Shear strength of soils containing amorphous clay-size materials in a slow-moving landslide     

Yongshan Wan  James Kwong 《Engineering Geology》2002,65(4):293-303

The shear behavior of soils rich in amorphous clay-size materials was not well reported in the literature. This study analyzed the direct shear and ring shear test data of soil samples containing 55–74% amorphous materials in the clay fraction from a slow-moving landslide in eastern Honolulu, HI. The direct shear test results showed that the undisturbed soil samples when not sheared internally had peak cohesion (c) of about 50 kPa and internal friction angle (Ø) of about 10°. This implies that the amorphous clay-size materials provided strong interparticle bonds for the soils. Breaking of the bonds during the softening process and redistribution of the amorphous clay-size materials were primarily responsible for the drop from the peak strength to the residual strength (c=0, Ø=10° from back calculation with SLOPE/W and c=0, Ø=5–7° from the ring shear test). The drained residual failure envelope is stress dependent due to the interaction of the gel-like amorphous clay-size materials with crystalline silt- and sand-sized particles. The amorphous clay-size materials act as the contact between crystalline particles. The contact increases with increasing consolidation stress, resulting in a decrease in the shear strength and the residual friction angle.  相似文献   

Regolith stripping and the control of shallow translational hillslope failure: application of a two-dimensional coupled soil hydrology-slope stability model, Hawke's Bay, New Zealand     

S. M. Brooks  M. J. Crozier  N. J. Preston  M. G. Anderson 《Geomorphology》2002,45(3-4)

Rainfall-triggered regolith landslides constitute a dominant erosional process in New Zealand hill country. Conversion of forest to pasture about 150 years ago decreased the size of event required to trigger slope failure resulting in greater landslide activity. Recent research indicates that shallow landslides then cause progressive regolith stripping with redeposition at the slope base. The exposed bedrock is less permeable than the pre-existing regolith cover and the redeposited soil has a higher unit weight. Hence, alterations in both hydrological and geotechnical conditions result, changing the triggering thresholds for further failure. In this paper three phases of regolith stripping are investigated using a process-based model, to define variations in both the triggering storms as well as the failure mechanisms under these altered hydrological and geotechnical conditions. Over time, as the regolith is stripped progressively upslope, the threshold for slope failure also changes such that the landscape becomes more stable. However, there is a varying sensitivity to storm type for each of the three phases, which adds complexity to the relationship between regolith stripping and slope failure. Model results suggest different hydrological conditions for slope instability, depending on the degree of stripping and redeposition, adding further complexity. Future advances in process-based modelling are required for detailed investigation of temporal changes in landscape susceptibility to slope failure, and uncertainty in both model parameterisation as well as process representation should be emphasised when applying such models to the long term.  相似文献   

Multi-hazard risk mapping and assessment on an active volcano: the GRINP project at Mount Cameroon   总被引：5，自引：4，他引：1  

Pierre Thierry  Laurent Stieltjes  Emmanuel Kouokam  Pierre Nguéya  Paul M. Salley 《Natural Hazards》2008,45(3):429-456

To help improve the safety of its population faced with natural disasters, the Cameroon Government, with the support of the French Government, initiated a programme of geological risk analysis and mapping on Mount Cameroon. This active volcano is subject to a variety of hazards: volcanic eruptions, slope instability and earthquakes. Approximately 450,000 people live or work around this volcano, in an area which includes one of Cameroon’s main economic resources. An original methodology was used for obtaining the information to reply to questions raised by the authorities. It involves several stages: identifying the different geological hazard components, defining each phenomenon’s threat matrix by crossing intensity and frequency indices, mapping the hazards, listing and mapping the exposed elements, analysing their respective values in economic, functional and strategic terms, establishing typologies for the different element-at-risk groups and assessing their vulnerability to the various physical pressures produced by the hazard phenomena, and establishing risk maps for each of the major element-at-risk groups (population, infrastructures, vegetation, atmosphere). At the end of the study we were able (a) to identify the main critical points within the area, and (b) provide quantified orders of magnitude concerning the dimensions of the risk by producing a plausible eruption scenario. The results allowed us to put forward a number of recommendations to the Cameroon Government concerning risk prevention and management. The adopted approach corresponds to a first level of response to the authorities. Later developments should make it possible to refine the quality of the methodology.  相似文献   

The landslides in the Three Gorges Reservoir Region,China and the effects of water storage and rain on their stability   总被引：5，自引：0，他引：5  

He Keqiang  Li Xiangran  Yan Xueqing  Guo Dong 《Environmental Geology》2008,55(1):55-63

