Effects of river flow velocity on the formation of landslide dams

Natural dams are formed when landslides are triggered by heavy rainfall during extreme weather events in the mountainous areas of Taiwan.During landslide debris movement, two processes occur simultaneously: the movement of landslide debris from a slope onto the riverbed and the erosion of the debris under the action of high-velocity river flow. When the rate of landslide deposition in a river channel is higher than the rate of landslide debris erosion by the river flow, the landslide forms a natural dam by blocking the river channel. In this study, the effects of the rates of river flow erosion and landslide deposition(termed the erosive capacity and depositional capacity, respectively) on the formation of natural dams are quantified using a physics-based approach and are tested using a scaled physical model.We define a dimensionless velocity index vde as the ratio between the depositional capacity of landslide debris(vd) and the erosive capacity of water flow(ve).The experimental test results show that a landslidedam forms when landslide debris moves at high velocity into a river channel where the river-flow velocity is low, that is, the dimensionless velocity index vde 54. Landslide debris will not have sufficient depositional capacity to block stream flow when the dimensionless velocity index vde 47. The depositional capacity of a landslide can be determined from the slope angle and the friction of the sliding surface, while the erosive capacity of a dam can be determined using river flow velocity and rainfall conditions. The methodology described in this paper was applied to seven landslide dams that formed in Taiwan on 8 August 2009 during Typhoon Morakot,the Tangjiashan landslide dam case, and the YingxiuWolong highway K24 landslide case. The dimensionless velocity index presented in this paper can be used before a rainstorm event occurs to determine if the formation of a landslide dam is possible.     

Outburst risk of barrier lakes in Sichuan,China

34 barrier lakes induced by earthquake have been formed by wedged debris on the river channels after a massive earthquake happening on May 12 in Sichuan, China. Among them, the Tangjiashan Barrier Lake is the largest one. It faces very urgent risk of dam breaking when water level reaches the top and begins overflow in case of storm rainfalls and continually aftershocks, threatening already devastated cities and villages with about 1.5 million people downstream. The outburst of a similar barrier lake occurred in the Minjiang River in 1933, causing a catastrophic flood. Risk analysis indicates that not all barrier lakes are highly dangerous. Only those lakes with very high dams and water to be filled up in short period need to be dealt with immediately.     

滑坡堰塞坝堆积形态影响因素离散元分析

滑坡是形成堰塞坝的最主要原因,在地震、降雨、冰雪融水等作用下均可形成滑坡堰塞坝,而滑坡堰塞坝的堆积形态、范围等对评价堰塞坝的稳定性有着重要的影响。通过离散元方法(DEM),系统分析了三维条件下滑动距离、滑面出口宽度、滑面倾角、河床倾角、河谷形状对堰塞坝堆积形态的影响。研究结果表明:滑动距离和出口宽度对坝体高度影响最大;随出口宽度和坡面倾角的增加,坝长和坝宽分别呈线性增大和减小趋势;滑动距离可以有效控制滑体速度,进而影响堆积角大小;河床倾角主要影响坝长;对坝高、坝长、上下游绝对倾角正切值和堆积角正切值进行回归分析表明,数学模型契合程度高,说明其形态可以预测;引入2个参数λ和χ,对堰塞坝堆积特征进行了描述;河谷形状的影响主要体现在随着河谷底部宽度的增大,滑体爬高爬坡能力增强。研究成果对根据实际地形预测滑坡堰塞坝堆积形态进而评估坝体的安全性具有重要意义,可以为进一步开展堰塞湖溃决研究提供一定的参考。      

Rapid geometry analysis for earthquake-induced and rainfall-induced landslide dams in Taiwan

Stability analysis of the dam is important for disaster prevention and reduction. The dam＇s geometry plays an important role in understanding its stability. This study develops a rapid landslide dam geometry assessment method for both earthquake-induced and rainfall-induced landslide dams based on nine real cases collected in Chinese Taipei and 214 cases collected worldwide. For simplification purposes, a landslide dam is classified into triangular or trapezoidal. The rapid landslide dam geometry assessment method in this paper uses only satellite maps and the topographic maps to get landslide area, and then analyze the dam geometry. These maps are used to evaluate the area of the landslide and the slope of the river bed. Based on the evaluation information, the proposed method can calculate dam height, the length of the dam, and the angles of the dam in both upstream and downstream directions. These geometry parameters of a landslide dam provide important information for further dam stability analysis. The proposed methodology is applied to a real landslide dam case at Hsiaolin Village. The result shows that the proposed method can be used to assess the landslide dam geometry.     

