Investigating the role of stratigraphy in large-area physically-based analysis of December 1999 Cervinara shallow landslides

The paper describes a large-area analysis of the triggering zones of shallow landslides on a case of unsaturated layered volcanic air-fall (pyroclastic) soil deposits in Cervinara site (18 km²), Southern Italy. The physically-based model TRIGRS (Transient Rainfall Infiltration-Based Grid Regional Slope-Stability) is used, which is used with either saturated or unsaturated conditions and implemented in a GIS platform. In addition to using the TRIGRS model to simulate some recent landslides, a new simplified approach is also tested to take into account the actual layered soil stratigraphy. The consistency check of the model and of the input data is performed with reference to slope stable conditions before rainfall. The performances of the models are evaluated through the ROC curves and two other quantitative indexes taken from the literature referring to the slope failures caused by December 1999 rainstorm. Notwithstanding the simplifications and limitations of the present work, both unsaturated conditions and layered stratigraphy are outlined as key factors for the slope stability of shallow deposits of unsaturated coarse-grained soils subjected to short heavy rainfall.     

基于模型试验的动水驱动型顺层岩质滑坡启滑机制初探

动水驱动型顺层岩质滑坡数量多、灾害频发、危害大, 是滑坡地质灾害领域的研究重点, 但目前对于滑坡启滑机制的认识仍不充分, 滑坡的准确预报还面临巨大挑战。鉴于此, 以含软弱夹层的中倾角顺层岩质滑坡为研究对象, 通过构建理想的单层滑带滑坡物理模型, 开展了一系列动水作用下的滑坡模型试验研究。结果表明, 动水作用下顺层岩质滑坡从开始变形至失稳滑动需经历初始变形、缓慢变形、加速变形和失稳破坏4个阶段, 而各个阶段的演化特征与滑面粗糙度和倾角密切相关。滑面倾角越大或粗糙度越小, 滑坡体从开始变形至失稳滑动所需的时间则越短; 相应地, 坡体加速变形阶段越不明显, 滑坡破坏的突发性越强。滑带内的渗流冲蚀作用会使滑带土中的骨料流失, 导致其抗剪强度降低, 进而引发坡体滑动。与此同时, 上覆坡体的压剪作用以及变形演化过程亦将反过来影响冲蚀强度。基于滑带土黏聚力随水力梯度和冲蚀时间的变化关系, 提出了渗流驱动下滑带土黏聚力演化模型, 可较好地描述滑带土黏聚力的退化过程。滑面粗糙度的存在不仅显著影响了滑带的冲蚀劣化规律, 还改变了滑带不同区域的破坏模式。此外, 通过考虑滑面粗糙度对滑带不同区域破坏模式的影响, 开展了动水多效应关联分析, 建立了滑坡地质体力学分析模型, 实现了动水作用下顺层岩质滑坡动态稳定性的有效评估。本研究成果可为实际动水驱动型顺层岩质滑坡的预测和防治提供理论参考。      

The intensity of slope and fluvial processes after a catastrophic windthrow event in small catchments in the Tatra Mountains

Strong wind events frequently result in creating large areas of windthrow, which causes abrupt environmental changes. Bare soil surfaces within pits and root plates potentially expose soil to erosion. Absence of forest may alter the dynamics of water circulation. In this study we attempt to answer the question of whether extensive windthrows influence the magnitude of geomorphic processes in 6 small second-to third-order catchments with area ranging from 0.09 km2 to 0.8 km2. Three of the catchments were significantly affected by a windthrow which occurred in December 2013 in the Polish part of the Tatra Mountains, and the other three catchments were mostly forested and served as control catchments. We mapped the pits created by the windthrow and the linear scars created by salvage logging operations in search of any signs of erosion within them. We also mapped all post-windthrow landslides created in the windthrow-affected catchments. The impact of the windthrow on the fluvial system was investigated by measuring a set of channel characteristics and determining bedload transport intensity using painted tracers in all the windthrow-affected and control catchments. Both pits and linear scars created by harvesting tend to become overgrown by vegetation in the first several years after the windthrow. The only signs of erosion were observed in 10% of the pits located on convergent slopes. During the period from the windthrow event in 2013 until 2019, 5 very small(total area 100 m2) shallow landslides were created. The mean distance of bedload transport was similar(t-test, p=0.05) in most of the windthrow-affected and control catchments. The mapping of channels revealed many cases of root plates fallen into a channel and pits created near a channel. A significant amount of woody debris delivered into the channels influenced the activity of fluvial processes by creating alternating zones of erosion and accumulation.     

