库区水位下降对库岸边坡稳定性的影响

为了研究库区水位下降过程中岸坡的稳定性,在探讨库岸边坡稳定性影响因素的基础之上,通过数值计算与稳定性分析理论,同时考虑坡度、坡体渗透系数与库区水位下降速率的不同工况条件下渗流场中孔隙水压力的变化,并对库区水位下降期间各因素变化对边坡稳定性系数的影响进行了分析.研究结果表明:库区水位下降对库岸边坡的稳定性有着较大影响,是库区边坡失稳破坏的重要因素,当水位下降时,库岸边坡稳定逐渐降低.采用FLAC对不同工况进行数值计算,当研究参数取值在符合工程实际范围内时,相同水位下降速率条件下库岸边坡坡度逐渐增加时,边坡稳定性呈现逐渐下降趋势;坡体渗透系数逐渐减小时,边坡稳定性也越来越低.而不同的水位下降速率对边坡稳定影响也不同,当水位下降高度相同时,下降速率逐渐增大则边坡的稳定性逐渐降低;坡度、水位下降速率与坡体渗透系数的变化都会导致边坡稳定系数的变化,其中库区水位下降过程中存在着稳定性系数最小值,水位下降速度越大,最小值越小;此外,库水位下降时存在一个最危险水位,此时坡体稳定性系数最小,而该水位大致位于坡体下1/3处.研究结果对三峡库区水库水位的调控和库岸边坡的稳定性具有一定的工程意义.     

水位升降对粘土心墙土石坝渗流稳定性分析

利用非饱和非稳定渗流理论,对某粘土心墙土石坝在水位不同升降速度条件下的渗流场进行了数值试验,分别设计了从0.0 m开始以2.51、.5 m/d的水位上升速度蓄到88.0 m正常蓄水水位的计算工况,以及从88.0 m正常蓄水水位分别以8.0、4.0、2.0 m/d水位下降速度泄水至10.0 m最低水位的计算工况,计算了各工况下粘土心墙土石坝的渗流场,对比分析了水位升降速度对坝体渗流场的影响.基于上述渗流计算成果,分析了各工况下土石坝上游、下游面坝坡的稳定性,总结了坝坡最危险滑动面的时空演化规律和安全系数随水位升降速度的变化规律,为水库调水和日常管理提供了参考.     

基于矢量和法的库水位下降边坡稳定性研究

为了研究库水位的下降对高陡边坡稳定性及变形的影响,以锦屏一级水电站左岸边坡为例,基于饱和渗流理论,以左岸坝头滑移破坏模式为研究对象,利用矢量和稳定性评价方法研究不同库水位下降速度对锦屏一级电站左岸边坡的稳定性影响规律。研究表明:当库水位以1 m/d的速度由1 880 m高程下降至1 800 m高程时,左岸坝头滑移破坏模式的安全系数由1.214降低到1.147,且安全系随着库水位下降趋于稳定,而当库水位下降速度达到2 m/d时,安全系数的降低速度随着库水位的下降逐渐加剧,当库水位达到1 800 m高程时,安全系数降至1.052,左岸坝头滑移破坏模式接近临界状态;库水位下降条件下坡体最大位移处发生在坝头滑移破坏模式潜在滑动面的剪出口位置。     

