsaturated specimens to investigate the instability of the same soils during water infiltration the instability in the microstructures is in accordance with the compressibility of the soils the instability during undrained shearing under

a physically based model for the topographic control on shallow landsliding a model for the topographic influence on shallow landslide initiation is developed by coupling digital terrain data with near surface through flow and slope stability models the hydrologic model topog o loughlin 1986 predicts the degree of soil saturation in response to a steady state rainfall for topographic elements defined by the intersection of contours and flow tube boundaries the slope stability component uses this relative soil saturation to analyze the stability of each topographic element for the case of cohesionless soils of spatially constant thickness and saturated conductivity the steady state rainfall predicted to cause instability in each topographic element provides a measure of the relative potential for shallow landsliding the spatial distribution of critical rainfall values is compared with landslide locations mapped from aerial photographs and in the field for three study basins where high resolution digital elevation data are available tennessee valley in marin county california mettman ridge in the oregon coast range and split creek on the olympic peninsula washington model predictions in each of these areas are consistent with spatial patterns of observed landslide scars although hydrologic complexities not accounted for in the model e g spatial variability of soil properties and bedrock flow control specific sites and timing of debris flow initiation within areas of similar topographic control

reassessing the quality of sea ice deformation estimates derived from the radarsat geophysical processor system and its impact on the spatiotemporal scaling statistics we reassess the trajectory tracking errors inherent to the lagrangian deformation estimates with a new propagation of uncertainty derivation and show that previous formulations applied to deformation estimates from the radarsat geophysical processor system rgps were either too low due to a simplistic formulation or too high due to incorrect assumptions in the derivation we show that when the resulting signal to noise ratios are used to discriminate the deformation estimates based on their quality as done for buoy records the spatio temporal scaling exponents for the mean total deformation rate increase especially at smaller scale such that a space time coupling of the scaling which is otherwise absent emerges from the rgps deformation data set in accord with previous analyses performed with buoy observations we also show that the pre processing method used to reduce the effects of irregular sampling of the lagrangian deformation fields can significantly impact the value of the deformation statistics and could possibly explain part of previous discrepancies between deformation statistics obtained with buoy records and large scale sar imagery specifically we show that spurious lines of deformation appear when interpolating rgps trajectories presenting temporal sampling inconsistencies in the context of using observed sea ice deformation statistics to constrain and improve the performance of sea ice models high confidence in the observed deformation field statistics is necessary using appropriate well documented methods to derive the set of statistics to be reproduced by models therefore becomes crucial

assessment of rainfall induced shallow landslide susceptibility using a gis based probabilistic approach abstract this study proposes a probabilistic analysis method to assess shallow landslide susceptibility over an extensive area by integrating an infinite slope model with gis geographic information system and monte carlo simulation taking into consideration the inherent uncertainty and variability in input parameters the mechanical parameters of soil materials such as cohesion and friction angle used in the infinite slope analysis have been identified as the major source of uncertainty because of their spatial variability therefore these parameters were considered as random variables in this probabilistic landslide analysis to properly account for the uncertainty in input parameters the probabilistic analysis method used was monte carlo simulation the process was carried out in a gis based environment because gis has effective spatial data processing capacity over broad areas in addition the hydrogeological model was coupled with the infinite slope model to evaluate increases in pore water pressure caused by rainfall the proposed approach was applied to a practical example to evaluate its feasibility the landslide inventory map and the spatial database for input parameters were constructed in a grid based gis environment and a probabilistic analysis was implemented using monte carlo simulation to evaluate the performance of the model the results of the probabilistic landslide susceptibility analysis were compared with the landslide inventory the probabilistic approach demonstrated good predictive performance when compared with the landslide occurrence location in addition deterministic analysis was carried out using fixed single input data for comparison with the results from the proposed approach in this comparison the probabilistic analysis showed better performance than the deterministic analysis in addition the results showed that proper consideration and understanding of uncertainties play an important role in accurately predicting shallow landslide susceptibility