福建东圳库区淹没及水土流失的3D-VRGIS构建与应用

本文应用VRGIS(Virtual Reality Geographical Information System)技术,建立水库工程水土流失三维可视化动态仿真模型,实现库区的空间信息可视化。以福建省东圳水库为研究对象,建立水土流失区域三维虚拟地理信息系统(3D-VRGIS),生成水土流失现状以及库区生态环境三维场景。并结合水土流失中水淹分析要素与三维空间的数据可视化技术,实现水土流失监测预报及其区域定位监控的可视化处理,为减少水土流失危害,提供可靠的信息资源。     

Slope Instability on Pyroclastic Deposits： Landslide Distribution and Risk Mapping in Zacapoaxtla, Sierra Norte De Puebla, Mexico

Introduction The impact produced by landsliding in diverse regions of the world has given rise to the development and implementation of different methods, techniques and tools to understand the mechanisms of movements involved, as well as to create maps o…     

Dynamic assessment of rainfall-induced shallow landslide hazard

The assessment of rainfall-induced shallow landslide hazards is a significant issue in the Three Gorges Reservoir area in China due to the rapid development of land in the past two decades. In this study, a probabilistic analysis method that combines TRIGRS and the point-estimate method for evaluating the hazards of shallow landslides have been proposed under the condition of rainfall over a large area. TRIGRS provides the transient infiltration model to analyze the pore water pressure during a rainfall. The point-estimate method is used to analyze the uncertainty of the soil parameters, which is performed in the geographic information system (GIS). In this paper, we use this method to evaluate the hazards of shallow landslides in Badong County, Three Gorges Reservoir, under two different types of rainfall intensity, and the results are compared with the field investigation. The results showed that the distribution of the hazard map is consistent with the observed landslides. To some extent, the distribution of the hazard map reflects the spatial and temporal distribution of the shallow landslide caused by rainfall.     

Geometrical and Geotechnical Characteristics of Landslides in Korea under Various Geological Conditions

The goal of this study is to determine the geometrical and geotechnical characteristics of landslides under various geological conditions using detailed field surveys, laboratory soil tests and precipitation records. Three study areas are selected to consider different rocks, including gneiss in Jangheung, granite in Sangju and sedimentary rocks in Pohang, South Korea. Many landslides have occurred in these three areas during the rainy season.Precipitation records indicate that landslides occurring in the gneiss area of Jangheung and granite area of Sangju may be influenced by the hourly rainfall intensity rather than cumulative rainfall.However, landslides occurring in the sedimentary rock area of Pohang may be influenced by hourly rainfall intensity and cumulative rainfall. To investigate the factors that influence these types of landslides, a detailed landslide survey was performed and a series of laboratory soil tests were conducted.According to the detailed field survey, most landslides occurred on the flanks of mountain slopes, and the slope inclination where they occurred mostly ranged from 26 to 30 degrees, regardless of the geological conditions. The landslide in the gneiss area of Jangheung is larger than the landslides in the granite area of Sangju and sedimentary rock area of Pohang.Particularly, the landslide in the sedimentary rock area is shorter and shallower than the landslides in the gneiss and granite areas. Thus, the shape and size of the landslide are clearly related to the geological conditions. According to the integrated soil property and landslide occurrence analyses results, the average dry unit weight of the soils from the landslide sites is smaller than that of the soils obtained from the nonlandslide site. The average coefficient of permeability of soils obtained from the landslide sites is greater than that of soils obtained from the non-landslide sites with the same geology. These results indicate that the soils from the landslide sites are more poorly graded or looser than the soils from the non-landslide sites.     

