Seismic landslide simulations in discontinuous deformation analysis

Discontinuous deformation analysis (DDA) is a numerical approach used to simulate the post-failure behavior of a blocky assembly. Three available algorithms incorporate seismic impacts into DDA simulations for earthquake-induced slope failure. The following methods are used: directly applying time-dependent accelerations to falling/sliding blocks (Method 1); adding time-dependent accelerations to base block (Method 2); and time-dependently constraining seismic displacements of the base block (Method 3). However, incorrect absolute movements of falling/sliding and base blocks were obtained using Method 1. Additionally, relative movements between falling/sliding blocks and the base block are opposite to those simulated by the other two algorithms—Methods 2 and 3. Since locating an earthquake-induced landslide before an earthquake is extremely difficult, the seismic movements of base rock are recorded. Method 1 applies recorded seismic data to sliding blocks in conflict with d’Alembert’s principle of mechanics. Additionally, in Method 2, when the computation time step must be longer than the time in seismic data, computational results reveal abnormal base block displacements due to the non-zero velocity recorded at the end time of seismic data in seismic DDA. In this study, a novel algorithm to diminish the velocity of the base rock in the seismic analysis is utilized to modify Method 2. Furthermore, this work confirms that DDA with the modified Methods 2 and 3 is a practical approach for earthquake-induced landslide simulations.     

考虑滑床摩擦弱化的大光包滑坡运动机制DDA数值模拟研究

2008年汶川发生M_S8.0级地震,此次地震触发了大约20万处滑坡,其中大光包滑坡是汶川地震触发的最大规模的滑坡,其复杂的高速远程运动机理引起了国内外学者的广泛关注。本文结合热分解及动态结晶将地震中断层间摩擦弱化机制(闪速加热导致热分解及粉末润滑)运用于大光包滑坡高速远程运动的模拟。本文通过修改非连续变形分析(DDA)程序中强度参数的输入方式,以基于速度变化的强度参数取代原DDA程序中的常数强度参数,进而实现了摩擦系数随接触两侧相对速度变化的动态调整。运用修改后的DDA对大光包滑坡的运动过程进行模拟。模拟结果表明滑床摩擦弱化是导致大光包滑坡高速远程运动特征的重要原因,修改后的DDA由于考虑了滑床摩擦弱化能够更加合理地模拟滑坡的高速远程运动特征,本文模拟的大光包滑坡在地震作用下失稳后,由于滑床摩擦弱化,更多的能量转化为动能,高速滑体掠过黄洞子沟后,爬上对面的平梁子,最终由于平梁子的“急刹车”作用,滑体停止运动。与修改前DDA相比,修改后的DDA对大光包滑坡运动过程和最终堆积形态的模拟结果与已有文献记载和野外调查结果相吻合。这也间接证明了大光包滑坡滑动过程中由于白云岩间摩擦闪速加热导致热分解及粉末润滑造成的摩擦系数降低,可能是造成大光包滑坡高速远程运动的重要原因。     

The mechanism of the 1941 Tsaoling landslide, Taiwan: insight from a 2D discrete element simulation

Tsaoling is located in Southwestern Taiwan, 10 km east of the frontal thrusts of the mountain belt. Five large historical landslide events were recorded from 1862 to 1999. No details of the earliest landslide event (1862) are available, thus this paper deals with the 1941 landslide event. Using the Particle Flow Code in two dimensions (PFC 2D) to simulate the mechanism of the Tsaoling landslide in 1941, this study shows that the landslide block developed cracks and slid down 0.2–1.8 m on the sliding plane. The cracks concentrated in certain zones, which corresponded to future landslide detachment planes. During the vibration simulation, the cracks spread from the shear plane to ground surface. Monitoring the variations of the displacements, velocity, and stress during vibration simulation showed that the peak velocity and stress in the transition zones occurred at 3 s. The displacement of the left part of the block exceeded 1.3 m, and the displacement of the right part was less than 1.3 m during vibration simulation. These results suggest that the left part of the block was pushed down by the right part, ultimately inducing a landslide during an earthquake.     