抛填饱和粉质黏土夹淤泥质土围堰稳定性分析

江西信江双港航运枢纽采用导流明渠开挖的饱和粉质黏土夹淤泥质土进行围堰填筑,施工过程中,水下围堰由明渠浚挖土直接采用挖泥船进行水上抛填,饱和粉质黏土受浚挖和抛填双重扰动,强度低且堰体内分布极不均匀,不仅围堰难于成型,且运行期内易发生堰坡失稳。为了评估这类围堰堰坡的稳定性、探究水位涨落条件下抛填饱和粉质黏土围堰边坡的变形破坏模式,采用有限元软件PLAXIS对信江双港航运枢纽上下游围堰开展不同水位及不同水位升降速率条件下的稳定性计算分析;针对抛填形成的围堰土体强度变化范围大、受环境影响明显的特性,开展堰坡稳定性的敏感性分析,同时,基于安全系数接近于1.0时的坡体最大侧向变形随时间的变化曲线,提出堰体稳定自动监控的预警和报警值。结果表明：采用坡度为1：4~1：5的平缓围堰边坡,通过设置反压平台,围堰在正常水位涨落条件下处于稳定状态;抛填土的强度降低会诱发滑动体从背水面坡脚贯通到堰顶;由于抛填饱和粉质黏土围堰的强度低和不均质性,为确保围堰稳定,须进行侧向变形、渗压及降雨量监测实时监控预警;抛填饱和粉质黏土围堰侧向变形报警值和预警值宜取1.5~2.0、1.1~1.5 mm/d。     

防渗体形式对土坝除险加固工程渗流稳定的影响

从渗流和边坡稳定的角度出发,论述了土坝加固工程中防渗体形式和尺寸选择的条件和要求,结合工程实例给出了土坝加固工程中不同防渗体形式(厚度、位置)对坝体渗流和稳定的影响数值计算结果和规律,特别介绍了土坝防渗体形式对土坝边坡逸出坡降、边坡稳定性的影响.计算结果表明:不论是考虑稳定渗流还是非稳定渗流,土坝防渗墙位置越靠近上游坝坡,防渗效果越好;防渗墙设置越厚,防渗效果越好.以期本结论对于工程设计提供一定的借鉴和参考.     

高土石围堰施工-运行过程边坡稳定性分析

高土石围堰边坡稳定性与堰体材料的力学性质密切相关.在围堰施工及运行过程中,随着结构应力和渗流状态的变化,堰体材料力学参数也发生持续性变化.基于围堰施工过程中堰体应力及渗流状态变化规律分析和土石材料力学非线性理论,建立考虑施工过程的土石围堰边坡稳定分析模型;在此基础上,进行高土石围堰施工-运行过程边坡稳定特性分析,结果表明堰体边坡稳定的最不利工况出现在基坑开挖后的堰前水位下降期,最危险滑动面位置随着水位下降速率的增加由背水面转向迎水面;当水位下降速率一定时,堰坡稳定安全系数呈先减小后增加趋势,最小值及其出现时间与水位下降速率相关.     

水位变动速度对某库区岸坡堆积体稳定性的影响

水位变动期间库区岸坡堆积体渗流场及稳定性的变化是一个动态过程,如何评价水位变动速度对堆积体稳定性的影响是工程上一个重要课题。采用有限元计算与刚体极限平衡分析相结合的方法,探讨了水位变动速度对堆积体渗流场及稳定性的影响机理和规律,研究成果表明,水位变动速度对堆积体在水位变动期间瞬时渗流场有着较大的影响,较大水位上升速度对堆积体稳定性有利,但水位下降速度增大对堆积体稳定性不利,水位下降速度由0.5增大至5 m/d,堆积体稳定性系数可降低15%～20%,水位下降期间堆积体危险水位往往出现在堆积体坡脚以上1/3～1/5坡高处。     

降雨入渗对煤系膨胀土边坡瞬态稳定性影响分析

采用非饱和瞬态渗流有限元与极限平衡法相结合,对降雨入渗过程中煤系膨胀土边坡的渗流场与稳定场进行数值模拟,分析了土体渗透系数、降雨强度、降雨持时以及坡比等参数变化对煤系膨胀土边坡稳定性的影响。研究结果表明,土体渗透系数对边坡安全系数有较大影响,渗透系数较大的边坡在降雨48 h后,其安全系数出现陡降,最大降幅达到27. 82%。降雨强度越大,相同降雨持时的边坡安全系数越小,安全系数的降幅也越大。坡比对煤系膨胀土边坡的安全系数有显著影响,边坡安全系数随着坡比的减小而增大,在降雨强度为8. 33"10-7m/s的情况下,建议该类型土质边坡的坡比取值为1∶1. 5～1∶1. 75。     

饱和渗透系数空间变异性对边坡稳定性的影响

基于随机场理论和非饱和渗流理论,通过对某一假想边坡在降雨条件下进行非饱和渗流分析和边坡稳定性分析,研究了在不同降雨强度下土体饱和渗透系数的空间变异性对边坡稳定性的影响.分析结果表明,随着降雨强度的增加,边坡稳定性降低,临界降雨强度与饱和渗透系数有关.饱和渗透系数的竖向波动尺度对边坡稳定性影响较大,目前采用确定性分析方法对渗流过程模拟存在风险.     

