The genetic mechanism of a translational landslide

Translational landslides are common in China, particularly in the interbedded mudstone sandstone sequence of the Three Gorges reservoir area and the Sichuan basin. The paper discusses the genetic mechanism and limit equilibrium criterion for single and multi-translational landslides based on physical model tests and numerical analysis. It focuses particularly on the generation of hydrostatic pressure and uplift pressure under intense rainfall conditions and the corresponding deformation and failure processes. A model was constructed based on the actual conditions at the 17 million m³ Fengdian Kualiangdzi landslide and the 25 million m³ Tiantai village landslide. It revealed a clear relationship between the critical water head value and the dip angle of the sliding plane.      

Analysis of landslide stability under seismic action and subsequent rainfall: a case study on the Ganjiazhai giant landslide along the Zhaotong-Qiaojia road during the 2014 Ludian earthquake,Yunnan, China

In a strong earthquake, not only a large number of coseismic landslides are triggered, but relaxation and cracks in the rocks and soils are induced, which make these rocks and soils vulnerable to instability during subsequent rainfall; thus, strong earthquakes always have long-term effects on landslides. The geo-hazards along the Zhaotong-Qiaojia road in the 2014 Ludian earthquake (Ms 6.5) of Yunnan Province, China, were investigated, and the Ganjiazhai giant landslide was chosen as a case study. First, using the limit equilibrium analysis and Newmark method, the critical seismic intensity of the landslide before the earthquake was evaluated. Secondly, the dynamic failure process of the landslide under the measured ground motion was simulated with the discontinuous deformation analysis method. Lastly, based on stress–seepage coupling analysis and precipitation data from Ludian meteorological station, the stability of the landslide during subsequent rainfall after the earthquake was predicted. The results show that the critical seismic intensity was within degrees VIII–IX, which is consistent with the results of the earthquake damage investigation. The dynamic failure process can be divided into four stages, and four scarps formed; the potential sliding zones during the subsequent rainfall were at the first scarp and the fourth scarp, and their critical rainfall amounts were 35–40 mm and 55–60 mm, respectively. In this paper, failure process simulation and stability prediction of the landslide before, during, and after the strong earthquake are presented, which provide analysis methods for the dynamic stability of landslides in the meizoseismal area.

     

Spatial distribution and failure mechanism of water-induced landslides in the reservoir areas of Southwest China

Water-induced landslides in hydropower reservoirs pose a great threat to both project operation and human life. This paper examines three large reservoirs in Sichuan Province, China. Field surveys, site monitoring data analyses and numerical simulations are used to analyze the spatial distribution and failure mechanisms of water-induced landslides in reservoir areas. First, the general rules of landslide development in the reservoir area are summarized. The first rule is that most of the landslides have rear edge elevations of 100–500 m above the normal water level of the reservoir, with volumes in the range of 10⁶–10⁷ m³. When the volume exceeds a certain amount, the number of sites at which the landscape can withstand landslides is greatly reduced. Landslide hazards mainly occur in the middle section of the reservoir and less in the annex of the dam site and the latter half of the reservoir area. The second rule is that sedimentary rocks such as sandstone are more prone to landslide hazards than other lithologies. Then, the failure mechanism of changes in the water level that reduces the stability of the slope composed of different geomaterials is analyzed by a proposed slope stability framework that considers displacement and is discussed with the monitoring results. Permeability is an essential parameter for understanding the diametrically opposed deformation behavior of landslides experiencing filling-drawdown cycles during operation. This study seeks to provide inspiration to subsequent researchers, as well as guidance to technicians, on landslide prevention and control in reservoir areas.     