shallow landslides in pyroclastic soils a distributed modelling approach for hazard assessment an effective assessment of shallow landslide hazard requires spatially distributed modelling of triggering processes this is possible by using physically based models that allow us to simulate the transient hydrological and geotechnical processes responsible for slope instability some simplifications are needed to address the lack of data and the difficulty of calibration over complex terrain at the catchment s scale we applied two simple hydrological models coupled with the infinite slope stability analysis to the may 1998 landslide event in sarno southern italy a quasi dynamic model barling et al 1994 was used to model the contribution to instability of lateral flow by simulating the time dependent formation of a groundwater table in response to rainfall a diffusion model water resour res 36 2000 1897 was used to model the role of vertical flux by simulating groundwater pressures that develop in response to heavy rainstorms the quasi dynamic model overestimated the slope instability over the whole area more than 16 but was able to predict correctly slope instability within zero order basins where landslides occurred and developed into large debris flows the diffusion model simulated correctly the triggering time of more than 70 of landslides within an unstable area amounting to 7 3 of the study area these results support the hypothesis that both vertical and lateral fluxes were responsible for landslide triggering during the sarno event and confirm the utility of such models as tools for hazard planning and land management

determination of shear strength of hawaiian residual soil subjected to rainfall induced landslides the determination of shear strength parameters for the stability analysis of rainfall induced landslides requires both a knowledge of the stress history and a laboratory simulation of the failure stress path of the soil involved such soils exist on steep slopes and have experienced a highly anisotropic stress action through which they have been consolidated a series of tests has been carried out on residual soil from a steeply sloping site in hawaii typical of locations subject to rainfall induced landslides two types of tests were carried out anisotropicconsolidation undrained acu tests which mimic field consolidation stress paths of the soil and constant shear stress drained csd tests which best simulate the failure stress path for rainfall induced landslides substantial differences of soil behaviour in csd tests and acu tests are recognized the csd strength parameters are considered most appropriate for analysing the rainfall induced landslides typical csd derived parameters are o y 32

transient deterministic shallow landslide modeling requirements for susceptibility and hazard assessments in a gis framework abstract application of transient deterministic shallow landslide models over broad regions for hazard and susceptibility assessments requires information on rainfall topography and the distribution and properties of hillside materials we survey techniques for generating the spatial and temporal input data for such models and present an example using a transient deterministic model that combines an analytic solution to assess the pore pressure response to rainfall infiltration with an infinite slope stability calculation pore pressures and factors of safety are computed on a cell by cell basis and can be displayed or manipulated in a grid based gis input data are high resolution 1 8 m topographic information derived from lidar data and simple descriptions of initial pore pressure distribution and boundary conditions for a study area north of seattle washington rainfall information is taken from a previously defined empirical rainfall intensity duration threshold and material strength and hydraulic properties were measured both in the field and laboratory results are tested by comparison with a shallow landslide inventory comparison of results with those from static infinite slope stability analyses assuming fixed water table heights shows that the spatial prediction of shallow landslide susceptibility is improved using the transient analyses moreover results can be depicted in terms of the rainfall intensity and duration known to trigger shallow landslides in the study area

a distributed slope stability model for steep forested basins a distributed physically based slope stability model dslam based on an infinite slope model a kinematic wave groundwater model and a continuous change vegetation root strength model is presented it is integrated with a contour line based topographic analysis and a geographic information system gis for spatial data extraction and display the model can be run with either individual rainfall events or long term sequences of storms these inputs can be either actual storm records or synthesized random events based on monte carlo simulation the model is designed to analyze rapid shallow landslides and the spatial distribution of safety factor fs in steep forested areas it can investigate the slope stability problem in both temporal and spatial dimensions for example the impact of timber harvesting on slope stability either at a given time or through an extended management period the probability of landslide occurrence for a given year and the delivery of landslide sediments to headwater streams the dslam model was applied in a steep forested drainage of cedar creek in the oregon coast ranges using actual spatial patterns of timber harvesting and measured rainfall during a major storm which triggered widespread landslides in that area in 1975 simulated volume and number of failures were 733 m3 and 4 respectively these values agreed closely with field measurements following the 1975 storm however the effect of parameter uncertainty may complicate this comparison for example when soil cohesion values of 2 0 and 3 0 kpa were used the failure volume changed by factors of 2 04 and 0 41 respectively compared with the average condition of 2 5 kpa used in the simulation for soil depths 30 higher and lower than the standard condition the failure volume changed by factors of 2 0 and 0 27 respectively when maximum root cohesion changed from 12 5 kpa average condition to 10 kpa the failure volume increased 1 73 fold for the case of 15 kpa the failure volume changed by a factor of 0 55 the simulated failures caused by the storm were mostly in hollows the simulations show that the spatial distribution of fs is controlled mainly by topography and timber harvesting patterns and is greatly affected by groundwater flow patterns during major rainstorms most areas with fs 3 0 corresponded with the distribution of blocks clear cut in 1968 and all elements with fs 2 0 were in areas clear cut in 1968 areas with low fs 1 0 1 6 expanded dramatically during the rainstorm and decreased at a slow rate after the storm factors of safety in hollows declined sharply during the storm