降雨和库水位升降条件下考虑非饱和渗透系数空间变异的边坡可靠度分析

降雨和水位升降对库岸边坡具有显著影响,传统确定性分析难以准确评估其稳定性。考虑降雨和水位升降联合作用下水力参数的空间变异性,进行非饱和土边坡可靠度分析具有重要意义。以赣江库区中的莒洲岛边坡为研究对象,以贝叶斯方法校准的多元水力参数的联合随机场为基础,建立非饱和土边坡的稳定性分析方法。根据有限的岩土力学室内试验数据,采用贝叶斯方法校准土水特征曲线的模型参数,并从VGM、VGB、VG和FX模型中选出最优模型;联合多元水力参数的随机统计特征,生成非饱和土边坡渗透系数的随机场空间分布;针对2021年5月赣江水位快速升降并伴随暴雨的工程背景,将上述方法应用于莒洲岛库岸边坡的稳定性分析。研究结果表明,暴雨与水位变化的联合作用对边坡安全系数的影响显著,确定性分析的边坡安全系数偏低,考虑非饱和渗透系数空间变异性后计算所得到的SWCC综合可靠指标不能满足规范要求,需采取额外的边坡工程加固措施以保证边坡的长期稳定性。     

基于非饱和大孔隙流双重介质模型的浸水边坡水力响应数值模拟

受地形限制,大量公路、铁路等常出现沿库与沿河线,水位变化是引起库岸滑坡的重要因素。目前边坡渗流研究多集中在非饱和均匀流,对大孔隙边坡非平衡流方面研究仍显滞后。为此,以福建省某一典型库区边坡为例,对比了水位上升时考虑非饱和渗流和非饱和大孔隙流时边坡水分场和稳定系数随时间的变化规律,并分析了水位上升速率（v）、大孔隙域水力传导系数（Ksf）、两域交界处水力传导系数（Ksa）、土粒中心至大孔隙边界距离（a）、大孔隙体积占比（wf）等对大孔隙边坡稳定系数的影响规律及权重。研究结果表明：水位上升中,非饱和渗流下边坡内部基质域含水率明显小于非饱和大孔隙渗流下边坡内部基质域含水率。非饱和渗流条件下边坡浅层向内的水力坡度明显大于非饱和大孔隙流边坡且大孔隙边坡中相同位置基质域含水率远大于大孔隙域（最大达18.9倍）。两种渗流工况下,边坡稳定系数随水位上升均呈现先减小后增大的趋势,并于同一水位（在最高蓄水位高程的一半附近）同时达到最小值。相同渗流工况下,且考虑非饱和大孔隙渗流边坡比考虑非饱和渗流边坡稳定系数更小。增加v、Ksf、a、wf或减少Ksa,坡内两域间水分交换减弱,水分将快速运移至坡体深处,引起地下水位上升,促使边坡稳定性最大降幅达17.7％。v、Ksf和wf对边坡稳定影响占权重较大且相当,Ksa和a所占权重较小且约为前者一半。     

Mechanism analysis of landslide of a layered slope induced by drawdown of water level

1 Introduction The instability of slopes on the river banks and the reactivation of ancient slopes, in- duced by drawdown of water level, are great danger for the local residents and for thehydroelectric engineering. A lot of accidents or disasters relating to the drawdown of water level can be found in literatures. In October 1963, the landslide, near the recently constructed Vajont Reservoir dam at that time, caused the failure of the toppest hyper- bolic arching dam in the world, ruined on…     

A new apparatus for investigating stress, deformation and seepage coupling properties of rock fractures

