Three-dimensional mapping of a landslide using a multi-geophysical approach: the Quesnel Forks landslide

A landslide located on the Quesnel River in British Columbia, Canada is used as a case study to demonstrate the utility of a multi-geophysical approach to subsurface mapping of unstable slopes. Ground penetrating radar (GPR), direct current (DC) resistivity and seismic reflection and refraction surveys were conducted over the landslide and adjacent terrain. Geophysical data were interpreted based on stratigraphic and geomorphologic observations, including the use of digital terrain models (DTMs), and then integrated into a 3-dimensional model. GPR surveys yielded high-resolution data that were correlated with stratigraphic units to a maximum depth of 25 m. DC electrical resistivity offered limited data on specific units but was effective for resolving stratigraphic relationships between units to a maximum depth of 40 m. Seismic surveys were primarily used to obtain unit boundaries up to a depth of >80 m. Surfaces of rupture and separation were successfully identified by GPR and DC electrical resistivity techniques.     

The chaotic characteristics of landslide evolution: a case study of Xintan landslide

A new method based on the chaos theory is used to assess the evolution process of a slope system. The method is applied to the Xintan landslide and the results show: (1) the slope movement is a complex process of the slope going in and out of the stable and chaotic state; (2) the method reveals the evolution process of the slope pointing to the slope failure while the observed movement shows a simple monotonic increase with time; (3) the method is not sufficiently mature to precisely predict the time of failure but it has potential for improvement with further research and more field data for analysis.     

Permanent seismic deformation analysis of a landslide

A failed slope may not necessarily require a remedial treatment if it can be shown with confidence that the maximum movement of the slide mass will be within tolerable limits, i.e., not cause loss of life or property. A permanent displacement analysis of a landslide for static and seismic conditions is presented using a continuum mechanics approach. Computed values of displacement for static conditions compare favorably with field measurements and computed values of seismic displacements for a postulated earthquake motion appear reasonable. Also, the seismic displacements using the continuum mechanics approach compare favorably with those obtained using the Newmark sliding block procedure for assessing seismically-induced slope deformations.     

Prediction on landslide displacement using a new combination model: a case study of Qinglong landslide in China

Prediction on landslide displacement plays an important role in landslide early warning. Many models have been proposed for this purpose. However, the accuracy of the prediction results by these models often varies under different conditions. Rational evaluation and comprehensive consideration of these results still remain a scientific challenge. A new comprehensive combination model is proposed to predict the landslides displacement. The elementary displacement prediction is made by the support vector machine model, the exponential smoothing model, and the gray model (GM)(1,1). The results of the models are comprehensively evaluated by combining the results and introducing the accuracy matrix. The optimal weight in the evaluation work is obtained. A rational prediction result can be attained based on the so-called combination model. The proposed method has been tested by the application of Qinglong landslides in Guizhou Province, China. The comparison between the prediction results and in situ measurement shows that the prediction precision of the proposed model is satisfactory. The root-mean-square error (RMSE) of the combination model can be reduced to 1.4316 (monitoring site JCK2), 1.2623 (monitoring site JCK4), 2.3758 (monitoring site JCK6), 2.2704 (monitoring site JCK8), 1.4247 (monitoring site JCK11), and 0.9449 (monitoring site JCK12), which is much lower than the RMSE of the individual models.

     

一种黄土滑坡渐进破坏过程分析

在中国西北,建设了许多灌溉水渠,由于水渠的灌溉引起了许多滑坡破坏,并带来了人员伤亡和财产损失。以高楼村水渠灌溉引起的黄土滑坡破坏为例,提出了滑坡破环渐进过程为：水的入渗在滑体中产生一定深度的水压力,引起黄土黏聚力和摩擦角下降,使滑坡体在一定深度产生剪破坏,紧接着滑体后缘产生拉剪破坏,致使后缘黄土处于破坏后区状态,并产生不平衡剪应力。该不平衡剪应力驱动滑体向前移动,直至滑面只有一点处于临界状态,随即整个滑坡发生破坏,并伴随着滑体解体,产生泥流。这种破坏过程可以概括为：滑坡先产生剪破坏,紧接着后缘产生拉剪破坏,当破坏后区产生的驱动剪应力大于滑体的摩阻力,会推动滑坡向前移动,直至滑坡发生完全破坏。以理论和试验论证了这种破坏机制的正确性,并验证了一种新剪应力本构模型的合理性。     