A coupled slope cutting—a prolonged rainfall-induced loess landslide: a 17 October 2011 case study

Continuous and heavy precipitation in the early September 2011 triggered several landslides in Xi’ an, Shaanxi province, China. A particularly relevant example is the Bailu tableland landslide occurrence on 17 September 17 2011, which was responsible for 32 casualties. This was selected as a case study for investigating the trigger factors, formation process, and hazard characteristics of the landslides of this type. The results showed that: (1) The Bailu landslide possessed a relative height = 90 m and width = 170 m, respectively, an average initiation thickness was 10 m, a sliding direction and distance of 55° and 150 m, respectively, a total volume of 15 × 10⁴ m³, and an average deposit thickness of 12 m; (2)The main trigger factors were excessive slope cutting with a heavy and long duration of rainfall; (3) The landslide was a typical example of its type, based on the trigger factors since the formation process of the landslide is generally as follows: cutting leads to gravitational and stress field redistribution, initiating the appearance of cracks, which then enlarge after the continuous infiltration of rainwater. This results in the formation of additional cracks, and finally, slope failure; a nd (4) Based on our analyses of this landslide and previous events, we proposed equations to determine the critical precipitation threshold and the potential risk distance. This study provided an important reference for understanding and studying the mechanisms of this type of landslide, as well as guidelines for future disaster prevention and mitigation in this region.     

Landslide dams triggered by the Wenchuan Earthquake,Sichuan Province,south west China

At 14:28 (Beijing time) on 12 May 2008, the catastrophic Ms 8.0 Wenchuan earthquake occurred just west of the Sichuan basin, China, causing severe damage and numerous casualties. It also triggered a large number of landslides, rock avalanches, debris flows etc. Some of the landslides formed natural dams in the rivers, with the potential secondary hazard of subsequent flooding. Through the interpretation of a series of aerial photographs and satellite images, 256 landslide dams were identified, although because of limited access, relatively detailed data were available for only 32. The paper presents statistical analyzes of the distribution, classification, characteristics, and hazard evaluation of these 32 dams. A case study of the 2.04 × 10⁷ m³ Tangjiashan landslide dam and the emergency mitigation measures undertaken is discussed.     

Volcanic mountain area disaster caused by the Iwate–Miyagi Nairiku Earthquake of 2008, Japan

We conducted an investigation of the geotechnical damage caused by an earthquake that struck on June 14, 2008. The earthquake was of magnitude 7.2 and hit a volcanic mountain area in Northern Japan. During the earthquake, the largest strong motion ever, over 4G, was recorded at the ground surface in the source region. As a result of the earthquake, a landslide of 1.5 million m³ was generated near the top of the mountain and became a mud flow, traveling about 10 km downstream. The geomorphic characteristics of the mud flow are reported in this paper. Another huge landslide was generated upstream near the Aratosawa Dam. It was about 1 km in length, about 700 m in width and had a sliding mass volume of about 67 million m³, which slipped about 320 m. The geological features, the time series of the slide and the cause of the slide are also discussed. In addition, more than 50 landslide dams, formed due to the collapsed soil and rock, appeared after the earthquake. In this paper, the geotechnical properties of all the damage are introduced.     

The Aso-Bridge coseismic landslide: a numerical investigation of failure and runout behavior using finite and discrete element methods

The complex coseismic process of the Aso-Bridge landslide during the main shock of the 2016 Kumamoto Earthquake was investigated. Finite element analysis and discrete element analysis considering vertical seismic accelerations (VSA) were conducted to explore the salient features of the prefailure mechanism and postfailure kinematic process of the coseismic landslide associated with the initiation time and kinematic runout behavior, respectively. Two seismic input conditions, one involving only horizontal seismic accelerations (HSA), and the other accounting for both HSA and VSA, were used to assess the influence of VSA from the prefailure to postfailure regimes. First, satisfactory agreement between the study and the published results in terms of landslide initiation time was obtained. As revealed by the rapid change of source displacement (RCSD), VSA did not alter landslide initiation time; however, it significantly increased the RCSD approximately 2-fold, which provided a clear initiation time. At landslide initiation, the estimated average velocities in a vertical direction increased approximately 16-fold (from −0.011 to −0.174 m/s) by accounting for VSA. Second, the results suggested that VSA had a trivial influence on runout behavior in the postfailure regime, given that such behavior was dominated by the collision and free fall during the sliding as well as the terrain features. With an average velocity of 21.34 m/s, the sliding source ultimately reached the riverbank within 21 s. The paper demonstrates that a combination of FEA and DEA can be used to investigate the coseismic process of the Aso-Bridge landslide and lead to satisfactory agreement with the event. Our comprehensive analysis provides insight into the role of VSA in earthquake-induced landslides.