Zonal distribution of the erosion-landslide and soil micromorphological features in purple hilly region

In the purple hilly region, erosions and landslides are all serious, and it is of great scientific value and practical significance to study their formation mechanism and distribution features there.In this paper, soil micromorphological methods and techniques were used to study the erosion zonal distribution in the region. The results indicated: (1)According to erosion process, the spacial distribution zones of the erosions and landslides in the purple hilly region with different solums were divided into scouring erosion zone, transport-diffusion zone, rocks and soil turbulence zone and sediment-bury zone; (2) The soil micromorphologic taxonomic feature identifying different erosion-landslide zone were found by studying the soil micromorphology of erosive zone in purple hilly region; (3) As for the erosion-landslide formation in the region, besides the external factors, the internal factors were found more important and favorable for landslide formation through the studies on the micormorphologieal features of slide soil.     

Geomorphologic analysis and physico-dynamic characteristics of Zhatai-Gully debris flows in SW China

Zhatai gully is a typical debris flow channel in Butuo county of Sichuan province, southwestern China. The geomorphologic features are analyzed and the physical-dynamic characteristics are discussed on the basis of field investigation and laboratory tests. Geomorphologic analysis indicates that Zhatai-gully drainage in relation to debris flow can be divided into source area, transport area, and deposition area. The source area has a steep slope and has very limited vegetation cover, which favors runoff, allowing loose solid materials to be mobilized easily and rapidly. In the transport area, there are many small landslides, lateral lobes, and loose materials distributed on both banks. These landslides are active and constantly providing abundant source of soils for the debris flows. In the deposition area, three old debris-flow deposits of different ages can be observed. The dynamic calculation shows that within the recurrence intervals of 50 and 100 years, debris flow discharges are 155.77m³/s and 1y8.19m³/s and deposition volumes are 16.39 x 10⁴ m³ and 18.14 x 10⁴ m³, respectively. The depositional fan of an old debris flow in the outlet of the gully can be subdivided into six layers. There are three debris flow deposits on left and two on the right side of the gully. Grain-size tests of sediments from the soil, gulley bed deposits, and the fresh and old debris flow deposits showed that high amounts of clay and fine gravel were derived from the soil in the source area whereas much of the gravel fraction were sourced from the gully bed deposits. Comprehensive analysis indicates that Zhatai gully is viscous debris-flow gully with moderate to high frequency and moderate to large magnitude debris flows. The risk of a debris flow disaster in Zhatai-gully is moderate and poses a potential threat to the planned hydroelectric dam. Appropriate engineering measures are suggested in the construction and protection of the planned hydroelectric station.     

Submarine landslides on the north continental slope of the South China Sea

Recent and paleo-submarine landslides are widely distributed within strata in deep-water areas along continental slopes, uplifts, and carbonate platforms on the north continental margin of the South China Sea (SCS). In this paper, high-resolution 3D seismic data and multibeam data based on seismic sedimentology and geomorphology are employed to assist in identifying submarine landslides. In addition, deposition models are proposed that are based on specific geological structures and features, and which illustrate the local stress field over entire submarine landslides in deep-water areas of the SCS. The SCS is one of the largest fluvial sediment sinks in enclosed or semi-enclosed marginal seas worldwide. It therefore provides a set of preconditions for the formation of submarine landslides, including rapid sediment accumulation, formation of gas hydrates, and fluid overpressure. A new concept involving temporal and spatial analyses is tested to construct a relationship between submarine landslides and different time scale trigger mechanisms, and three mechanisms are discussed in the context of spatial scale and temporal frequency: evolution of slope gradient and overpressure, global environmental changes, and tectonic events. Submarine landslides that are triggered by tectonic events are the largest but occur less frequently, while submarine landslides triggered by the combination of slope gradient and over-pressure evolution are the smallest but most frequently occurring events. In summary, analysis shows that the formation of submarine landslides is a complex process involving the operation of different factors on various time scales.     