stability analyses of rainfall induced landslides the slope stability issues concerning rainfall induced slope failures are investigated and presented specifically the effect of both negative and positive pore water pressures on the stability of initially unsaturated slopes are carefully explained and coupled with infinite slope analysis methods in order to present a predictive formulation of slope failures that occur as a result of rainfall events the formulation serves as a baseline analysis method for evaluating potentially unstable soil slopes that are subject to surface infiltration and explains the various triggering mechanisms that may occur based on individual combinations of the slope geometry soil strength and infiltration parameters a procedural method is outlined for utilizing the analytical formulation to predict the change in the factor of safety for a slope subject to infiltration and a detailed analysis of a case study is presented to verify the method quantitative statements are made concerning the time and depth of failure in relationship to the soil slope and rainfall parameters

on the evaluation of unsaturated flow in a natural slope in rio de janeiro brazil abstract geotechnical engineers and geologists are frequently concerned with the complex phenomenon of rainstorm induced landslides in mountainous tropical regions this paper analyses the hydrological conditions that contributed to a huge deep seated slide of a slope in rio de janeiro brazil the slope failure occurred after a short period of intense rainfall buried cars and caused structural damages to an adjacent building on the following day the failure surface was completely saturated despite the fact that no groundwater was observed within the slope understanding a rain induced landslide is a considerable challenge in the present case there was an extra question to be answered why were no slope movements observed a few months earlier when a more intense rainfall reached the slope geological and geotechnical surveys were carried out aiming at determining complete soil profile characterization piezometric levels and hydraulic parameters field investigations indicated a variable thickness unsaturated residual soil layer overlying a gneissic rock the transition between the saprolitic soil and the sound rock consisted of a highly fractured and weathered rock 3d flow modelling has shown that the amount of rain infiltration was insufficient to produce positive pore water pressures it was likely that development of preferential infiltration paths could explain the hydrological conditions of the slope during landslide water infiltration through the fractured soil rock transition induced a rapid development of positive pore water within the soil mass this favourable scenario might have been created by the lack of maintenance of the crest drainage channel adjacent to the slide area it is a common engineering practice to try to associate rainfall amounts to the risk of slope failure the role that bedrock plays in generating pore pressure is seldom considered the numerical analyses presented in this paper pointed out at the complexity of flow modeling of rain infiltration through unsaturated residual soil slopes it essentially revealed that flow mechanisms other than rain infiltration over the slope surface might play a major role on hydrological pattern of slopes

causative mechanisms of rainfall induced fill slope failures slope failures in fill slopes formed by loosely compacted completely decomposed granite in hong kong occur commonly during intense tropical rainstorms the stress path greatly influences the shear strength of the soil mass and is therefore crucial to the identification of slope failure mechanisms the soil mass in this case is largely unsaturated in situ hydrologic response to rainstorms indicates that soil suction is reduced by rainfall infiltration which often becomes the triggering factor in initiating slope instability the constant dead load tests on unsaturated loosely compacted completely decomposed granite appropriately simulate the field stress path of rainfall induced fill slope failure by reducing suction the tests indicate that matric suction contributes to the dilative or contractive behavior of the unsaturated soils the anisotropically consolidated undrained triaxial tests demonstrate the consistently contractive behavior of the specimens on this basis we delineate the in situ stress conditions leading to the initiation of rainfall induced fill slope failure and the stress paths of the transformation from local failures to flowage based on a systematic study of fill slope case records in hong kong implications of such mechanisms on fill slope stability are given