     

Numerical and safety considerations about the Daguangbao landslide induced by the 2008 Wenchuan earthquake

The 2008 Wenchuan earthquake resulted in a large number of fatalities and caused significant economic losses.Thousands of landslides,many of which are very large,were triggered by the earthquake.A majority of catastrophic landslides were distributed along the central Longmenshan fault system,at the eastern margin of the Tibetan Plateau.Some of the landslides resulted in sudden damming of rivers causing flooding,which in turn induced secondary sliding disasters.Among the most significant landslides,the Daguangbao landslide was the largest in volume with the maximum thickness.For this,a numerical model of the Daguangbao landslide,using the material point method(MPM),was developed to simulate the interaction of the seismic loads imposed on the slope.The numerical results then are compared with the post-earthquake profile.As a consequence of the landslide,a nearly vertical head scarp with a maximum height of about 700 m was generated.This is considered as a high risk situation that requires constant monitoring and evaluation.Finally,we propose a methodology based on Bayesian networks(BNs) to manage the risk associated with the stability of the rockwall at the Daguangbao landslide site.     

Earthquake-triggered landslides by the 1718 Tongwei earthquake in Gansu Province,northwest China

The 1718 great Tongwei earthquake in northwest China caused more than 300 large-scale landslides near the epicenter resulting in more than 70,000 deaths. Although previous studies agree that the earthquake-induced landslides in the area are loess-landslides, which slid along ancient terrain surfaces, there is a dearth of evidence to unravel the actual failure mechanisms of these widely-documented events. To clarify their characteristics and mechanisms, the landslides in Pan’an Town, located in Gansu Province, China were rigorously investigated. The field surveys revealed that the landslides occurred in an area comprising loess deposits of several tens of meters underlain by a basal mudstone layer. It was also revealed that instability in the area is strongly influenced by a river valley with large erosion bank slopes, as well as steep mudstone slopes, which are well developed. The majority of the landslides triggered by the Tongwei earthquake were loess-mudstone composite landslides, with the sliding surface in the deep mudstone. Three huge landslides on the northern mountain located at the river bend of Pan’an Town with a total volume of about 6.06 × 10⁸ m³ are the main mass movements during the 1718 catastrophe. In addition, by taking the typical landslide named the Weijiawan landslide as a case study, the internal structure of the earthquake-triggered landslides and their stability were studied. The new findings not only aided the unraveling of the failure mechanisms but also provided insights and knowledge on early recognition of earthquake-triggered landslides in northwest China towns, especially in the surrounding valley, which shares similar geological conditions with landslides studied in this paper.     

三峡库区塔坪H2古滑坡台阶状复活变形的库水–降雨耦合作用机制

三峡水库蓄水以来,出现了大量大规模的老滑坡体复活现象。较多大型复活滑坡体的监测位移–时间曲线呈台阶状阶跃变化。此类滑坡的稳定状态识别难度较大,严重影响治理方案及治理时机的选择。以巫山曲尺塔坪H2滑坡为例,通过地质、位移监测及数值模拟方法,研究了此滑坡在实际降雨与库水涨落条件下渗流场、稳定性以及变形场演化规律。在汛期及库水位变动时期滑坡会发生变形,特别是库水位下降诱发滑坡前缘变形,并对后部坡体产生牵引作用。而降雨主要影响库水位变动带以上部分滑体的变形,并对前缘坡体产生推动作用。在周期性降雨和库水位涨落的循环作用下,滑坡体反复受到"推–拉"作用,导致滑坡的位移–时间曲线呈现台阶状阶跃特征。总体来说,库水位涨落是滑坡变形的主要因素,而降雨促进了滑坡变形进一步发展。     