A true triaxial apparatus which is composed of three units was presented. The apparatus allows for investigations on deformation and seepage behaviors of a single rock fracture subjected to lateral stress and normal stress. The first unit has three jacks which can apply loads independently in three orthogonal directions. The second unit is used to supply water inflow, control seepage pressure and measure flow velocity in real time. The third unit is for measuring the normal deformation of rock fractures. Some tests for investigating the normal deformation and seepage behaviors of rock fractures subjected to normal and lateral loads on hard granite specimens with an artificial persistent fracture, were introduced. The results show that both the normal deformation and the hydraulic conductivity are influenced not only by the normal stress but also by the lateral stress. It is also shown that the aperture and the hydraulic conductivity decrease with the increasing normal stress but increase with the increasing lateral stress and both the aperture and the hydraulic conductivity obey exponential relationships with the normal stress and the lateral stress.     

Q mechanism analysis of landslide of a layered slope induced by drawdown of water level

The frequent drawdown of water level YanYangtze River will greatly influence the stability of the widely existing slopes in the Three Gorges reservoir zone, especially those layered ones. Apart from the fluctuating speed of water level, the different geological materials will also play important roles in the failure of slopes. Thus, it must be first to study the mechanism of such a landsllide caused by drawdown of water level.A new experimental setup is designed to study the performance of a layered slope under the drawdown of water level. The pattern of landslide of a layered slope induced by drawdown of water level has been explored by means of simulating experiments. The influence of fluctuating speed of water level on the stability of the layered slope is probed, especially the whole process of deformation and development of landslide of the slope versus time. The experimental results show that the slope is stable during the water level rising, and the sliding body occurs in the upper layer of the slope under a certain drawdown speed of water level. In the process of slope failure, some new small sliding body will develop on the main sliding body, and the result is that they speed up the disassembly of the whole slope.Based on the simulating experiment on landslide of a layered slope induced by drawdown of water level, the stress and displacement field of the slope are calculated. The seepage velocity, the pore water pressure, and the gradient of pore water head are also calculated for the whole process of drawdown of water level. The computing results are in good agreement with the experimental results. Accordingly, the mechanism of deformation and landslide of the layered slope induced by drawdown of water level is analyzed. It may provide basis for treating this kind of layered slopes in practical engineering.     

Response of an old landslide to reservoir filling: A case history

1 Introduction It is generally believed that reservoir slope instability is mainly caused by unfavorable hydrodynamic evolution in the bank due to reservoir filling and/or operation. Many cases of instability were reported both in China and abroad, causing life fatalities and economic losses, and even leading to project abandonment[1-5]. Riemer[5] reviewed 60 published case histories and indicated that 85% of slide events happened during con- struction and/or filling period, or within 2 years …     

初始渗流场对渣土场边坡降雨入渗特征及其稳定性的影响

渣土场是容纳弃土和弃渣的主要场所,由于堆填材料和压实方法的差异性,研究初始渗流场对计算渣土场边坡的降雨入渗特征及其稳定性的影响具有现实意义.以深圳市部九窝渣土场边坡为研究对象,运用非饱和渗流原理和非饱和土强度理论建立数值计算模型,设计了不同初始渗流条件和不同降雨强度的计算方案,揭示了渣土场边坡在降雨作用下的渗流特征及其...     

Response of an old landslide to reservoir filling: A case history

Unfavorable hydrodynamic evolution is considered as the major cause leading to reservoir slope instability and is often modeled by numerical method. However, this simulation is seldom checked by systematic field instrumentation. Taking the opportunity of filling the Three Gorges Reservoir, a system was established in Xietan landslide to monitor reservoir water level, subground water level, seepage pressure, rainfall and deformation, etc. The monitored data during reservoir filling shows that: (1) The water level rise in the bank lags behind the reservoir filling and the lag time depends on the bank permeability; (2) rainfall-induced subground water rise and its lag time is closely correlated to hourly rainfall, indicating that it is not feasible or sufficient to use daily rainfall for analysis; (3) the effect of inverse seepage during reservoir filling on stability is ephemeral and reservoir filling is the major cause leading to bank instability.