高密度电阻率法在废弃矿山滑坡灾害勘察中的应用

高密度电阻率法是一种成熟的工程物探方法,广泛应用于地质灾害调查。废弃矿山在不良天气条件下容易产生滑坡地质灾害。对由废弃渣石、杂填土人工堆积形成的滑坡体进行勘察,研究高密度电阻率法在该环境下的勘察效果。通过对视电阻率反演断面图分析,推断滑动面深度、滑床起伏形态等滑坡体地质结构信息,为废弃矿山滑坡灾害治理设计提供依据。钻探验证表明,高密度电阻率法有效的推断出滑坡体滑动面深度、滑床起伏形态信息,可用于废弃矿山滑坡灾害勘察。     

The Séchilienne (France) Landslide:a Non-typical Progressive Failure Implying Major Risks

The National Road RN 91 has been threatened for about twenty-five years by a huge landslide, located 25 km south-east to the town of Grenoble (France). If several million cubic meters of rock fall down, the debris will dam the valley. Then the failure of the dam by overtopping and rapid erosion might result in a catastrophic flood and dramatic consequences for human life, environment and economy throughout the valley. The paper presents the hazard assessment based on geological and hydrological surveys, including small scale hydraulic tests, as well as the risk evaluation that has been performed. The risk management relies first upon a high level monitoring and an emergency plan; various mitigation strategies have been considered.     

Study on distribution rule of sliding pushing force and remnant resistant sliding force acting on anti-sliding pile

Anti-slide pile is one of the important methods to administer landslide geological disaster because of its advantages.It plays important role in administering landslide.It is a premise of reasonable economy and technological advance to know the distribution rule and feature of the force between anti-sliding pile and surrounding rock.To determine the sliding force and remnant resistant sliding force,according to need of study,this paper sets up the geological model and mechanics model in term of a typical landslide,and analyzes the effect rule of sliding body distortion,strength and gravity to the pushing force and remnant resistant sliding force by use of the numerical model.The distribution rule of pushing force and remnant resistant sliding force of the type of landslide is given.     

Study on distribution rule of sliding pushing force and remnant resistant sliding force acting on anti-sliding pile

Anti-slide pile is one of the important methods to administer landslide geological disaster because of its advantages. It plays important role in administering landslide. It is a premise of reasonable economy and technological advance to know the distribution rule and feature of the force between anti-sliding pile and surrounding rock. To determine the sliding force and remnant resistant sliding force, according to need of study, this paper sets up the geological model and mechanics model in term of a typical landslide, and analyzes the effect rule of sliding body distortion, strength and gravity to the pushing force and remnant resistant sliding force by use of the numerical model. The distribution rule of pushing force and remnant resistant sliding force of the type of landslide is given.     

汶川地震滑坡-碎屑流致灾距探讨

为了阐明地震滑坡的运动特性并对其进行致灾距的预测,基于遥感影像解译和野外调查数据,借助经验公式法,分析了汶川地震滑坡水平最大运移距离L与前后缘高差H之间的相关性,给出了经验公式;探讨了不同滑坡之间滑程的差异与异常。结果表明:若已知H,可用L=aH+b或L=aHb对总位移进行预测初探;将视摩擦系数H/L=0.45作为汶川地震高速远程型滑坡的上限较合适;滑坡体积、源区破裂面积与L呈正相关,与H/L呈负相关;地震滑坡易发生在山脊线平行于断裂带、垂直于地震波传播方向的山体两侧;崩塌型滑坡易发前后缘高差范围在10~100m之间,大型高速远程型滑坡易发前后缘高差大于200m;滑坡源区易发坡度分布在25°51°之间,滑床坡降变化范围为0~58°,高速远程型滑坡的滑床坡降主要在8°20°之间;分析认为滑程差异和异常是距离效应、能量传递与岩体挡板效应、滚动润滑与气垫效应、体积与破裂面积效应、地质因子、地形因子、颗粒级配与颗粒流效应等因素综合作用的结果,考虑上述因素有益于滑坡-碎屑流致灾距的预测分析。      

Failure mechanism and stability analysis of the Zhenggang landslide in Yunnan Province of China using 3D particle flow code simulation

Based on the principle of 3D particle flow code, a numerical landslide run-out model is presented to simulate the failure process of the Zhenggang landslide (in southwestern China) under the effect of water after a rainfall. The relationship between the micro-mechanical parameters and the macro-shear strength of the grain material is determined through numerical calibrations. Then the rainfall effect is considered in numerical simulations and rain-induced sliding processes are performed, which help us to discuss the mechanism of deformation and failure of this landslide together with field observations. It shows the Zhenggang landslide would most likely be activated in Zone I and would gain momentum in Zone II. In order to prevent the potential disaster, a tailing dam is advised to be designed about 175 m downstream from the current landslide boundary of Zone II. Verified by field observations, the presented landslide model can reflect the failure mechanism after rainfall. It can also provide a method to predict the potential disaster and draft disaster prevention measures.     