“坡”、“场”因素对大型滑坡运动特征的影响

以滑坡的最大水平距离(Lmax)和视摩擦因数(Hmax/Lmax)为评价指标,探讨"坡"(滑坡体积(V)、滑坡高度(H)、滑坡坡度(α))和"场"(坡脚约束角(θ)、场地条件(X))因素对大型地震滑坡和降雨滑坡运动的影响特征。研究结果表明:在滑坡最大水平距离(Lmax)的影响上,滑坡高度(H)是降雨滑坡的主要因素,影响因素大小的顺序为H,α,θ和X。而对于体积为106～107 m3的地震滑坡,场地条件的影响比降雨滑坡大,其影响因素从大到小的顺序依次为H,X,α和θ。当地震滑坡体积大于107 m3时,滑坡坡度(α)则是Lmax的主要因素,影响因素从大到小的顺序依次为α,H,θ和X。显著性分析结果表明,滑坡高度(H)是大型降雨滑坡和体积为106～107 m3的地震滑坡的最大水平距离Lmax的显著性影响因素。在滑坡的视摩擦因数(Hmax/Lmax)的影响上,滑坡坡度(α)是地震滑坡的主要因素,影响因素从大到小的顺序依次为α,H,X和θ。而对于降雨滑坡,体积为106～107 m3时影响因素从大到小的顺序依次为α,H,θ和X;体积大于107 m3时,则影响因素从大到小的顺序依次为H,α,X和θ。显著性分析结果表明,H,α,X是体积大于107 m3的地震滑坡Hmax/Lmax的显著性影响因素。     

金沙江寨子村巨型古滑坡的工程地质特征及其发生机制

 通过现场调查,对金沙江寨子村巨型古滑坡的工程地质特征及形成机制进行较为深入的探讨。该滑坡后缘与前缘高差638 m,体积2.5×108 m3。主断壁外围发育有宽30～100 cm的冠裂缝,滑坡断壁为高5～30 m的石灰岩峭壁。滑源区地形起伏较大,内部发育有规模不一的冲沟,覆盖有发育植被的坡积物、倒石堆和直径1～6 m的巨石。滑坡主体为程海断裂带,断裂带背景地层主要为C2+3石灰岩,岩性为碎裂石灰岩和岩溶角砾岩。寨子村滑坡曾诱发严重的滑坡堵江事件,滑源区对面岸坡残留滑坡坝坝顶高出江面118 m,体积180×104 m3,由70%的粒径在30 cm以下的灰岩碎块和30%的粒径30 cm以上的灰岩、岩溶角砾岩块石组成。长200 km的程海断裂带是一条规模巨大的岩石圈断裂,长期活动导致带内及其两侧岩体质量降低。沿断裂带北西侧顺其走向流过的金沙江的底蚀作用使得右岸岸坡越来越陡,为其大规模失稳奠定基础。程海断裂带还是一条活动性断裂,其自身活动产生的地震是寨子村滑坡的诱发因素。     

罗山矿区滑坡灾害发生机制与监测预警技术研究

 随着矿山开采规模的日益扩大,罗山矿区已经形成滑坡体I,II,III,IV(体积约405.2×105 m3),严重制约着下方金、钼等多金属矿产资源的可持续安全开采。为能够对罗山矿区滑坡灾害进行超前预报,正确指导井下矿产资源的合理开采,首先,运用工程地质学、采矿学等理论分析罗山矿区滑坡体的形成机制,认为滑坡体松散–脆弱的地质结构和不合理采矿顺序是滑坡产生的主要原因,再加上降雨的催化作用加速滑坡的发生。其次,提出利用采矿治理滑坡的新思路,及时调整采矿顺序,从坡顶向坡脚开采,促使边坡向稳定方向发展。最后,以下滑力大于抗滑力是滑坡产生的充要条件作为滑坡体滑动的主要判据,应用滑坡远程监测预警系统在罗山矿区滑坡体上构建系统的滑坡体远程监测网。通过近10个月的现场试验,发现采用新的开采方案后,滑坡体朝着有利于边坡稳定的方向发展,从而证明采矿治理滑坡的科学性和可行性。     