According to the statistics, there were about 1,736 landslides with the total volume of 1.339 × 10¹¹ m³ in the 100 km² area of upper reaches of the Yangtze River, in which about 94% of landslides are triggered by rain and water storage. Thus, based investigation of the results of the landslides in this region, this paper completed a systematic study on the effects of rainfall and water storage on the landslides in the region and found that the distribution of landslides over time and space are well correlated with the precipitation distribution in this region; landslides are also strictly controlled by the stratum, geological structure, river valley form, shore type, etc. Meanwhile, the pattern of water table variation of the three gorges reservoir will do have very serious impacts on the stability of the slopes in this region. All research results show that water storage and rainfall are the two important inducing factors that can cause a lot of large-scale landslides. Therefore, some effective control measures for water storage and rainfall should be taken so as to minimize the impacts of water on the stability of the slopes in the Three Gorges Reservoir Region of Yangtze River, China.  相似文献   

Exploring the magnitude–frequency distribution: a cellular automata model for landslides     

Richard H. Guthrie  Peter J. Deadman  A. Raymond Cabrera  Stephen G. Evans 《Landslides》2008,5(1):151-159

Landslide magnitude–frequency curves allow for the probabilistic characterization of regional landslide hazard. There is evidence that landslides exhibit self-organized criticality including the tendency to follow a power law over part of the magnitude–frequency distribution. Landslide distributions, however, also typically exhibit poor agreement with the power law at smaller sizes in a flattening of the slope known as rollover. Understanding the basis for this difference is critical if we are to accurately predict landslide hazard, risk or landscape denudation over large areas. One possible argument is that the magnitude–frequency distribution is dominated by physiographic controls whereby landslides tend to a larger size, and larger landslides are landscape limited according to a power law. We explore the physiographic argument using first a simple deterministic model and then a cellular automata model for watersheds in coastal British Columbia. The results compare favorably to actual landslide data: modeled landslides bifurcate at local elevation highs, deposit mass preferentially where the local slopes decrease, find routes in confined valley or channel networks, and, when sufficiently large, overwhelm the local topography. The magnitude–frequency distribution of both the actual landslides and the cellular automata model follow a power law for magnitudes higher than 10,000–20,000 m² and show a flattening of the slope for smaller magnitudes. Based on the results of both models, we argue that magnitude–frequency distributions, including both the rollover and the power law components, are a result of actual physiographic limitations related to slope, slope distance, and the distribution of mass within landslides. The cellular automata model uses simple empirically based rules that can be gathered for regions worldwide.  相似文献   

Artificial neural networks and cluster analysis in landslide susceptibility zonation   总被引：14，自引：1，他引：13  

C. Melchiorre  M. Matteucci  A. Azzoni  A. Zanchi   《Geomorphology》2008,94(3-4):379

A landslide susceptibility analysis is performed by means of Artificial Neural Network (ANN) and Cluster Analysis (CA). This kind of analysis is aimed at using ANNs to model the complex non linear relationships between mass movements and conditioning factors for susceptibility zonation, in order to identify unstable areas. The proposed method adopts CA to improve the selection of training, validation, and test records from data, managed within a Geographic Information System (GIS). In particular, we introduce a domain-specific distance measure in cluster formation. Clustering is used in data pre-processing to select non landslide records and is performed on the whole dataset, excluding the test set landslides. Susceptibility analysis is carried out by means of ANNs on the so-generated data and compared with the common strategy to select random non-landslide samples from pixels without landslides. The proposed method has been applied in the Brembilla Municipality, a landslide-prone area in the Southern Alps, Italy. The results show significant differences between the two sampling methods: the classification of the test set, previously separated and excluded from the training data, is always better when the non-landslide patterns are obtained using the proposed cluster sampling. The case study validates that, by means of a domain-specific distance measure in cluster formation, it is possible to introduce expert knowledge into the black-box modelling method, implemented by ANNs, to improve the predictive capability and the robustness of the models obtained.  相似文献   

Representative rainfall thresholds for landslides in the Nepal Himalaya   总被引：14，自引：0，他引：14  

