三峡库区靠椅状土质滑坡变形特征及机制分析

自三峡库区蓄水以来,库区不少滑坡监测位移–时间曲线呈台阶状阶跃变化,靠椅状土质滑坡尤为明显,此现象加大了滑坡稳定状态的识别度,严重影响滑坡的预警预报。以白家包滑坡为例,通过多次野外地质调查、长期现场巡查、十多年的GPS位移监测数据、1a多全自动监测数据及滑坡学相关理论等,较深入研究了在库水升降及降雨条件下该滑坡的变形演化规律。结果表明,在汛期及库水位升降时滑坡发生变形,库水位下降为诱发变形的主要因素,年位移量在35～250 mm,历年位移曲线呈"W"型波动,一次跃阶30～180 mm位移量集中在20～30 d完成。库水位下降25m水位高程为150m左右时,位移跃阶启动。库水位下降至145m后1周,跃阶日位移达最大值5～8mm/d。降雨只在库水位下降期间对滑坡的变形有一定的助推效果,在库水位上升期间,几乎没有影响。受靠椅状等坡体结构特征制约,在库水位升降作用下坡体会反复变形,但难以发生整体性大破坏。     

基于诱发因素响应与支持向量机的阶跃式滑坡位移预测

受库水位周期性调度和降雨的影响,三峡库区部分滑坡的位移变形呈台阶状。针对滑坡的这种变形特征,提出一种基于诱发因素响应分析的进化支持向量机位移预测模型:应用移动平均法将滑坡总位移分解为趋势项位移和周期项位移,趋势项位移变化受坡体地质条件控制,应用多项式函数进行预测;周期性位移变化受诱发因素联合控制,选取变形主导因素作为影响因子建立进化支持向量机模型进行预测;将分项位移预测值叠加即为总位移预测值。以库区典型阶跃式滑坡——八字门滑坡为例,应用进化支持向量机模型进行预测研究。结果表明:诱发因素响应分析是滑坡位移预测的关键;基于诱发因素响应的进化支持向量机耦合模型在阶跃式变形期有较好的预测效果,是一种行之有效的阶跃式滑坡位移预测方法。     

川主庙滑坡变形特征与稳定性评价研究

三峡水库蓄水后大量涉水老滑坡产生复活变形,其中川主庙滑坡是三峡库区典型滑坡之一。根据宏观地质调查及专业监测资料,分析了滑坡变形演化特征,得到了滑坡变形的影响因素及变形机制,砂泥岩互层的软弱地层为滑坡的复活变形提供了物质基础,良好的地形则为滑坡持续变形提供了微地貌条件,降雨与库水位作用则加剧了滑坡变形,通过理论分析与数值模拟计算可知,滑坡复活变形的最主要影响因素则是降雨,其次的作用,导致坡体稳定性下降从而产生变形,该滑坡目前处于基本稳定状态,若加大库水位下降速率,则处于不稳定状态,研究结果为滑坡防治以及水库调度提供了依据。     

拉马古滑坡前部局部复活变形特征及成因分析

在分析拉马古滑坡变形特征的基础上,对古滑坡体前部局部复活成因进行了深入的研究,研究表明,古滑坡体前部局部复活的最重要原因是美姑河连年对滑坡前缘的冲刷与坡体上丰富的水系对滑坡体的诱发作用,其次滑坡体物质组成为滑坡体复活创造了基础.     

三峡水库水位涨落条件下奉节南桥头滑坡稳定性分析

三峡大坝建成后，水库将分期蓄水抬高水位，蓄水后库区水位将上抬100多米。由于防洪的需要，库水位将在175～145m范围内变动。库水位的抬升和周期性涨落，将改变岸坡原有的水．岩作用环境与条件，有可能引起库岸边坡与滑坡的失稳。南桥头滑坡位于三峡库区奉节县长江公路大桥南岸，其稳定性直接关系到大桥的安全运行。应用FLAC^4.0对南桥头滑坡在不同水位及涨落条件下的渗流场与应力场进行分析，研究应力-渗流耦合作用下滑坡体的变形趋势与破坏特征：探讨了不同蓄水工况下滑坡稳定性的变化规律及其对桥基的影响。结果表明：南桥头滑坡在现状条件下处于基本稳定状态；三峡水库蓄水后，随着水位的抬升，滑坡整体稳定性逐渐恶化；滑带内塑性区全部连通，滑坡安全系数小于1．0，表明该滑坡在库水位抬升后有可能产生整体失稳。建议采取有效的工程治理措施，消除滑坡对大桥运行造成的安全隐患。     

长江三峡区八字门滑坡稳定性分析与评价

在研究了三峡库区秭归县八字门滑坡的工程地质条件及滑坡体基本特征的基础上,介绍了该滑坡的结构及变形特征,从滑坡形成条件和诱发变形因素两方面分析了滑坡形成的原因及诱发坡体失稳的主要因素.在不同工况下及地震作用下对滑坡体进行稳定性计算,结果表明,在库水位变化和暴雨情况下滑坡处于不稳定状态,极有可能复活.     