behavior of coarse widely graded soils under low confining pressures colluvial soils are usually coarse and widely graded shallow seated failures occur frequently in colluvial soil deposits duringrain fallinfiltration thispaperinvestigatesthebehaviorofcoarse widelygradedsoilsunderverylowconfiningpressuresof5e25 kpa encountered in shallow seated failures isotropic consolidation tests drained triaxial tests and undrained triaxial tests were conducted on several widely graded soils with different coarse contents but with the same void ratio of 0 62 with increasing coarse content the soil microstructure changes froma fines controlledstructuretoacoarse controlledstructureafteracriticalcoarsecontentofapproximately70 siltysandwithgravelwith acoarsecontentclosetothecriticalvalueexhibitsthehighestcompressibilitybecauseofthepresenceoflargeinteraggregatepores evenunder very low confining pressures such soil still shows strong contractive behavior during drained loading and generates large positive pore water pressures during undrained loading this explains why shallow seated failures occur frequently in colluvial soil deposits caused by rainfall infiltration soilswithlowerorhighercoarsecontentsthanthecriticalvaluemayshowdilativebehaviorunderthesamelowconfiningpressures the critical statefriction angle increases with thecoarse content doi 10 1061 asce gt 1943 5606 0000755 2013american society of civil engineers ce database subject headings coarse grained soils compression landslides microstructure shear strength soil compaction soil pressure

prediction of landslide susceptibility using rare events logistic regression a case study in the flemish ardennes belgium abstract in this article a statistical multivariate method i e rare events logistic regression is evaluated for the creation of a landslide susceptibility map in a 200 km2 study area of the flemish ardennes belgium the methodology is based on the hypothesis that future landslides will have the same causal factors as the landslides initiated in the past the information on the past landslides comes from a landslide inventory map obtained by detailed field surveys and by the analysis of lidar light detection and ranging derived hillshade maps information on the causal factors e g slope gradient aspect lithology and soil drainage was extracted from digital elevation models derived from lidar and from topographical lithological and soil maps in landslide affected areas however we did not use the present day hillslope gradient in order to reflect the hillslope condition prior to landsliding the pre landslide hillslope was reconstructed and its gradient was used in the analysis because of their limited spatial occurrence the landslides in the study area can be regarded as rare events rare events logistic regression differs from ordinary logistic regression because it takes into account the low proportion of 1s landslides to 0s no landslides in the study area by incorporating three correction measures the endogenous stratified sampling of the dataset the prior correction of the intercept and the correction of the probabilities to include the estimation uncertainty for the study area significant model results were obtained with pre landslide hillslope gradient and three different clayey lithologies being important predictor variables receiver operating characteristic roc curves and the kappa index were used to validate the model both show a good agreement between the observed and predicted values of the validation dataset based on a qualified judgement the created landslide susceptibility map was classified into four classes i e very high high moderate and low susceptibility if interpreted correctly this classified susceptibility map is an important tool for the delineation of zones where prevention measures are needed and human interference should be limited in order to avoid property damage due to landslides

characteristics of earthquake and rain induced landslides near the epicenter of wenchuan earthquake abstract numerous landslides were triggered by the 12 may 2008 wenchuan earthquake in china particularly near the epicenter during the rainy season in 2010 after the earthquake much of the landslide debris was reactivated causing a large number of fatalities the earthquake has a significant impact on the subsequent rain induced landslides based on interpretation of satellite images taken in 2008 and 2010 combined with yearly field investigations this paper attempts to 1 map the earthquake induced landslides near the epicenter 2 present the distribution of the landslides occurring during a subsequent extreme storm in the same area and 3 compare the distribution characteristics of the earthquake induced landslides and the rain induced landslides through this study the following findings were obtained 1 the internal relief of the landslides in the study area is much higher than that in other affected regions of the wenchuan earthquake zone 2 the landslide area in hard rocks i e the granite and diorite zones is much larger than that in alluvium 3 the volume of hill slope loose deposits decreased while the volume of channel deposits increased during the process of mass transportation caused by rainfall after the earthquake 4 during the rainy seasons after the earthquake the density of landslides increased while the area of landslides decreased significantly and the type of landslides transformed from debris slides to debris flows and 5 the rain induced landslides are less steeper than the earthquake induced landslides