Evaluation of slope stability by finite element method using observed displacement of landslide

To monitor land deformation in detail, we ran a large-scale field test in which an artificial landslide was induced by the application of a load to a natural slope. The measured landslide displacement was reproduced numerically through the use of finite element model analysis with a two-dimensional elasto-viscoplastic model. The analysis suggested that the strength of the sliding surface decreased as the landslide mass moved. We propose a simple method for estimating safety factors. The method involves back-calculation of shear strength parameters through reproduction of observed landslide displacements and calculating the ratio of driving force to resisting force acting on the sliding surface as modeled by joint elements. This ratio, the “stability index”, shows the same trend as safety factors calculated by a two-dimensional limit equilibrium method and a shear strength reduction method that use back-calculated shear strength parameters estimated from the limit equilibrium state. The results indicate that the stability index may be applicable to the assessment of slope stability.     

金乐滑坡滑带土抗剪强度参数分析与确定

滑坡滑带土抗剪强度参数是滑坡稳定性分析和治理工程设计的最基本、最重要参数,它的大小及其变化直接影响到滑坡稳定性的计算,并由此得到不同的结果和涉及到治理措施的有效性。通过室内试验、滑带土现场原位大剪试验、反分析值及相似滑坡类比法综合确定三峡库区金乐滑坡滑带土的抗剪强度参数,指出该滑坡滑带土抗剪强度参数的确定和分析应采用多种方法,才可获得合理可行的结果。      

Applying disk-based discontinuous deformation analysis (DDA) to simulate Donghekou landslide triggered by the Wenchuan earthquake

In this paper, for the first time, disk-based discontinuous deformation analysis (DDA) is applied to simulate a real landslide triggered by an earthquake. For this purpose, the kinematic behaviour of the Donghekou landslide triggered by the Wenchuan earthquake is simulated and the results obtained using disk-based DDA are compared with actual data. The comparisons show that there is a good agreement between the results obtained using disk-based DDA and observed data. The simulation results provided an understanding of the failure behaviour and temporal evolution of the landslide. This study shows that disk-based DDA is a practical numerical tool that can be used to simulate the post-failure behaviour of landslides triggered by an earthquake.     

Experimental and numerical investigations of a catastrophic long-runout landslide in Zhenxiong,Yunnan, southwestern China

On 11 January 2013, a catastrophic landslide of ～0.2 million m³ due to a prolonged low-intensity rainfall occurred in Zhenxiong, Yunnan, southwestern China. This landslide destroyed the village of Zhaojiagou and killed 46 people in the distal part of its path. The displaced landslide material traveled a horizontal distance of ～800 m with a vertical drop of ～280 m and stopped at 1520 m a.s.l. To examine the possible mechanism and behavior of the landslide from initiation to runout, the shear behavior of soil samples collected from the sliding surface and runout path was examined by means of ring shear tests. The test results show that the shear strength of sample from the sliding surface is less affected by shear rate while the shear rate has a negative effect on the shear strength of runout path material. It is suggested that the source and runout path materials follow the frictional and Voellmy rheology, respectively. Post-failure behavior of the landslide was modeled by using a DAN-W model, and the numerical results show that the selected rheological relationships and parameters based on the results of ring shear tests may provide good performance in modeling the Zhenxiong landslide.     

库岸深层老滑坡间歇性复活的动力学机制研究

库岸深层老滑坡在季节性降雨和周期性库水位变动联合作用下往往表现出间歇性复活特征。在这一复活过程中,滑动期与间歇期交替出现,滑带土经历不同速率的剪切和不同时长的固结。从滑动期内残余强度的剪切速率效应、间歇期内峰值抗剪强度的恢复特征以及间歇期过渡到滑动期的孔隙水压力触发过程3个方面着手,建立了描述库岸深层老滑坡间歇性复活的动力学方程。塘角村1号滑坡滑带土试样的环剪试验结果显示：残余强度在较小速率范围内表现出负速率效应,而当剪切速率达到一定值后残余强度不再减小,且有微弱增长趋势;峰值强度在短时间内有较明显的恢复,但在较小位移后衰减至残余强度;孔隙水压力触发剪切破坏的发生滞后于所施加的水压力,这一滞后过程为孔隙水压力的扩散过程。基于试验成果,根据所建立的动力学方程,对库岸深层老滑坡间歇性复活的动力学机制进行了讨论,从而为此类滑坡的预测和防灾减灾提供有价值的参考。     

