利用颗粒流离散元素法研究台湾遽变式滑坡的运动和堆积模式

<正>山崩和滑坡的分布在全球非常普遍,往往对民众造成生命与财产极大的损失,仅1992至2001年间,山崩和滑坡造成全球超过9000人死亡;台湾位于欧亚大陆板块与菲律宾板块的交接处,为当今世界上最活跃的造山带之一,地块极为年轻和不稳定,地震频繁,加上每年夏秋二季的台风侵袭,因此山坡地上极易发生大型遽变式的滑坡事件。台湾近年来最令     

颗粒流离散元在滑坡运动过程模拟中的应用

介绍了颗粒流离散元的分析原理,以某岩质边坡为实例,构建了计算模型。根据实际资料,在计算模型中加了节理,节理的力学参数弱于岩体。在下方的抗滑挡土墙完全失去作用的情况下,用此模型对该滑坡的运动过程进行了计算预测,分析了整体的变形、不同部位的位移和应力等运动特点,上部粉质粘土区系拉裂引起的下滑,下部碎石土区因挡墙损坏而产生沿节理面的滑动,但拉应力变化不大。指出了在该滑坡存在2个滑动面,并针对2个滑动面提供了相应的治理建议。     

基于离散单元法的滑坡堆积及其涌浪计算

采用离散单元法对水库库岸边坡的动态破坏过程进行了研究,给出了计算流程并开发了相应的软件。介绍了离散单元法的基本原理,分析了常用的计算滑坡速度方法的不足及用离散单元法的优势,基于离散单元法提供的块体运动信息并结合波动方程模拟了滑坡体滑入水库时所激起的涌浪。此外,采用离散单元法研究了滑坡的堆积形状。通过算例验证了方法的可行性与程序的正确性。算例结果表明：块体在坡面上运动时,用离散单元法计算得到的块体的速度和能量法与潘家铮法一致,且更方便、更高效;由于涌浪的叠加,多个块体所激起的涌浪高度比单个块体的涌浪高一些,这表明在进行涌浪分析时,考虑多块体的涌浪叠加效应是至关重要的,滑坡的堆积形状为滑坡的灾害评估提供了依据。通过自行开发的离散单元法软件模拟了块体的滑动和涌浪的产生及其传播过程,其模拟结果为研究边坡的滑动破坏的启动、破坏过程及滑坡的风险评价提供了新的思路。     

云南黄坪库区滑坡运动及其失稳模式的离散元模拟

在蓄水库区,伴随着水库蓄水及可能发生的暴雨天气,往往容易触发库岸坡岩土体失稳,这不仅影响工程建设的实施,还对拦河大坝和周围人民群众的生命财产安全造成严重威胁。本文以溪洛渡水电站黄坪滑坡为例,在野外现场调查的基础上,分析了其滑动的成因和机制,并利用离散元法对其三维滑动过程进行模拟,深入分析了滑坡失稳后的运动状态及规律。结果表明:滑坡体运动过程中,其表面会发生较大变化,且滑坡体会呈现出中间失稳体积较大,两侧失稳体积较小的特征;滑坡内部颗粒分布会发生改变,存在大颗粒运动至滑坡体表面,小颗粒运动到滑坡体底面的现象;滑坡体颗粒的速度和压力在不同位置也会发生改变,存在不同颗粒间速度相差很大,滑坡体内压力分布不均匀的情况;滑坡体颗粒的运动速度、运动距离表现出从后缘到前缘,同一横剖面中表层至底层由大到小分布的规律。     

基于颗粒流方法的堆积层滑坡运动过程模拟

以颗粒流离散元为研究方法对勉县杨家湾十组堆积层滑坡破坏方式与运动过程进行数值模拟研究。通过PFC^2D双轴模拟试验所标定的岩土体宏观模拟参数与室内试验所获取的宏观实测参数进行对比,确定堆积层滑坡所需的颗粒细观参数,然后将标定的细观参数代入堆积层滑坡模型,对滑坡破坏方式及运动过程进行模拟研究。结果表明：滑坡破坏在初始阶段蠕滑变形累积,滑坡体挤压坡脚,直至坡脚产生剪切破坏,并向上牵引发展,使得滑坡整体顺接触面破坏下滑并堆积于坡脚,表现为典型的牵引式渐进破坏,结果与实际情况基本吻合。研究认为,采用颗粒流方法对堆积层滑坡破坏与运动过程的模拟研究具有较高的适用性,对该类滑坡防治具有一定的参考意义。     