降雨与库水位变动下堆积体滑坡稳定性分析

库水位变化、暴雨骤降等环境因素是引起库岸边坡失稳的重要因素,针对金沙江库岸付家坪子滑坡,采用有限元软件Geo-Studio,分析库水位变化、降雨及其共同作用等环境因素对岸坡稳定性的影响规律。结果表明:在一个库水位调度周期内,付家坪子滑坡的最危险时刻为库水调度下降至540 m时(5月),整体滑坡欠稳定,最不稳定的位置是滑坡前缘;在库水位调度周期内滑坡安全系数变化与库水位变化趋势基本一致,库水位不变时,地下水位线上升导致岩土力学参数降低,安全系数减小;库水位上升时,库水入渗产生渗流力和对岸坡的静水压力,大于滑坡前缘被淹没后产生的浮托力,安全系数增大。随着库水位的降低,滑坡体的稳定性下降,说明坡内的渗流力和滑坡前缘所受的库水压力起主导作用。     

清江隔河岩水库茅坪滑坡复活机理初探

基于对茅坪滑坡体1993～2000年的降雨、水库水位、变形等监测资料的综合分析，初步认为茅坪滑坡体复活是其东侧白岩危岩体中不合理的采煤活动引起的。采煤活动诱发的危岩体开裂和崩塌，加强了滑坡体与危岩体的水力联系，间接扩大了滑坡体的受雨面积。因此，从滑坡体变形的影响因素上讲，降雨（特别是强降雨）的影响转大，水库蓄水和库水位波动的影响范围主要集中在滑坡体前缘。     

降雨作用下三峡库区某粘质土滑坡优势流分析

三峡库区复活型滑坡多为粘质土型,自三峡水库蓄水以来,在降雨及库水的周期性作用下,该类滑坡均出现不同程度的拉裂现象。由于库水位上升,可能导致该类滑坡稳定性降低,处于临界状态,这类滑坡是否失稳,将取决于大气降雨。常规数值模拟时,一般默认滑坡土体为各向同性渗透材料,没有考虑裂隙的优势渗流,其结果通常与实际情况不符。本项研究考虑采用各向异性渗透材料对滑坡在降雨作用下进行渗流场及位移场的模拟,并与常规模拟及监测数据进行对比。发现考虑材料各向异性渗透系数时,滑坡体孔压分布及位移变化均与实际情况接近,说明了该简化优势流模型的可靠性。     

水库滑坡变形特征和预测预报的数值研究

水库滑坡不同于一般山体滑坡,其稳定性受水位波动的影响十分明显。由于水库滑坡的特殊性和重要性,其变形特征和预测预报的研究已成为目前研究的热点和难点。库水水位的波动,改变了水库滑坡的水力边界条件,引起坡体内渗流场的非稳定渗流,采用传统的分析方法很难对其变形破坏特征和稳定性的动态变化进行研究,并对其失稳破坏进行预测预报。因此,基于数值极限分析方法对水位下降过程中滑坡体的变形特征和稳定性的动态变化规律进行了研究;通过位移-时间关系曲线以及位移-时间对数关系曲线对滑坡体的变形破坏特征进行了定量研究,并提出利用水平位移陡升段（加速段）和水平方向的夹角作为滑坡临滑预报的判据,为认清水库滑坡的破坏机制和提升其预报水平提供了新的思路。     

Probabilistic stability analysis of Bazimen landslide with monitored rainfall data and water level fluctuations in Three Gorges Reservoir,China

Landslide is a common geological hazard in reservoir areas and may cause great damage to local residents’ life and property. It is widely accepted that rainfall and periodic variation of water level are the two main factors triggering reservoir landslides. In this study, the Bazimen landslide located in the Three Gorges Reservoir (TGR) was back-analyzed as a case study. Based on the statistical features of the last 3-year monitored data and field instrumentations, the landslide susceptibility in an annual cycle and four representative periods was investigated via the deterministic and probabilistic analysis, respectively. The results indicate that the fluctuation of the reservoir water level plays a pivotal role in inducing slope failures, for the minimum stability coefficient occurs at the rapid decline period of water level. The probabilistic analysis results reveal that the initial sliding surface is the most important area influencing the occurrence of landslide, compared with other parts in the landslide. The seepage calculations from probabilistic analysis imply that rainfall is a relatively inferior factor affecting slope stability. This study aims to provide preliminary guidance on risk management and early warning in the TGR area.     