基于SBAS-InSAR的矿区采空区潜在滑坡综合识别方法

针对位于山区且受大量采空区影响的边坡,利用传统测量方法监测耗费人力、物力且光学遥感难以定量识别其是否为潜在滑坡的问题,本文提出一种融合研究区小基线集（SBAS-InSAR）地表监测数据、坡度及坡向的识别方法。通过SBAS-InSAR技术获得研究区地表雷达视线（LOS）方向形变速率,将其转化为垂直方向形变速率,并根据研究区DEM建立坡度及坡向分析图,根据不同山体的坡度、坡向找到易发生滑坡的区域,融入该区域垂直方向的时序形变速率,对其进行滑坡识别。实验表明：卡房镇周边受采空区的影响较大,多数区域垂直方向年形变速率大于10 mm/a;通过本文方法对研究区潜在滑坡进行识别,发现在研究区的21处历史滑坡点中,有16处被识别为潜在滑坡,5处未被识别但也位于发生形变的区域内,表明本文方法对潜在滑坡的识别精度高,具有可行性。该研究为识别采空附近的潜在滑坡提供了一种新的思路,可以有效识别采空区附近山体边坡是否处于潜在的、不明显的滑动状态,对滑坡灾害具有预警作用。     

基于修正Green-Ampt模型的降雨诱发区域浅层斜坡失稳灾害分析

由于具有类似的工程地质和水文地质条件, 在高度相关的降雨作用下, 同一个区域中的降雨诱发浅层斜坡失稳灾害常成群出现。在区域尺度预测浅层斜坡失稳灾害对滑坡灾害的防灾减灾工作具有重要的意义。为此, 提出了一种基于力学原理的降雨诱发浅层斜坡失稳灾害预测新模型RARIL。该模型采用修正Green-Ampt模型进行降雨入渗分析, 采用无限体边坡模型进行安全系数计算, 利用可靠度原理考虑区域斜坡稳定性分析中的参数不确定性。该模型具有可考虑降雨诱发浅层斜坡的失稳力学机理、可考虑区域内斜坡土体参数不确定性, 以及计算效率高、易于在GIS平台上实现等优点。案例分析表明, RARIL模型较为准确地预测了2010年8月12日11∶00至2010年8月14日9∶00期间强降雨在四川省汶川县映秀镇附近的303省道K0-K20段沿线区域引发的滑坡灾害, 研究结果证明RARIL模型在预测降雨诱发区域斜坡失稳灾害方面有很好的应用前景。      

贵州省不同地貌形态类型土壤侵蚀强度变化的定量分析

如何揭示不同地貌形态类型区土壤侵蚀强度变化,尤其是在生态环境比较脆弱的喀斯特区域,是地方生态保护战略实施亟需研究的关键问题之一。本文基于ALOS、ZY-3、GF-1、Landsat和GDEMV2遥感影像数据,以及2762条野外采样验证数据,参照国家在喀斯特与非喀斯特地区土壤侵蚀不同分类标准,实现10 m×10 m分辨率的贵州省2010年和2015年土壤侵蚀空间信息数据提取。进而结合贵州省地貌数据,通过构建贵州省土壤侵蚀的时空分析模型,实现对不同地貌形态类型,尤其是喀斯特区域和非喀斯特区域的土壤侵蚀强度的时空变化进行定量分析。结果显示：在2010—2015年,贵州省中—高海拔区域土壤侵蚀变化的动态度高于低海拔区域,土壤侵蚀强度总体呈下降趋势,下降总面积达6468.13 km2。喀斯特区域的土壤侵蚀变化广度高于非喀斯特区域的土壤侵蚀变化广度,而且变化趋势基本上是从高一级的侵蚀强度向低一级的侵蚀强度变化。高盆地、中山、高中山土壤侵蚀强度减弱趋势明显高于其他地貌类型的趋势,但高中山仍是喀斯特与非喀斯特区土壤侵蚀增强变化较为明显的区域。这说明自21世纪以来,在贵州喀斯特区域实施的生态修复工程和生态环境保护政策在土壤侵蚀防治过程中发挥了主导性作用,在今后贵州省进行土壤侵蚀防治的过程中,除了喀斯特区域的防治外,还需要同时注意非喀斯特区域的防治。     

基于GIS和USLE的东圳库区土壤侵蚀量预测研究

运用GIS、遥感技术与USLE模型相结合预测东圳库区流域土壤侵蚀量,利用GIS平台建立东圳库区基础地理数据库,以10×10m为栅格单元对库区进行离散化,在GIS空间分析功能支持下,结合USLE土壤侵蚀预测模型,根据合适的USLE因子算法生成栅格图层,通过图层运算,预测了东圳库区土壤侵蚀量,进而标识库区土壤侵蚀严重区域,为库区非点源污染控制及水土流失治理提供定量依据,并通过建立实用的泥沙输移比模型结合水文监测数据,对预测结果进行验证。根据USLE方程,采用改进后的SDR方程,预测的渡里流域年输沙量与流域实际监测得到的年输沙量仅相差14.08%,说明本文采用USLE方程模拟流域土壤侵蚀结果可信,可定量评价、拟定水土保持措施方案。     