某滑坡的力学机理分析与综合整治研究

深入分析了某滑坡的形态特征、结构特征及其力学机理,提出了一种新的选取滑坡抗剪强度参数的综合方法,并根据滑坡力学机理和各种整治措施的适用条件,经多方案的优化比选,提出了一种既经济又安全的整治方案。     

Geotechnical characterization of a landslide in a Blue Clay slope

This paper describes the results of an experimental, as well as theoretical, analysis of a landslide in a clay slope at the margin of a small town of Southern Italy, whose reactivation of 1998 caused severe damages to some structures. To protect the upslope urban area, an anchored diaphragm wall and a drainage system were constructed in 2001. In the meantime, in order to understand the processes which caused the reactivation, a Department of the Basilicata Administrative Region provided financial support to a geotechnical investigation. Laboratory tests on undisturbed and reconstituted specimens, in situ pore pressure and deep displacement measurements were carried out. Both experimental and theoretical in situ water content (and porosity) profiles were determined. Theoretical analyses of pore pressure distribution and stability analyses were carried out. The influence of the drainage system on the slope safety factor was evaluated. Experimental and theoretical data suggest that a first time process occurred in the lower part of the landslide system. The upper part moved on pre-existing surfaces on which an average shear strength close to the residual strength was available. Noticeable water content increase was found around some of these surfaces. Erosion at the toe of the landslide was the probable cause of reactivation. The analysis of the drain system effectiveness suggests that drainage has not significantly influenced pore pressures on the considered slip surfaces yet, mainly because of the very low permeability of the clay.     

Implementing landslide path dependency in landslide susceptibility modelling

Landslide susceptibility modelling—a crucial step towards the assessment of landslide hazard and risk—has hitherto not included the local, transient effects of previous landslides on susceptibility. In this contribution, we implement such transient effects, which we term “landslide path dependency”, for the first time. Two landslide path dependency variables are used to characterise transient effects: a variable reflecting how likely it is that an earlier landslide will have a follow-up landslide and a variable reflecting the decay of transient effects over time. These two landslide path dependency variables are considered in addition to a large set of conditioning attributes conventionally used in landslide susceptibility. Three logistic regression models were trained and tested fitted to landslide occurrence data from a multi-temporal landslide inventory: (1) a model with only conventional variables, (2) a model with conventional plus landslide path dependency variables, and (3) a model with only landslide path dependency variables. We compare the model performances, differences in the number, coefficient and significance of the selected variables, and the differences in the resulting susceptibility maps. Although the landslide path dependency variables are highly significant and have impacts on the importance of other variables, the performance of the models and the susceptibility maps do not substantially differ between conventional and conventional plus path dependent models. The path dependent landslide susceptibility model, with only two explanatory variables, has lower model performance, and differently patterned susceptibility map than the two other models. A simple landslide susceptibility model using only DEM-derived variables and landslide path dependency variables performs better than the path dependent landslide susceptibility model, and almost as well as the model with conventional plus landslide path dependency variables—while avoiding the need for hard-to-measure variables such as land use or lithology. Although the predictive power of landslide path dependency variables is lower than those of the most important conventional variables, our findings provide a clear incentive to further explore landslide path dependency effects and their potential role in landslide susceptibility modelling.     

Assessing landslide exposure in areas with limited landslide information

Landslide risk assessment is often a difficult task due to the lack of temporal data on landslides and triggering events (frequency), run-out distance, landslide magnitude and vulnerability. The probability of occurrence of landslides is often very difficult to predict, as well as the expected magnitude of events, due to the limited data availability on past landslide activity. In this paper, a qualitative procedure for assessing the exposure of elements at risk is presented for an area of the Apulia region (Italy) where no temporal information on landslide occurrence is available. Given these limitations in data availability, it was not possible to produce a reliable landslide hazard map and, consequently, a risk map. The qualitative analysis was carried out using the spatial multi-criteria evaluation method in a global information system. A landslide susceptibility composite index map and four asset index maps (physical, social, economic and environmental) were generated separately through a hierarchical procedure of standardising and weighting. The four asset index maps were combined in order to obtain a qualitative weighted assets map, which, combined with the landslide susceptibility composite index map, has provided the final qualitative landslide exposure map. The resulting map represents the spatial distribution of the exposure level in the study area; this information could be used in a preliminary stage of regional planning. In order to demonstrate how such an exposure map could be used in a basic risk assessment, a quantification of the economic losses at municipal level was carried out, and the temporal probability of landslides was estimated, on the basis of the expert knowledge. Although the proposed methodology for the exposure assessment did not consider the landslide run-out and vulnerability quantification, the results obtained allow to rank the municipalities in terms of increasing exposure and risk level and, consequently, to identify the priorities for designing appropriate landslide risk mitigation plans.     