库水位下降对滑坡稳定性的影响

三峡水库2003年蓄水后，滑坡将可能成为三峡库区最严重的地质灾害之一，库水位下降和暴雨是导致滑坡的主要因素。根据三峡库水位调控方案考虑库区极端暴雨情况，利用有限元模拟库水位在175～145m波动和降雨时红石包滑坡Ⅲ的暂态渗流场，将计算得到的暂态孔隙水压力分布用于滑坡的极限平衡分析，并考虑基吸力对非饱和土抗剪强度的影响。探讨不同降雨速度、降雨条件对滑坡稳定性的影响。研究表明：库水位下降对滑坡稳定性的影响受控于滑坡土的入渗能力和滑坡结构形态，当暴雨强度为300mm／d时，红石包滑坡Ⅲ的临界降速1m／d。其成果将为库区滑坡治理提供科学依据。     

Creep model for unsaturated soils in sliding zone of Qianjiangping landslide

The mechanical behavior of sliding zone soils plays a significant role in landslide. In general, the sliding zone soils are basically in unsaturated state due to rainfall infiltration and reservoir water level fluctuation. Meanwhile, a large number of examples show that the deformation processes of landslides always take a long period of time, indicating that landslides exhibit a time-dependent property. Therefore, the deformation of unsaturated soils of landslide involves creep behaviors. In this paper, the Burgers creep model for unsaturated soils under triaxial stress state is considered based on the unsaturated soil mechanics. Then, by curve fitting using the least squares method, creep parameters in different matric suction states are obtained based on the creep test data of unsaturated soils in the sliding zones of Qianjiangping landslide. Results show that the predicted results are in good agreement with the experimental data. Finally, to further explore the creep characteristics of the unsaturated soils in sliding zones, the relationships between parameters of the model and matric suction are analyzed and a revised Burgers creep model is developed correspondingly. Simulations on another group of test data are performed by using the modified Burgers creep model and reasonable results are observed.     

三峡库区某滑坡稳定性时域分级评价

结合三峡库区某滑坡全自动专业地表位移长期监测资料,利用小波分析等数学方法半定量地探究在降雨和库水位两个因素作用下滑坡的运动演化过程,分月测值、日测值、时测值逐步细化的分级模式综合评价滑坡的稳定性及变形特征。结果表明:此评价法能客观、全面的反映滑坡稳定性的现状和发展趋势,对同类滑坡的研究具有借鉴意义;现阶段该滑坡处于潜在不稳定状态,库水位上升时抑制滑坡变形(较为微弱),下降时促进滑坡变形,并且这种影响一般会滞后一个星期左右。降雨量与滑坡变形成正相关,两种因素叠加作用时,变形速率显著增加。     

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.

     

滑坡位移预测的SVR-MIV变量筛选方法研究

支持向量回归机(Support Vector Regression, SVR)在滑坡位移预测研究中已得到广泛应用,但SVR具有模型可解释性差的缺陷,即无法直接获得并筛选最佳预测变量,从而影响预测精度。为此,将较广泛应用于评价神经网络模型变量影响大小的平均影响值(Mean Impact Value, MIV)方法与SVR模型相结合,实现基于SVR-MIV的变量筛选,该方法不但能对所有预测模型初始变量影响大小进行排序,还可以进一步结合反向逐变量剔除分析实现变量筛选。为验证该方法的有效性,选择三峡库区两类典型水库滑坡代表的累积位移监测数据,在采用移动平均法将位移分解为趋势项和波动项的基础上,重点针对波动项位移,选择包括降雨及库水位变动特征在内的12项初始变量,采用SVR-MIV方法进行变量筛选分析。结果表明,该方法筛选出的变量理论上符合对应滑坡变形影响机理分析结论,且可以提高滑坡位移实际预测精度。     

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.