Seismogenic fault and topography control on the spatial patterns of landslides triggered by the 2017 Jiuzhaigou earthquake

Jiuzhaigou National Park, located in northwest plateau of Sichuan Province, is a UNESCO World Heritage Site, and one of the most popular scenic areas in China. On August 8, 2017, a Mw 6.5 earthquake occurred 5 km to the west of a major scenic area, causing 25 deaths and injuring 525, and the Park was seriously affected. The objective of this study was to explore the controls of seismogenic fault and topographic factors on the spatial patterns of these landslides. Immediately after the main shock, field survey, remote-sensing investigations, and statistical and spatial analysis were undertaken. At least 2212 earthquake-triggered landslides were identified, covering a total area of 11.8 km~2. Thesewere mainly shallow landslides and rock falls. Results demonstrated that landslides exhibited a close spatial correlation with seismogenic faults. More than 85% of the landslides occurred at 2200 to 3700 m elevations. The largest quantity of landslides was recorded in places with local topographic reliefs ranging from 200 to 500 m. Slopes in the range of ~20°-50° are the most susceptible to failure. Landslides occurred mostly on slopes facing east-northeast(ENE), east(E), east-southeast(ESE), and southeast(SE), which were nearly vertical to the orientation of the seismogenic fault slip. The back-slope direction and thin ridge amplification effects were documented. These results provide insights on the control of the spatial pattern of earthquake-triggered landslides modified by the synergetic effect of seismogenic faults and topography.     

Hazards and landscape changes (degradations) on Hungarian karst mountains due to natural and human effects

In order to study the karstological processes within the karst ecological system,the geohazards and degradation of karst landscapes on the karst areas of the Bakony mountains(Hungary),we investigated the abiotic elements of the environment,soil and cover deposits,erosion soil decay;the changes in the quantity and quality of karst waters:contamination at swallow holes,contamination of karst springs;and the biogenic factors:surface vegetation coverage by the corine land cover method,plant-ecological examinations,qualification of surface waters with the help of biological water labeling.We recognized that the increasing human activities during the past few centuries have had significant impact on the investigated landscapes of karst areas because of their spatial sensitivity.In the scope of our research we concluded that the landscape changes due to natural and human effects can vary strongly on the different karst areas.These differences can arise from the climatic and geomorphologic situation,the coverlayer’s qualities,etc.,but primarily from the different utilization of the investigated karst areas(e.g.the intensity,characteristics and territorial extension of utilization).On the spot investigation we detected traces of new and fast geomorphological processes(gully formation,landslides,collapses,new sinkhole development) and landforms(sinkholes,gullies,swallow holes),which are clear evidences of the effect of climatic changes.     

Estimation of rainfall thresholds for shallow landslides in the Sierra Madre Oriental,northeastern Mexico

Landslides induced by prolonged rainfalls are frequent mass movements along the northeastern portion of the Sierra Madre Oriental in Mexico, causing significant damage to infrastructure. In this work, we have studied the connection between rainfall and landslides in the Santa Rosa Canyon, a catchment located in the northeastern Mexico. A landslide database triggered by major storms and hurricanes that have hit the region over the past 30 years was analyzed. A total of 92 rainfall events in the Santa Rosa Canyon were studied to determine the amount of precipitation needed to trigger shallow landslides. For each event the duration(D, in hours) and the cumulated rainfall event(E, in mm) were determined by using historical rainfall data from weather stations located near the study area. We have proposed an ED threshold for rainfall-induced landslides with durations 0.5 D 120 hours to address the conditions that trigger these events in the study area. On analyzing the obtained threshold, it has been established that almost 60 mm of a daily rainfall accumulation is required to trigger shallow landslides in the study area. This estimation is consistent with other calculations made for areas close to the Santa Rosa Canyon. Finally, we validated the predictive capability of the threshold with a different set of rainfall data that did not result in landslides performing a straightforward receiver operating characteristic analysis. A good approach was obtained, especially for rainfall events with daily measurements. Results could be used as input information in the design of a landslide early warning system for the northeastern Mexico, and replicated for other landslide prone areas in the region.     