The formation of the Wulipo landslide and the resulting debris flow in Dujiangyan City,China

The Wulipo landslide, triggered by heavy rainfall on July 10, 2013, transformed into debris flow,resulted in the destruction of 12 houses, 44 deaths, and 117 missing. Our systematic investigation has led to the following results and to a new understanding about the formation and evolution process of this hazard. The fundamental factors of the formation of the landslide are a high-steep free surface at the front of the slide mass and the sandstone-mudstone mixed stratum structure of the slope. The inducing factor of the landslide is hydrostatic and hydrodynamic pressure change caused by heavy continuous rainfall. The geological mechanical model of the landslide can be summarized as "instability-translational slide-tension fracture-collapse" and the formation mechanism as "translational landslide induced by heavy rainfall". The total volume of the landslide is 124.6×104 m3, and 16.3% of the sliding mass was dropped down from the cliff and transformed into debris flow during the sliding process, which enlarged 46.7% of the original sliding deposit area. The final accumulation area is found to be 9.2×104 m2. The hazard is a typical example of a disaster chain involving landslide and its induced debris flow. The concealment and disaster chain effect is the main reason for the heavy damage. In future risk assessment, it is suggested to enhance the research onpotential landslide identification for weakly intercalated slopes. By considering the influence of the behaviors of landslide-induced debris flow, the disaster area could be determined more reasonably.     

基于地震信号反演滑坡动力学机制

以2003年千将坪滑坡事件为例，基于地震信号分析大型高速滑坡启动之后的滑体运动特性。通过国家地震台网采集因滑坡激发产生的地震信号，反演得到滑坡区域的受力-时间函数，再经由时频分析划分滑坡期间的子事件，进而推导滑体的运动参数并还原滑坡过程。结果显示，由地震信号反演所求得的滑床坡度、滑坡方向以及滑体位移等数值与现场勘踏所得数据相符；同时，通过对滑坡子事件的分析，可分辨出因对岸河堤阻挡而产生的部分滑体反倾过程，从而还原较完整的滑坡过程。     

Centrifugal model tests and numerical simulations for barrier dam break due to overtopping

The present study focuses on the breaching process and failure of barrier dams due to overtopping. In this work, a series of centrifugal model tests is presented to examine the failure mechanisms of landslide dams. Based on the experimental results, failure process and mechanism of barrier dam due to overtopping are analyzed and further verified by simulating the experimental overtopping failure process. The results indicate that the barrier dam will develop during the entire process of overtopping in the width direction, whereas the breach will cease to develop at an early stage in the depth direction because of the large particles that accumulate on the downstream slope. Moreover, headcut erosion can be clearly observed in the first two stages of overtopping, and coarsening on the downstream slope occurs in the last stage of overtopping. Thus, the bottom part of the barrier dam can survive after dam breaching and full dam failure becomes relatively rare for a barrier dam. Furthermore, the remaining breach would be smaller than that of a homogeneous cohesive dam under the same conditions.     

Size and spatial distribution of landslides induced by the 2015 Gorkha earthquake in the Bhote Koshi river watershed

The Mw 7.8 Gorkha earthquake in Nepal on April 25, 2015, produced thousands of landslides in the Himalayan mountain range. After the earthquake, two field investigations along Araniko Highway were conducted. Then, using remote sensing technology and geographic information system(GIS)technology, 1481 landslides were identified along the Bhote Koshi river. Correlations between the spatial distribution of landslides with slope gradient and lithology were analyzed. The power-law relationship of the size distribution of earthquake-induced landslides was examined in both the Higher Himalaya and Lesser Himalaya. Possible reasons for the variability of the power exponent were explored by examining differences in the geological situations of these areas. Multi-threshold cellular automata were introduced to model the complexity of system components. Most of the landslides occurred at slope gradients of 30°–40°, and the landslide density was positively correlated with slope gradient. Landslides in hard rock areas were more common than in soft rock areas. The cumulative number-area distribution of landslides induced by the Gorkha earthquake exhibited a negative power-law relationship, but the power exponents were different: 1.13 in the Higher Himalaya, 1.36 and Lesser Himalaya. Furthermore,the geological conditions were more complex and varied in the Lesser Himalaya than in the Higher Himalaya, and the cellular automata simulation results indicated that, as the complexity of system components increased, the power exponent increased.Therefore, the variability of the power exponent of landslide size distribution should ascribe to the complexity of geological situations in the Bhote Koshi river watershed.     