Stability analysis of a large landslide in hydropower engineering

This paper is devoted to stability analysis of the Zheng-Gang landslide in the Gu-Shui hydropower station in China. Based on the geological field investigations, the formation processes, the deformation mechanism related to rainfalls and the instability mode are first analyzed. Large scale direct shear tests on soils in the slip zone are performed in order to characterize influences of the content of particle and water on natural shear strength. Due to the difficulty to consider the lateral constrain and curvature effects of the bottom sliding surface, different three-dimensional models are established using the limit equilibrium method and the large strain Lagrange finite difference method. The results of stability analysis are in good agreement with the field observations. It is shown that the natural landslide is in a limit state and the creep deformation along the slipping surface is the main mechanism of landslide instability under in situ conditions.     

滑坡变形对输气管道安全的影响分析

在对某输气管道线上一个正在活动滑坡变形和管道应变系统监测的基础上,分析了滑坡活动特征及其对管道安全的影响。滑坡监测采用地表位移监测,从而判断滑坡边界、掌握滑坡滑动状态对管道的影响;管道监测采用弦式应变计测其应变,利用强度理论评判管道的安全性。利用监测数据分析管道的轴向稳定性。监测结果表明,在该滑坡区域范围内管道尚属安全,但滑坡仍处于滑动阶段,对管道安全存在隐患。     

Displacement evolution of a creeping landslide stabilized with piles

Natural Hazards - In order to explore the displacement evolution of a creeping landslide stabilized with piles, an analytical model is proposed in this paper. Mechanical behaviors of the sliding...     

Back analysis of a large landslide in a flysch rock mass

Flysch is a sedimentary rock consisting of a rhythmic alternation of hard (limestone, sandstone, siltstone) and weak (marl, mudstone, claystone) layers. Because of the presence of layers with different physical properties, the mechanical characterization of heterogeneous rock masses such as flysch is a real challenge. Different methods have been proposed in the literature to characterize flysch, combining empirical classification indexes with laboratory tests. Most of these methods, however, were specifically designed for tunneling and underground excavations, and their applicability to slope stability problems is not yet fully investigated. In this study, we analyze a large landslide in a cretaceous flysch rock in order to compare the mobilized strength at failure with those predicted by the modified GSI method (Marinos and Hoek, 2001). The landslide occurred in the Savena River basin (Northern Apennines of Italy) on April 6, 2013, with a volume of about 3 million m³. Soon after the failure, geological, geotechnical, and geophysical investigations were carried out to detect the failure mechanism and define the landslide geometry. Back analyses of the failed slope were performed using both limit equilibrium and finite difference methods to estimate the in situ strength of the flysch. The results show that the mobilized rock mass cohesion is very low (c ^'?≈?20?÷?40 kPa) and that the modified GSI method can predict the in situ strength only assuming a disturbance factor D = 1. Moreover, the analysis shows that the linearization criteria proposed in literature to compute the equivalent Mohr-Coulomb parameters remarkably overestimate the rock mass strength.     

Reliability analysis of a large-scale landslide using SOED-based RSM

A design matrix in response surface method (RSM) that satisfies the orthogonality is very useful because the mean square error can be minimized, so that the response surface is more precise. But the orthogonality of a second-order design matrix in conventional RSM cannot be satisfied. In this paper, a second-order orthogonal experimental design (SOED)-based RSM is proposed by considering the orthogonality of high-order design matrix. The SOED is constructed by changing the length of star points, and the main characteristic of SOED is that the design matrix is diagonal. When the high-order terms are considered in the SOED-based RSM, a globe optimal solution can be found. As the regression equation is determined, the reliability index can be analyzed by the normalized distance between the mean value of the performance function and the critical limit state of the safety factor. A practical large-scale landslide with two slip surfaces is taken to verify the applicability and precision of the proposed method in detail. It is found that the SOED-based response surface is more rigorous than the conventional RSM.     

Use of LIDAR in landslide investigations: a review

This paper presents a short history of the appraisal of laser scanner technologies in geosciences used for imaging relief by high-resolution digital elevation models (HRDEMs) or 3D models. A general overview of light detection and ranging (LIDAR) techniques applied to landslides is given, followed by a review of different applications of LIDAR for landslide, rockfall and debris-flow. These applications are classified as: (1) Detection and characterization of mass movements; (2) Hazard assessment and susceptibility mapping; (3) Modelling; (4) Monitoring. This review emphasizes how LIDAR-derived HRDEMs can be used to investigate any type of landslides. It is clear that such HRDEMs are not yet a common tool for landslides investigations, but this technique has opened new domains of applications that still have to be developed.     