侵蚀作用诱发黄土滑坡的机制研究

侵蚀作用诱发的黄土滑坡是黄土高原区域内一种主要的滑坡类型,对其破坏机制开展深入研究具有重要实际意义。以陕西省耀州区的庵里滑坡为例,对该类黄土滑坡的发生机制进行分析和探讨,建立了滑坡发生前侵蚀作用的不同阶段边坡的有限元模型,计算了相应的应力场和位移场,在此基础上求得各模型沿最终滑面上的正应力、剪应力和抗剪强度分布,采用极限平衡法计算边坡整体稳定系数。结果表明,随着侵蚀作用的不断加深,沿滑动面上的剪应力增大,抗剪强度减小,整体稳定性降低至最终破坏。试验结果表明,小的应变在饱和黄土中会产生显著的超孔隙水压力,因此,基岩面上饱和滑带中的超孔隙水压力加剧了该类滑坡的发生。比较滑面上的剪应力和抗剪强度发现,自前滑坡破坏从坡脚开始,向后逐步扩展,表明该类滑坡具有牵引式破坏特点。     

基于滑带强度参数动态演化的滑坡稳定性研究

基于滑带应力状态分析和室内试验,提出了基于滑带强度参数动态演化的滑坡稳定性评价方法,并将应力状态作为评价滑面力学参数的主要指标,以合理地反映滑面强度状态对滑坡稳定性的影响。通过室内试验,获得了滑面强度参数与工程性状、力学参数之间的量化关系,在该基础上,通过数值计算,对滑面的力学参数和滑坡的稳定性进行三维计算。计算结果表明,利用提出的方法能较好地反映出滑带强度参数的空间分区特征。同时,对工况变动情况下滑带的强度参数进行量化取值,并对滑坡的稳定性进行动态计算,提出的计算方法更能体现出滑坡力学参数与稳定性的动态变化过程。     

Mechanism and failure process of Qianjiangping landslide in the Three Gorges Reservoir,China

The Qianjiangping landslide is a large planar rock slide which occurred in July 14, 2003 shortly after the water level reached 135 m in the Three Gorges Reservoir, China. The landslide destroyed 4 factories and 129 houses, took 24 lives, and made 1,200 people homeless. Field investigation shows that the contributing factors for the landslide are the geological structure of the slope, the previous surface of rupture, the water level rise, and continuous rainfall. In order to reveal the mechanism and failure process of the landslide, numerical simulation was conducted on Qianjiangping slope before sliding. Based on the characteristics and the engineering conditions of the landslide, the topography and the geological profiles of Qianjiangping slope before sliding is reconstructed. The seepage field of Qianjiangping slope before sliding was simulated with the Geostudio software. The results show that ground water table rises and bends to the slope during the rise of water level, and the slope surface becomes partially saturated within the period of continuous rainfall. Using the ground water table obtained above, the failure process of Qianjiangping slope is simulated with the Flac3D software. The results demonstrate that the shear strain increment, displacement, and shear failure area of the slope increased greatly after the water level rose and continuous rained, and the landslide was triggered by the combined effect both of water level rise and continuous rainfall. The development of shear strain increment, displacement, and shear failure area of the slope shows that the landslide was retrogressive in the lower part of the slope and progressive in the upper part of the slope.     

三峡库区万州安乐寺滑坡滑带特征

安乐寺滑坡是三峡库区典型的缓倾角红层基岩滑坡, 对其滑带特征进行详细的研究有助于揭示缓倾角红层基岩滑坡的形成机制.宏观地质特征显示, 安乐寺滑坡滑带是侏罗系红层中灰白色泥岩(软弱夹层) 经挤压滑动所形成的, 擦痕指示最后一次滑动方向为100°.通过X射线衍射分析和红外光谱分析表明, 安乐寺滑坡滑带主要矿物成分为蒙脱石、伊利石、长石、石英等; 其特点是蒙脱石含量高, 并且滑动面上的蒙脱石含量高于滑带的蒙脱石含量.经扫描电镜观察, 滑带土微观结构以片状结构与定向排列结构为主; 显微擦痕发育, 并指示滑带曾发生过多次滑动.对滑带土的物理力学性质进行实验研究可知: 滑带土为中等膨胀性粉质粘土, 其抗剪强度低; 且吸水膨胀后, 抗剪强度大大降低.滑带土的这些特殊性质, 为安乐寺滑坡的滑动提供了物质基础.      