2015-04-25尼泊尔M8.1地震震害特征

2015-04-25尼泊尔M8.1级地震造成我国西藏日喀则地区10个县的房屋设施不同程度地破坏,最大影响烈度为IX度。灾区调查发现,土木和石木等简易结构房屋普遍破坏,砖混和框架结构房屋破坏较轻。受场地条件影响,沿雅鲁藏布江破坏比其他地区较普遍。极震区滑坡、崩塌等地震地质灾害造成的人员伤亡和财产损失比地震动直接造成的损失更大。     

香丽高速公路昌格洛滑坡-隧道工程病害三维数值分析

准确评价滑坡-隧道相互作用及稳定性, 采用合理的病害防治方法, 对保障公路顺利完工具有重要意义。以香丽高速公路昌格洛滑坡为例, 利用现场地质调查、钻探等方法查明了滑坡成因机制以及变形特性, 通过数值模拟研究了昌格洛滑坡在天然、降雨和开挖等工况下的空间应力应变特征以及稳定性变化, 研究了隧道与所穿越滑坡之间的相互作用, 据此提出了相应的病害防治方案。结果表明: 昌格洛滑坡在自然条件下处于欠稳定状态; 隧道开挖难以引起滑坡整体失稳, 但会诱发滑坡局部变形, 受滑坡体变形影响, 穿越滑体的隧道部分将产生拉伸-剪切变形; 降雨严重恶化滑坡稳定性, 导致滑坡失稳, 进而使穿越其中的隧道失效破坏。原选线方案面临风险巨大, 最优防治方案为线路东移绕避, 使隧道从滑面以下穿过。研究方法和成果可为香丽高速公路类似病害的防治提供有益借鉴。      

三峡库区马家屋场-后坪滑坡成因及稳定性分析

详细介绍了三峡库区马家屋场-后坪滑坡体的特征，收集了大量软弱结构面资料，研究了各软弱结构面的组合关系，运用优势面理论，合理解释了该滑坡体的成因。采用剩余推力法，对滑坡体在各种不同工况下的稳定性作了科学分析，并对滑坡体在三蛱水库蓄水以后的稳定性作了合理预测，结果表明，滑坡体在目前状态下基本稳定，三峡水库蓄水以后，将对滑坡体稳定性产生较大影响，极有可能导致滑坡体失稳。     

地震动触发滑坡体滑动的机理

论证并探讨了地震动触发滑坡体滑动的机理,认为地震时的坡体波动振荡在斜坡岩土体变形破坏过程中产生三种效应：累进破坏效应、启动效应和启程加速效应,并得出了一些既有理论研究意义,又有一定实际应用价值的论断。     

黄河大柳树坝址岩体破坏机制动力模拟试验分析

黄河黑山峡大柳树坝址区存在大范围的岩体松动破坏现象，其主要特征是岩体应力释放，结构面张开，密度显著下降。为进一步研究岩体松动的成因机制，在详细调查区域地质背景条件及区域地震动力作用基础之上，提出了地震动力作用与岩体松动现象的内在联系。通过动力模拟试验进一步证明大柳树坝址区存在的大深度、大范围岩体松动与历史上该地区发生的强烈地震具有密切关系。因此在目前的工程地质条件下，一旦发生较大强度的地震活动，坝址区所遭受的破坏程度会更大，对拟建的水利工程设施将产生严重威胁。     

Evidence of the formation of landslide-dammed lakes in the Zagros Mountains range,Iran

Alternation of high and low resistance sedimentary beds,active tectonics,large rivers,and slope erosion in valleys consequently resulted in landslide in dammed lakes within the Zagros range.This study presents the results in the analysis of geological and topographic data,satellite imageries,morphotectonics and hydrodynamics of drainage networks about the landslide dammed lakes.There are four landslides in central Zagros(Zagros FoldThrust Belt,ZFTB)which have formed five dammed lakes named,Seymareh,Jaidar,Shur,Shimbar,and Godar.According to the results,damming landslides occurred in the active-tectonic regions on the slopes of anticlines and in valleys with undercutting effects of rivers on their slopes consisting of alternations of loose and resistant beds.The studied landslide dams in narrow valleys are formed as a result of blocking river by sliding debris slopes and rock slides.This study also indicates the formation of Jaidar and Godar in one stage and the presence of Lake Terrace sequence in Seymareh,Shur and Shimbar lakes.The observed sequences of terrace formation in these lakes are caused by four Seymareh Landslides followed by the three-stage excavation of Shur andShimbar lakes.