Evidence of a hidden landslide slip surface beneath a mountain hamlet

Earthquake-triggered landslides are some of the most destructive natural disasters. Although remote detection of landslides is economic and efficient, it may miss the more subtle signs of hidden landslides. The Kizawa Tunnel and facilities in its vicinity were severely damaged in the 2004 mid-Niigata Prefecture earthquake. After investigation of the most prominent cracks, the damage was attributed to the slip along a hidden weakness plane. Evidence supporting this argument is summarized in this paper. However, the extent of the shear plane is not limited to the interior of the northern part of the tunnel. The dislocation observed in the two wells to the south of the Kizawa Tunnel together with other findings from previous studies indicates that Kizawa hamlet lies on the southern extension of the same shear plane. Taking account of the presence of flat sedimentary structures, the shear plane may extend in all directions. The authors also surveyed other signs of damage along the perimeter where the shear plane intersects the ground surface. The geological and geomorphological features of the hidden landslide are discussed. Reactivation of interlayer sliding is a threat to the local residents, and thus more attention should be paid to monitoring the movement of the slope to avoid devastating damages.     

Seismically induced landslide displacements: a predictive model

Newmark's model for predicting earthquake-induced landslide displacements provides a simple way to predict the coseismic displacements affecting a sliding mass subject to earthquake loading. In this model, seismic slope stability is measured in terms of critical acceleration, which depends on the mechanical soil properties, pore-pressure distribution, and slope geometry. The triggering seismic forces are investigated in terms of energy radiation from the source, propagation, and site effects, based on 190 accelerometric recordings from 17 Italian earthquakes with magnitudes between 4.5 and 6.8. The method is based on the calibration of relations having the general form of an attenuation law that relates the energy of the seismic forces to the dynamic shear resistances of the sliding mass to propagate the expected landslide displacements as an inverse function of the distance from the fault rupture; the amount of displacement computed through these relations provides a criterion to predict the occurrence of slope failures. Finally, maps showing, in a deterministic and a probabilistic way, the potential of seismically induced landslide displacements are displayed as a tool to provide seismic landslide scenarios and earthquake-induced landslide hazard maps, respectively.     

The mechanism of a railway landslide caused by rainfall

This paper presents the study of a landslide induced by rainfall above a railway line in terms of site investigations, laboratory tests, finite element, and limit equilibrium analyses. The purpose of the study is to identify the cause and failure mechanism so as to prevent the recurrence of such failure. The slope concerned was composed of 3∼4 m thick fissured clay overlying highly weathered mica marble interbedded with quartz schist. The slope was cut into two steps and was protected by a masonry revetment and a thin masonry retaining wall at the toe. The region concerned suffered a whole month’s light drizzle in September, after which a rainfall of an intensity of 80 mm (in 48 h) occurred 5 days prior to the failure that happened on October 5, 2004. The rainfall infiltration and a failed drainage system behind the retaining wall resulted in high saturation of the clay and finally led to an undrained failure. The short-term slope stability using total stress parameters was examined by the finite element and limit equilibrium analyses. The factors of safety of the slope obtained by the finite element and limit equilibrium analysis were 0.935 and 0.854, which are in agreement with the occurrence of failure. Since the slide took place through the interface of the soil and rock, the exposure of rock has significant effect on the stability.     

蠕动型滑坡滑带土蠕变特性研究

蠕动型滑坡表现为长期缓慢的变形响应,其演化过程和稳定性受到滑坡滑带土蠕变性质的控制。选取三峡库区典型蠕动型滑坡马家沟滑坡为研究对象,针对该滑体滑带土原状试样开展大尺寸三轴蠕变试验,研究滑带土试样在不同围压和应力水平下的蠕变规律,并进一步采用等时曲线法确定滑带土长期强度与常规强度的差异。研究结果表明,马家沟滑坡滑带土具有典型的稳定蠕变材料特性,蠕变阶段可分为衰减蠕变和稳定蠕变2个变形过程,其变形趋势与滑坡宏观变形演化具有较好的一致性;滑带土绝对蠕变量和稳定蠕变阶段的变形速率均与轴向应力值呈正相关,而衰减蠕变阶段的持续时长随着剪应力水平增加基本呈线性增加。滑带土长期强度参数与常规强度参数比较,其长期黏聚力c值和长期内摩擦角?值分别下降24.8%和22.4%。