The anatomy of an active slide: the Gascons rockslide,Québec,Canada

A railroad crosses the coastal Gascons rockslide, in Quebec, Canada. This study improves the understanding of the rockslide’s failure mechanism and post-failure behaviour responsible for the deformation in the railroad. The slide is an asymmetrical wedge failure of 410,000 m³, in rocks made up of centimetre-scale beds of nodular calcilutite alternating with sandstones and limestone. The post-failure stage of the rockslide is characterised by continuous movement of blocks with speeds ranging from 6 to 110 mm/year. The main water table is just below the sliding surface, but precipitation and snowmelt can raise it above the sliding surface in the upper part of the slide. We propose a model for the rockslide, its failure mechanism, geometry and hydrogeology to provide a baseline for interpreting the near-real-time data collected since 2009.     

Implementation of displacement-dependent Barton-Bandis rock joint model into discontinuous deformation analysis

Discontinuous deformation analysis (DDA) has been widely applied in analyzing various rock engineering problems. As the joint strength play a vital role in the stability of jointed rock mass, this paper makes an attempt to implement the Barton-Bandis rock joint model into the DDA code to replace the original Mohr-Coulomb joint model. The developed Barton-Bandis joint model which is characterized by displacement-dependent shear strength is verified by experimental direct shear tests. An example of a block sliding on an inclined plane is used to demonstrate the capacity of the DDA-BB model in predicting the dynamic motion behavior of sliding blocks.     

甘肃黑方台滑坡类型与活动特征研究

由于农业灌溉水的长期入渗软化作用,1984-2019年甘肃黑方台已频繁发生滑坡灾害约150次,沿黄土塬边形成长约10公里的滑坡密集发育带。滑坡类型以中、小型黄土层内滑坡为主,占90%以上;大、中型黄土-泥岩顺层滑坡次之。黄土层内滑坡速度快、滑程远,突发性、频发性、继发性强;黄土-泥岩顺层滑坡速度慢、滑程近、复活性强。高陡的台缘地形和强度低、水敏感性强的岩土体和岩层倾向坡外的地质结构是滑坡发生的基础,台塬区长期大量的农业灌溉是主要引发因素,大量水体入渗软化斜坡岩土体,使抗剪强度降低,并形成了约20多米厚的饱和软弱基座,导致斜坡失稳滑动,侧压力、季节性冻结滞水和溶滤作用等也有一定影响。黄土层内滑坡高速远程滑动的主要原因是：滑坡剪出口位置高,滑动势能大,释放条件好,剪出口下部有陡坡加速段和开阔、平缓的滑动空间,滑体底部饱和软弱黏性土持续产生超孔隙水压力、液化等低摩阻效应,是远程滑动的润滑剂。黄土-泥岩顺层滑坡的主滑面沿外倾15°左右的泥岩层面发育,且剪出口位于斜坡下部坡脚部位,能量释放条件差,决定了黄土-泥岩顺层滑坡的滑动速度较低、滑动距离较短,滑体易再次复活滑动。     

基于动态残余强度的不同含水率条件下滑坡稳定性研究

长时降雨会引起斜坡发生累进性破坏,在此过程中,滑带土将随含水率的变化达到不同含水状态下的残余强度。传统应变软化模型不能准确表达这一变化过程中滑带土残余强度的动态特征, 而引入动态残余强度的应变软化模型能更加真实地模拟含水率变化时滑坡稳定性的发展。基于此,文章对四川中江县垮梁子滑坡开展了野外调查工作,通过现场竖井获取滑带土,采用环剪试验研究了滑带土力学参数与含水率的关系,在此基础上建立了基于动态残余强度的应变软化模型,模拟了垮梁子滑坡在滑带土处于不同含水率阶段的发展情况。结果表明:含水率的增加使得滑带土抗剪性能显著衰减,峰值及残余抗剪强度呈近乎线性降低,残余强度参数则表现出三次函数型衰减特征。应用基于残余强度参数衰减规律建立的应变软化模型模拟了垮梁子滑坡的变形破坏过程,结果表明在滑带土含水率低于20%时,斜坡仅在前缘局部产生塑性区;当含水率达到22%时,斜坡中上部开始产生塑性区及未贯通滑动面;当含水率达到24%时,塑性区趋于贯通,滑坡进入加速变形状态,并于坡表产生张拉裂缝;当含水率达到26%时,滑坡处于失稳状态,坡表张拉塑性区及破坏面的发展与滑坡现状破坏特征高度吻合。该成果可为相关滑坡的稳定性研究提供一定的理论依据。     