Stability characteristics of shallow landslide triggered by rainfall

Rainfall induced shallow landslides are known to be extremely dangerous since the sliding mass can propagate quickly and travel far from the source. Although the sliding mechanism in sloping ground is simple to understand, the problem may be complicated by unsaturated transient water flow. The flow behavior of rainwater in unsaturated sloping ground and the consequent factor of safety must be clearly understood to assess slope stability under rainfall conditions. A series of laboratory experiments was conducted to examine the critical hydrological states so that assessment of slope stability under rainfall condition can be performed. Based on the test results, a unique relationship between critical hydrological states, rainfall intensity, and soil properties was formulated. Sequential stability analysis provided insights into the stability of slopes subjected to variations in soil properties, slope angles and rainfall intensities, and the consequent variation in the depth of the failure plane, vital in landslide risk assessment, was determined through this analysis.The variation of rainfall intensity was found to strongly affect the depth of the failure plane in cohesionless sloping ground. Furthermore, the influence of rainfall intensity on the depth of the failure plane may be alleviated by a small magnitude of cohesive strength. The results of this study will reinforce knowledge of landslide behavior and help to improve mitigation measures in susceptible areas.     

Managing Soil Erosion Potential by Integrating Digital Elevation Models with the Southern China's Revised Universal Soil Loss Equation——A Case Study for the West Lake Scenic Spots Area of Hangzhou,China

In China,many scenic and tourism areas are suffering from the urbanization that results from physical development of tourism projects,leading to the removal of the vegetative cover,the creation of areas impermeable to water,in-stream modifications,and other problems. In this paper,the risk of soil erosion and its ecological risks in the West Lake Scenic Spots (WLSS) area were quantitatively evaluated by integrating the revised universal soil loss equation (RUSLE) with a digital elevation model (DEM) and geographical information system (GIS) software. The standard RUSLE factors were modified to account for local climatic and topographic characteristics reflected in the DEM maps,and for the soil types and vegetation cover types. An interface was created between the Arcinfo software and RUSLE so that the level of soil erosion and its ecological risk in the WLSS area could be mapped immediately once the model factors were defined for the area. The results from an analysis using the Arcinfo-RUSLE interface showed that the risk value in 93 % of the expanding western part of the WLSS area was moderate or more severe and the soil erosion risk in this area was thus large compared with that in the rest of the area. This paper mainly aimed to increase the awareness of the soil erosion risk in urbanizing areas and suggest that the local governments should consider the probable ecological risk resulting from soil erosion when enlarging and developing tourism areas.     

Managing Soil Erosion Potential by Integrating Digital Elevation Models with the Southern China＇s Revised Universal Soil Loss Equation——A Case Study for the West Lake Scenic Spots Area of Hangzhou, China

In China, many scenic and tourism areas are suffering from the urbanization that results from physical development of tourism projects, leading to the removal of the vegetative cover, the creation of areas impermeable to water, in-stream modifications, and other problems. In this paper, the risk of soil erosion and its ecological risks in the West Lake Scenic Spots （WLSS） area were quantitatively evaluated by integrating the revised universal soil loss equation （RUSLE） with a digital elevation model （DEM） and geographical information system （GIS） software. The standard RUSLE factors were modified to account for local climatic and topographic characteristics reflected in the DEM maps, and for the soil types and vegetation cover types. An interface was created between the Areinfo software and RUSLE so that the level of soil erosion and its ecological risk in the WLSS area could be mapped immediately once the model factors were defined for the area. The results from an analysis using the Areinfo-RUSLE interface showed that the risk value in 93 % of the expanding western part of the WLSS area was moderate or more severe and the soil erosion risk in this area was thus large compared with that in the rest of the area. This paper mainly aimed to increase the awareness of the soil erosion risk in urbanizing areas and suggest that the local governments should consider the probable ecological risk resulting from soil erosion when enlarging and developing tourism areas.