基于离散元的高速远程滑坡运动堆积特征及 能量转化研究 ——以三溪村滑坡为例

高速远程滑坡-碎屑流运动速度、堆积特征和能量转化是研究其致灾机制的重要因素,而模型试验、野外调查并不能全面揭示其成灾机理。文章以三溪村滑坡为例,采用PFC3D离散元模拟方法,揭示滑坡运动过程中的前部、中部和后部岩土体的速度演化分布、堆积特征和能量转化关系。研究结果表明:三溪村滑坡的残余摩擦系数为0.2时,模拟结果与实际堆积特征一致。前部、中部、后部岩土体到峰值速度存在差异,前部岩土体速度分布表现为显著的单峰型特征,而后部岩土体速度分布为双峰型特征。滑坡不同部位的岩土体堆积呈现层序分布;滑坡重力势能的转化中,摩擦耗能占总能量的52%,动能峰值时刻仅有15%的重力势能转化为动能。研究结果可为高速远程滑坡的运动机理分析和防灾减灾治理工程提供重要参考。      

颗粒流强度折减法和重力增加法的边坡安全系数研究

将强度折减法和重力增加法的思路引入离散单元法,对土坡安全系数的评价作尝试性研究。运用颗粒流软件,采用强度折减法和重力增加法对边坡进行稳定分析。结果表明颗粒流计算得到的结果与有限元和条分法计算结果比较接近,为计算边坡稳定开辟了一条新的途径。采用颗粒流求解边坡的安全系数不需要条分,也即不需要对条间力做假定,同时不需要假定滑移面的位置和形状,颗粒根据所受到的接触力调整其位置,最终从抗剪强度最弱面发生剪切破坏。最后对强度折减法的不等比例折减提出了不同观点,为今后的研究提供思路。     

红石岩特大岩质滑坡成因和破坏模式的离散元分析

岩质边坡发生滑动不仅与其坡体结构、构造发育有关,还与外界动力因素相关。2014年云南鲁甸发生的M_S6.5地震造成多处大型滑坡及特大型滑坡,而同年云南景谷M_S6.6地震中却只造成了中小型滑坡。为了查明鲁甸地震造成大型滑坡的主要原因,本文以2014年鲁甸地震诱发的红石岩特大型滑坡为例,利用颗粒流PFC^2D离散元软件对其进行数值分析,采用软硬两种平行黏结模型解决拉压比失真的问题,分析层理、坡顶卸荷裂隙、潜在滑动面、坡体风化裂隙、地震等各因素作用下的滑坡成因和破坏模式。根据正交试验结果和坡体裂纹发展情况,探讨了地震诱发红石岩滑坡的破坏模式以及影响红石岩滑坡规模的主要因素。结果表明,在地震作用下,红石岩发生特大规模滑坡的原因为深部滑动面的形成;而深部滑动面的形成主要来源于自身由上而下的'硬-软-硬’结构的影响;红石岩特大型滑坡的失稳破坏模式可以概括为：中部软岩和边坡浅表破坏-硬岩悬空-剪切带的形成-大规模崩滑-堆积。本文的研究对地震诱发含软弱夹层反倾岩质滑坡灾害的预防、评估及治理有着一定的理论和工程指导意义。     