岩门村滑坡高分辨率遥感调查与机制分析

 2007年7月7日,四川达县岩门村斜坡发生滑坡,造成直接经济损失约人民币1.5亿元。采用滑坡前后的高分辨率卫星影像及“数字滑坡”技术,获取滑坡地质环境及滑坡前后的道路、水塘、植被群位移及高程变化的定量信息,根据斜坡各部分变形特征,将其划分为主滑区、牵动滑区、强影响区及影响区4个部分,各自活动方式分别为快速推移+前缘砂土液化和面状流动,牵引(或后退)式滑移,受拉力发生拉张裂缝、错位和局部位移,以及受振动发生小规模的裂缝和错位。以DEM求得原地面以上的滑走及堆积方量分别为132.6×104和132.2×104 m3;结合钻孔资料求得滑面以上滑坡规模为1.97×106 m3。岩门村斜坡具备形成滑坡的岩性及坡体结构条件,但所临河谷狭窄,难以发育大型厚层滑坡,但有适宜的临空空间供局部浅层滑坡活动。长期强降雨是岩门村滑坡的主要触发因素。就斜坡整体而言,本次滑坡活动释放能量不充分,在连续降雨情况下局部可能再次发生浅层滑坡,但难以发生整体大规模滑移。     

一种新的节理本构模型及几种新的滑坡稳定系数计算方法

在对滑坡渐进变形分析的基础上,提出一种新的节理本构模型,推理出本构模型参数的决定方法;分析临界状态应力特征,提出临界状态应变方程,将提出的本构理论和现行莫尔–库仑临界状态准则实现无缝连接。分析现行滑坡稳定性系数计算方法的优缺点,相应地提出滑坡稳定性系数几种新的计算方法：基于渐进变形的临界状态稳定性系数计算方法、部分条块强度折减稳定性系数计算方法、综合下滑力–摩阻力稳定性系数计算方法、最大主下滑力滑坡稳定性系数计算方法,以及每一条块滑坡稳定性系数计算方法。对传统滑坡稳定性系数计算方法和本文提出的方法进行对比分析,进而提出综合下滑力–摩阻力稳定性系数以及最大主下滑力稳定性系数计算方法较能反应工程实践。最后,以实例对所提出的计算模型进行对比分析。     

Mapping the susceptibility of rainfall and earthquake triggered landslides along China–Nepal highways

The 2015 Gorkha earthquake (Mw?=?7.8) caused significant earthquake triggered landslides (ETL) in a landscape that is heavily intervened by rainfall triggered landslides (RTL). China’s Belt and Road Initiative plan to boost South-Asian regional trade and mobility through two key highway corridors, i.e. 1) Longmu–Rasuwa–Kathmandu (LRK) and 2) Nyalam–Tatopani–Kathmandu (NTK) route, that dissect the Himalayas through this geologically unstable region. To understand the spatial characteristics and susceptibility of these ETL and RTL, we delineate the landslides by means of time variant satellite imageries, assess their spatial distribution and model their susceptibilities along the highway slopes. We use a coupled frequency ratio (FR) – analytical hierarchy process (AHP) model by considering nine landslide determinants, e.g. geomorphic type (slope, aspect, curvature, elevation), hydrologic type (erosive potential of gullies, i.e. stream power index and distance to streams), normalized difference vegetation index, lithology and civil structure type (i.e. distance to roads). The results demonstrate that elevation and slope predominantly control both these landslide occurrences. The model predicts locations of ETL with higher accuracy than RTL. On comparison, NTK was safer with 133.5 km² of high RTL or ETL (or both) landslide susceptible areas, whereas LRK has 216.04 km². For mapping the extent of these landslides, we constricted it to the slope units of highways to reduce the computational effort, but this technique successfully achieved an acceptable threefold average model prediction rate of 82.75% in ETL and 77.9% in RTL. These landslide susceptibility maps and route comparisons would provide guidance towards further planning, monitoring, and implementing landslide risk mitigation measures for the governments.