Ranjan Kumar Dahal  Shuichi Hasegawa 《Geomorphology》2008,100(3-4):429-443

Measuring some 2400 km in length, the Himalaya accommodate millions of people in northern India and Pakistan, Nepal, Bhutan, and parts of other Asian nations. Every year, especially during monsoon rains, landslides and related natural events in these mountains cause tremendous damage to lives, property, infrastructure, and environment. In the context of the Himalaya, however, the rainfall thresholds for landslide initiation are not well understood. This paper describes regional aspects of rainfall thresholds for landslides in the Himalaya. Some 677 landslides occurring from 1951 to 2006 were studied to analyze rainfall thresholds. Out of the 677 landslides, however, only 193 associated with rainfall data were analyzed to yield a threshold relationship between rainfall intensity, rainfall duration, and landslide initiation. The threshold relationship fitted to the lower boundary of the field defined by landslide-triggering rainfall events is I = 73.90D^− 0.79 (I = rainfall intensity in mm h^− 1 and D = duration in hours), revealing that when the daily precipitation exceeds 144 mm, the risk of landslides on Himalayan mountain slopes is high. Normalized rainfall intensity–duration relationships and landslide initiation thresholds were established from the data after normalizing rainfall-intensity data with respect to mean annual precipitation (MAP) as an index in which N_I = 1.10D^− 0.59 (N_I = normalized intensity in h^− 1). Finally, the role of antecedent rainfall in causing landslides was also investigated by considering daily rainfall during failure and the cumulative rainfall to discover at what point antecedent rainfall plays an important role in Himalayan landslide processes. Rainfall thresholds presented in this paper are generalized so they can be used in landslide warning systems in the Nepal Himalaya.  相似文献   

Predictive modelling of rainfall-induced landslide hazard in the Lesser Himalaya of Nepal based on weights-of-evidence   总被引：12，自引：0，他引：12  

Ranjan Kumar Dahal  Shuichi Hasegawa  Atsuko Nonomura  Minoru Yamanaka  Santosh Dhakal  Pradeep Paudyal 《Geomorphology》2008,102(3-4):496-510

Landslide hazard mapping is a fundamental tool for disaster management activities in mountainous terrains. The main purpose of this study is to evaluate the predictive power of weights-of-evidence modelling in landslide hazard assessment in the Lesser Himalaya of Nepal. The modelling was performed within a geographical information system (GIS), to derive a landslide hazard map of the south-western marginal hills of the Kathmandu Valley. Thematic maps representing various factors (e.g., slope, aspect, relief, flow accumulation, distance to drainage, soil depth, engineering soil type, landuse, geology, distance to road and extreme one-day rainfall) that are related to landslide activity were generated, using field data and GIS techniques, at a scale of 1:10,000. Landslide events of the 1970s, 1980s, and 1990s were used to assess the Bayesian probability of landslides in each cell unit with respect to the causative factors. To assess the accuracy of the resulting landslide hazard map, it was correlated with a map of landslides triggered by the 2002 extreme rainfall events. The accuracy of the map was evaluated by various techniques, including the area under the curve, success rate and prediction rate. The resulting landslide hazard value calculated from the old landslide data showed a prediction accuracy of > 80%. The analysis suggests that geomorphological and human-related factors play significant roles in determining the probability value, while geological factors play only minor roles. Finally, after the rectification of the landslide hazard values of the new landslides using those of the old landslides, a landslide hazard map with > 88% prediction accuracy was prepared. The methodology appears to have extensive applicability to the Lesser Himalaya of Nepal, with the limitation that the model's performance is contingent on the availability of data from past landslides.  相似文献   

Landslide risk management in Switzerland   总被引：1，自引：2，他引：1  

Olivier Lateltin  Christoph Haemmig  Hugo Raetzo  Christophe Bonnard 《Landslides》2005,2(4):313-320

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Assessment of some spatial and temporal issues in landslide initiation within the Río Aguas Catchment, South–East Spain     

J. S. Griffiths  A. B. Hart  A. E. Mather  M. Stokes 《Landslides》2005,2(3):183-192

A research programme underway in south–east Spain has the overall aim of developing a long-term landscape evolution model for the Tertiary depositional basins that lie within the eastern part of the Betic cordillera. As part of the work it has become apparent that there are multiple natural hazards to development in the region, and the nature and distribution of these is presently under investigation. For one hazard, namely landsliding, a database of over 300 cases has been compiled within one defined 425 km² river catchment, namely the Río Aguas. Evaluation of the database has demonstrated that the contemporary distribution of landslides correlates with areas of steepest slopes across a range of the different lithologies. However, the “slope” component of the landscape is controlled by a wave of incision associated with a river capture event c. 100000 years ago which locally increased erosion by between 5 and 10 times. This event was a function of differential uplift between the depositional basins and resulted in over-steepened slopes within parts of the catchment which have yet to reach equilibrium in this evolving landscape.  相似文献