a warning system for rainfall induced shallow failures abstract it is widely recognised that soil slips and debris flows are triggered by short intense storms owing its geologic geomorphologic and climatic settings the piedmont region nw italy is highly prone to the occurrence of this kind of landslides in the last two centuries in fact a total of 105 severe meteoric events which triggered shallow failures occurred and of these 18 events took place from 1990 to 2002 a fair number of rainfall thresholds have been proposed in the literature defined both on empirical or on physical bases empirical thresholds are defined collecting rainfall data for landslide meteoric events and for events without landslides while physical thresholds are based on numerical models that consider the relation between rainfall pore pressure and slope stability the main objective of this paper is the identification of the empirical triggering thresholds for the piedmont region four meteoric events were selected and analysed november 4 5 1994 july 7 8 1996 april 27 30 2000 october 13 16 2000 because they supply a wide range of variation for both rainfall parameters duration intensity cumulative rainfalls and the number of induced landslides in the intensity duration plot the critical limit is described by the equation i 19d 0 50 where i rainfall intensity expressed in mm h and d rainfall duration expressed in hours such a limit is traced to envelop 90 of the points on the graph in the ni d diagram the triggering thresholds are given by the equations ni 0 76d 0 33 and ni 4 62d 0 79 where ni normalised intensity with respect to the annual precipitation map expressed in mm h pma 100 in the article the different meaning of these thresholds is discussed finally the diagram ni ncr is proposed the triggering threshold is given by the expression ni 0 09ln ncr 0 54 where ncr is the normalised cumulative critical rainfall mm pma 100 the application of the triggering thresholds as a fundamental element in a warning system dedicated to the safeguarding of population in landslide prone areas is discussed in detail an operating procedure which is presently being verified and tested in the studied area is described

a physically based distributed cell model for predicting regional rainfall induced shallow slope failures abstract rainfall induced slope failures are one of the most frequent hazards on hilly terrains this paper proposes a physically based distributed cell model to predict regional rainfall induced shallow slope failures in two layer soils under realistic rainfall conditions the model consists of four components namely a digital terrain model a spatial rainfall distribution model an infiltration analysis model and a slope stability and reliability evaluation model the digital terrain is discretized into a grid of numerous cells first with the properties of the soils in each cell assigned universal kriging is then adopted to interpolate the spatial rainfall distribution afterwards the infiltration analysis model is used to analyze the infiltration process in two layer soils under realistic rainfall conditions the slope stability and reliability evaluation model is finally adopted to assess the regional slope stability and reliability the distributed cell model is applied to evaluate the spatial and temporal response of a 164 5 km2 area to rainfall near the epicenter of the 2008 wenchuan earthquake zone comparison between the predicted and observed slope failures triggered by the 13 august 2010 storm shows that this model is capable of predicting the locations of rainfall induced slope failures reasonably well the model is intended for use as a module in a real time warning system for rainfall induced slope failures

infiltration analysis to evaluate the surficial stability of two layered slopes considering rainfall characteristics abstract shallow slope failures in residual soil during periods of prolonged infiltration are common throughout the world using a one dimensional infiltration model and an infinite slope analysis this study examines an approximate method of determining how infiltration influences the surficial stability of two layered slopes the method extends moore s infiltration model which is based on the green ampt model to cover more general situations including those where water moves upward from a perched water table in decreasingly permeable soil the method has also been used to evaluate the likelihood of a shallow slope failure being induced by a particular rainfall event in making this evaluation the method takes into accounts the rainfall intensity and duration of various return periods in a two layered soil profile a comparison of the results of the infiltration model with the results of numerical analyses shows that with the use of properly estimated input parameters the proposed model compares reasonably well with other model that rely on more rigorous finite element method

spatial probabilistic modeling of slope failure using an integrated gis monte carlo simulation approach spatial probabilistic modeling of slope failure using a combined geographic information system gis infinite slope stability model and monte carlo simulation approach is proposed and applied in the landslide prone area of sasebo city southern japan a digital elevation model dem for the study area has been created at a scale of 1 2500 calculated results of slope angle and slope aspect derived from the dem are discussed through the spatial interpolation of the identified stream network the thickness distribution of the colluvium above tertiary strata is determined with precision finally by integrating an infinite slope stability model and monte carlo simulation with gis and applying spatial processing a slope failure probability distribution map is obtained for the case of both low and high water levels