     

Characterization of terrain surface and mechanisms of shallow landsliding in upper Kurokawa watershed,Mt Aso,western Japan

The paper describes the physical characteristics of the Mt Aso caldera (western Japan) where some 959 shallow landslides occurred between 1990 and 1998, denuding an area of 0.638 km². The variation in type and thickness of the recent pyroclastic deposits are described and linked to the spatial distribution of the landslides. The high monsoonal rainfall in July 1990 percolating into the recently deposited tephra overlying less permeable bedrock first saturated the soil mass and then effectively ‘floated’ the low density pyroclastic materials such that many slips occurred in the small, actively eroding, tributary valleys.      

Twin tunneling–induced deep-seated landslide in layered sedimentary rocks

Tunnel excavation in mountainous areas can sometimes reactivate or trigger landslides. The problem of tunneling-induced landslides may be influenced by not only the tunnel location and slope geological conditions but also construction deficiency without timely treatment. This paper presents a case study of Jimei landslide in Sichuan Province, China. This dormant landslide was largely induced by the excavation of a twin tunnel in the landslide body. Field investigation, slope movement monitoring, and numerical simulations show that the formation mechanism of the Jimei landslide triggered by tunneling can be summarized as follows: (1) The adverse geological conditions of stratified sliding mass consists of multilayer sliding surfaces and cracked sliding blocks. (2) The rock surrounding the tunnel underwent large and continuous deformation because of construction deficiency without timely treatment. (3) There was a reduction in the shear strength and increase in the bulk density of the sliding mass because of rainfall infiltration during the rainy season.

     

Dynamic discrete analysis of an earthquake-induced large-scale landslide

The Chiu-fen-erh-shan landslide, estimated to have a volume of 36 million cubic meters, was triggered by the M_w 7.6 Taiwan Chi-Chi earthquake of 1999. The debris covered an area of 1.95 km² and claimed 36 lives. During the sliding, the landslide mass disintegrated with its debris acquiring high speeds to reach over 1 km of travel distance. The main objectives of the study were to investigate if it was possible to numerically model the landslide progression, including slope disintegration, and to reproduce the post-failure configuration. Toward these goals, the study employed a discrete element method called discontinuous deformation analysis for the dynamic analysis. By incorporating the spacing and orientation information of the joints and bedding planes, the slope was modeled as an assemblage of discrete deformable blocks. Horizontal and vertical ground motions were simultaneously applied. The near-field digital strong records were affected by the large uplift of the hanging wall of the reverse thrust fault and corrections were made to address this issue. The study showed that the methodology adopted was able to capture essential characteristics of the landslide and gave a post-failure configuration resembling that observed in the field.     

牛圈沟高速远程滑坡超前冲击气浪机制分析

 为定量分析滑坡–碎屑流运动过程中所产生超前冲击气浪的强度及其演化规律,以牛圈沟高速远程滑坡为原型,采用计算流体力学软件,引入Voellmy准则定义运动阻力,在反演碎屑流运动全过程动力学行为特征的同时,对其前缘所产生超前冲击气浪的流场特征进行重点模拟,并论述和分析其形成的动力学机制。结果表明：(1) 牛圈沟高速远程滑坡的运动从启动到停止历时112 s,每一时刻其运动最大速度的空间位置出现在滑体内部靠近前缘的地方,其最大速度有2个峰值,分别是9 s时的52 m/s和49 s时的44 m/s;(2) 牛圈沟高速远程滑坡超前冲击气浪速度的最大值出现在9 s时,其值为45 m/s。压强最大值出现在滑体启动瞬间,为625 Pa,相当于11级暴风。滑体整体呈刚体运动时与前方空气接触面积最大,对其前方空气的挤压作用最为明显;(3) 随着滑体演化为碎屑流,前缘龙头高度逐渐降低(碎屑流厚度的变薄),其前方产生的超前气浪压强也随之降低,且其前方距碎屑流前缘越远,气浪压强越低;(4) 运动路径上的地形凸起、陡坎对超前冲击气浪的压强大小及其分布范围有较大影响,碎屑流前缘到达地形凸起点的坡脚时,会在凸起的迎风面产生梯度变化强烈的正压,而在凸起的背风面产生负压。当碎屑流由高向低飞下陡坎时,会强烈挤压前方空气,造成前方正压局部陡然增大。