滑坡运动过程仿真分析

滑坡是一个动态过程，滑坡体的运动是一个集滑动，转动，拉张等运动方式的复杂运动过程，传统的极限平衡和计算和有限元分析均无法描述滑坡的运动学特点和运动过程。非连续变形分析（DDA）是最近发展起来的一种新的离散数值分析方法。该方法基于块体的运动学理论及数值分析，可以开展块体的静力和动力学计算。应用非连续变形分析方法对长江三峡区新滩滑坡的运动全过程进行了数值模拟研究，模拟方案充分依据该滑坡的地质，地形特征，按不同岩土体和地质结构面类型进行块体单元的划分，共划分成504个块体单元。模拟结果表明，新滩滑坡是以斜坡中部姜家坡一带的局部破坏为其运动的开始阶段，并进一步牵引上部滑体和推动下部滑体。代表性块体单元的位移变化曲线和滑动速度变化曲线反映了滑动过程中滑坡体块体系统的变形是非连续的，各处块体的动态形态各异，从而很好地再现了新滩滑坡的整个动态过程，揭示了滑坡的运动机制。     

Analysis of the bedding landslide due to the presence of the weak intercalated layer in the limestone

Analysis and research results show that the sliding plane of Jiudingshan landslide is along the weak intercalated layer (clay-filled) in the limestone and the sliding block is separated by the tension crack on the slope crest. The earlier study results show that for the rough, ups and downs structural plane, when i is greater than 2.0, the shear strength of the structural surface is intensely close to the strength of the filling. By the earlier theory, this failure must be through the clay filling. In this study, the failure is back-analyzed and the shear strength of the infilling is tested by the laboratory direct shear tests for which samples were retrieved in the field. The failure cannot be explained by the laboratory results of shear strength parameters. To simulate the field conditions, the real strength parameters of sliding surface are measured by the in situ shear tests for the weak intercalated layer. By the in situ tests, it is shown that the failure initiates along the contacts between the clay infilling and the limestone boundaries, but not through the clay itself. Though the contact surface is the interface of the clay–limestone, the cohesion is not 0 and it is not negligible too.     

Kita-Uebaru natural rock slope failure and its back analysis

A large landslide occurred in Kita-Uebaru (or Asato) area of Nakagusuku village in Okinawa Island (Japan) on 10 June 2006 after a rainy period of about 9 days. The total rainfall was 126 mm from June 8 till the time of the landslide this period. This landslide destroyed several buildings and roads, and the total travel distance of the landslide was about 110 m. In this article, the authors were concerned with the initiation conditions of Kita-Uebaru landslide and post-failure motions of the landslide body. The observations made in the landslide area, structural geology analyses and outcomes of geotechnical investigations are described first. Then, possible causes of the landslide are investigated through back analyses using as inputs the geological structure and the strength properties of planes of discontinuities involved in the sliding processes. The final part of the article is concerned with the simulation of post-failure motions of the landslide body. The results of the investigations and back analyses indicate that the failure plane was bi-planar and the heavy torrential rainy period for about 3 days was the main cause of initiation of the landslide. The mechanical model presented in this article was capable of capturing the overall features of the landslide body following the initiation of the failure.     

坡脚开挖诱发古滑坡复活的机制分析

黄土地区存在许多古滑坡体,由于滑后土体土质疏松,裂隙发育,在坡脚开挖作用下极易发生变形破坏,造成大量财产损失,同时也对开挖施工安全构成了极大的威胁,因此对坡脚开挖诱发古滑坡复活的失稳机制的研究十分迫切和必要。以延安市王窑村滑坡为例,通过室内试验分析了三轴应力环境下围压、含水量对土体变形破坏的影响,并运用数值模拟研究了开挖过程中最危险滑面上的应力及强度变化趋势,揭示了坡脚开挖诱发古滑坡复活的变形破坏机理。研究结果表明:坡脚开挖改变了坡体中下部的应力分布,抗滑段土方开挖减小了滑坡抗滑力,增大了下滑力,最终滑坡下滑力超过抗滑力,导致古滑坡复活。