灾难性地震和降雨滑坡的体积与运动距离研究

为预测和评价灾难性滑坡的致灾机制,基于国内近年来地震和降雨诱发的灾难性滑坡资料,对地震和降雨滑坡的等价摩擦系数H/L、最大水平运动距离L、最大垂直运动距离H与滑坡体积V的关系进行分析。研究灾难性地震和降雨滑坡的远程运动特征以及不同规模滑坡最大水平运动和垂直运动的优势距离。研究结果表明,滑坡的H/L、L、H与V具有幂律关系,其中H/L与V具有负幂律关系,L、H与V具有正幂律关系。同一规模等级的地震和降雨诱发灾难性滑坡的水平和垂直运动距离不同。以H/L＝0.42作为滑坡远程运动的标准,地震诱发的灾难性滑坡与滑坡远程运动的关系较小,而降雨诱发灾难性滑坡与滑坡的远程运动的关系较大。根据滑坡运动距离的累积分布表,以80%滑坡的运动距离所分布的范围,建立了滑坡不同规模等级的优势运动距离区间,同规模等级的地震滑坡和降雨滑坡在水平和垂直运动的优势距离区间上存在差异。灾难性滑坡的运程不仅受滑坡体积的控制还与其诱发机制相关,其研究成果可为由地震和降雨诱发的灾难性滑坡的致灾区域和致灾强度的预测和评价提供参考依据。     

岩质滑坡−碎屑流的运动距离计算公式研究

滑坡?碎屑流的远程运动距离是碎屑流体所能够达到的最大堆积距离,是灾害预警和评估的重要指标。通过总结已有碎屑流运动距离研究成果,从岩体势能入手开展研究,并结合量纲分析,首先建立了运动距离与势能之间的基本方程。其后,采用4种颗粒材料开展岩质碎屑流滑槽试验,研究碎屑体体积V、滑移区坡度?、碎屑粒径d以及最大垂直运动距离H等对碎屑流运动距离L的影响,通过逐步拟合回归,建立了基于势能的岩质滑坡?碎屑流最大水平运动距离的计算公式。最后,采用汶川地震触发的38个岩质碎屑流以及17个其他典型岩质滑坡碎屑流数据对计算公式进行了验证,结果表明,考虑该运动距离计算公式具有较好的可靠性,能够为山区滑坡?碎屑流灾害预警工作提供理论指导。     

Kinematics and internal deformation of granular slopes: insights from discrete element modeling

The kinematics and internal deformation of a failure mass during the flow-like moving off a slope were monitored and quantified with the particle flow method in this study. Two kinds of cases were investigated, noncohesive and cohesive granular slopes. Three different internal friction angles and cohesive strengths were considered to systematically investigate their effect on the kinematics and internal deformation of the failure mass. We analyzed the movement within the failure mass and concluded that the mass moves downwards in an undulating pattern. The slope surface topography changes from a straight line to curved lines with slope breaks in a convex geometry. In addition, dilatation within the failure mass, which deforms internally and heterogeneously, is strongly dependent on its mechanical properties. A larger mass moves downslope, and the mass moves faster and further in the model with lower internal friction and cohesion. The internal friction and cohesion have a positive impact on porosity and two-dimensional (or volumetric in 3D) strain within the failure mass.     

The characteristics and mechanisms of the recent catastrophic landslides in Africa under IPL and WCoE projects

This paper described the recent catastrophic landslides in Sierra Leone, DR Congo, and Nigeria and their probable mechanisms. The landslides occurred at the peak of rainy season on steep mountains predisposed to failure by geologic, climatic, hydrologic, and tectonic factors. The landslides killed over 500 people and displaced more than 2000 people. The DR Congo landslide occurred a few days after the Sierra Leone landslide of August 14, 2017. The Sierra Leone mudslide occurred in the Regent area of Freetown on the steep slopes of Mount Sugar Loaf. Sugar Loaf forms a part of extensive and forested highlands south of the city. The cities of Freetown, Lokoja in Nigeria, Conakry in Guinea, and other cities in Africa have grown in recent times to almost encircle vulnerable highlands that are prone to failure. The internal friction angles of the slope materials were low at all saturation and normal stress levels used in the study. The result correlated with the stability analysis which showed that the factor of safety along the potential sliding surfaces was at critical value at failure. The number of casualties following a slip of the weak slope materials increased because of the housing pattern and the lack of effective drainages in urban cites in Africa. These factors are important considerations for future prevention and mitigating measures aimed at saving Africa from catastrophic slope failures.     

Some catastrophic landslides since the twentieth century in the southwest of China

Landslides occur frequently in China. Especially, in the western part of China, large-scale landslides are notable for their scale, complex formation mechanism, and serious destruction. This paper presents some typical large-scale landslides that occurred in the southwest of China since the beginning of the twentieth century but were rarely reported worldwide. These cases represent different geological conditions and different triggering factors and mechanisms. The analysis shows that about 80% of large-scale landslides occurred in the first slope-descending zone along the eastern margin of Tibet Plateau, which is tectonically very active. The intensive interactions between the endogenic and epigenetic geological process cause serious dynamic change on the high steep slope and then result in the development of large-scale landslides. Strong earthquakes are also common in this area, and repetitive seismic activities make the slopes unstable and more vulnerable to failures. Besides earthquake, the area also experiences high rainfall, which is also responsible for triggering some of the large landslides.     

Laboratory experiments on three-dimensional deformable granular landslides on planar and conical slopes

Landslides of subaerial and submarine origin may generate tsunamis with locally extreme amplitudes and runup. While the landslides themselves are dangerous, the hazards are compounded by the generation of tsunamis along coastlines, in enclosed water bodies, and off continental shelves and islands. Tsunamis generated by three-dimensional deformable granular landslides were studied on planar and conical hill slopes in the three-dimensional NEES tsunami wave basin at Oregon State University based on the generalized Froude similarity. A unique pneumatic landslide tsunami generator (LTG) was deployed to control the kinematics and acceleration of the naturally rounded river gravel and cobble landslides to simulate broad ranges of landslide shapes and velocities along the slope. Lateral and overhead cameras are used to measure the landslide shapes and kinematics, while acoustic transducers provide the shape of the subaqueous deposits. The subaerial landslide shape is extracted from the camera images as the landslide propagates under gravity down the hill slope, and surface reconstruction of the landslide is conducted using the stereo particle image velocimetry (PIV) system on the conical hill slope. Subaerial landslide surface velocities are measured with a planar PIV system on the planar hill slope and stereo PIV system on the conical hill slope. The submarine deposits are characterized by the runout distances and the deposit thickness distributions. Larger cobbles are observed producing hummock type features near the maximum runout length. These unique laboratory landslide experiments serve to validate deformable landslide models as well as provide the source characteristics for tsunami generation.     

Diffuse instability of granular material under various drainage conditions: discrete element simulation and constitutive modeling

Acta Geotechnica - Diffuse instability is a typical failure mode of sand that occurs before the perfect plastic flow condition is attained. Whereas extensive laboratory experiments have...     

Predisposition and cause of the catastrophic landslides of August 2005 in Brienz (Switzerland)

Very intensive rainfall in August 2005 (>300 mm/3 days) triggered moderately deep (2–10 m) landslides of about 50'000 m³ volume each in two mountain torrent catchments above the village of Brienz (Berner Oberland, Switzerland). These landslides – originating in Trachtbach and Glyssibach catchments – transformed into extremely rapid (>5 m/s) debris flows, which caused significant damage in inhabited areas; two persons lost their lives and about twenty-five families became homeless. The Brienz case was the most damaging one among many landslide disasters occurring during those rainy days in the Swiss Alps. In this paper we study in detail the predisposition and causes of the 2005 landslides in the Brienz area, based on field mapping, analysis of high resolution images and digital terrain models, derived from LIDAR and infrared measurements taken before and after the event. The features of these landslides are compared with past and dormant landslides in the mid-slope portion of the mountain chain north of Brienz, which has been the source of many catastrophic mass wasting events during the last centuries. Detailed field mapping shows that highly weathered series of strongly overconsolidated Mesozoic marls (Diphyoides Limestone & Vitznau Marls of Valanginian age) and their residual soils form the primary source for the sliding materials. The rupture surfaces of the moderately deep landslides often run at the transition from saprolite to weathered bedrock, with a dip angle of about 40o in the landslide depletion area. These landslides transform into debris flows, where debris slides into strongly convergent hillslopes or directly into headwater channels.     

基于颗粒物质力学与连续介质热力学的岩土本构模型初探

首先简要介绍颗粒物质力学与模拟岩土材料本构特性的热力学方法,其次对力链及其对应的强弱网络的形成、力学特性与能量耗散特点与机制进行深入地分析,随后在Collins提出的土体热力学模型的基础上,考虑强弱网络结构的应力应变特征,引入合理的假设,探讨建立符合热力学原理的宏细观结合的岩土本构模型的思路与步骤