共查询到20条相似文献，搜索用时 171 毫秒
1.
An investigation and remediation of instability along upstream cut slopes for an earthfill dam in differentially weathered rock in southern Turkey is described. The major instability problem was a 45-m high and 200-m long previously cut slope next to the main axis of the dam, above the diversion tunnels and water outlet structures. The slope was first designed and excavated in 1986 based on the temporary berm approach. Rising water level in the reservoir would change the shear strength parameters and the pore-water pressure in the slope; thus, probable deep failure would damage the entrance of the diversion tunnels and water outlet structures, as well as the earthfill embankment of the dam. In June 1996, the slope face was re-excavated and protected against wave erosion by placement of a layer of rock riprap over a layer of bedding and a filter material. A strong earthquake (MS = 6.2) occurred during a period of rapid drawdown in 27 June 1998. The slope remained stable, although numerous tension cracks developed in Quaternary terrace deposits near the reservoir area. 相似文献
2.
库（河）岸边坡由于坡体迎水面水位下降经常造成坡体稳定性降低,建立快速评估水位变化条件下的边坡稳定性分析方法具有重要的工程实用价值。基于库（河）水位下降过程及坡体内非稳定渗流条件,通过对ABAQUS程序进行二次开发,发展了考虑地表水-地下水联动作用下的黏性土边坡强度折减有限元分析方法;在分析边坡土性参数、相对渗透比值、边界条件对边坡稳定性影响的基础上,建立了考虑土性参数、相对渗透比值、库水位下降比、坡角等一体化的相对稳定安全系数综合图表表示方法。该方法能够简便、快捷地查出实际涉水边坡在不同工况下的稳定安全系数及设计边坡坡比,可作为现有图表法的有益补充。 相似文献
3.
库水位变化对库岸边坡稳定性的影响 总被引：3，自引：0，他引：3
在假定坡体孔隙水水位为水平线且不考虑渗透作用影响的基础上,基于极限平衡法考察了水位上升及下降的快慢对边坡安全系数的影响。对比计算表明:在水位缓慢变化即坡体内外水位线等高的条件下,边坡的安全系数随着水位坡高比的增大先略减小后急剧增大,且在水位坡高比为0.3处取得最小值,在边坡完全淹没于水中时取得最大值。当边坡完全淹没于水中后,水位高于坡顶的多少对边坡安全系数没有影响;在水位骤降或陡升条件下,相同库水位对应的边坡安全系数基本上均小于水位缓慢变化情况下的安全系数,故工程实际中无论是排水还是蓄水,都应尽量保持水位缓慢变化,这样才能使边坡处于较安全的状态。 相似文献
4.
Modeling uncertainty in stability analysis for design of embankment dams on difficult foundations 总被引：2，自引：0，他引：2
A probabilistic 3-D slope stability analysis model (PTDSSAM) is developed to evaluate the stability of embankment dams and their foundations under conditions of staged construction taking into consideration uncertainty, spatial variabilities and correlations of shear strength parameters, as well as the uncertainties in pore water pressure. The model has the following capabilities: (1) conducting undrained shear strength analysis (USA) and effective stress analysis (ESA) slope stability analysis of staged construction, (2) incorporation of field monitored data of pore water pressure, and (3) incorporation of increase of undrained shear strength with depth, effective stress, and pore water pressure dissipation. The PTDSSAM model is incorporated in a computer program that can analyze slopes located in multilayered deposits, considering the total slope width.
The main outputs of the program are the geometric parameters of the most critical sliding surface (i.e., center of rotation/radius of rotation and critical width of failure), mean 2-D safety factor, mean 3-D safety factor, squared coefficient of variation of resisting moment, and the probability of slope failure. The program is applied to a case study, Karameh dam in Jordan. Monitored data of induced pore water pressure in the dam embankment and soft foundation were gathered during dam construction.
The stability of Karameh dam embankment and foundation was evaluated during staged construction using deterministic and probabilistic analysis. Foundation stability was evaluated based on the monitored data of pore water pressure.
The study showed that the mean values of the corrective factors which account for the discrepancies between the in situ and laboratory-measured values of soil properties and for the modeling errors have significant influence on the 2-D safety factor, 3-D safety factor, slope probability of failure, and on the expected failure width.
The degree of spatial correlation associated with shear strength parameters within a soil deposit also influences the probability of slope failure and the expected failure width. This correlation is quantified by scale of fluctuation. It is found that a larger scale of fluctuation gives an increase in the probability of slope failure and a reduction in the critical failure width. 相似文献
5.
Influential factors in evaluating the construction pore pressure in earth dams by using UDAM program
The aim of this article is to discuss about the influential parameters affecting the state of the pore pressure within the low permeability section of an earth dam body during the periods of construction, immediately after construction, and also during some times elapsing after construction. Because the condition of soil in constructing earth dams is usually unsaturated, so the matter of unsaturated soils should be considered here and a special finite element program suitable to this topic needs to be applied. The finite element program used in this study is the UDAM finite element program which has been compiled specifically for illustrating the behavior of unsaturated soils. The results of the UDAM computations are discussed in view of the pore water pressure developed within the body of dam slope during the stages of construction, and its maximum positive values immediately after the construction and its variations in the post-construction times are shown. Because the positive pore pressure decreases the shear strength of soil and the negative pressure (i.e. suction) increases the strength, the state of slope stability is correlated with the influential factors which can affect the situation of pore pressure distribution within a given section. Therefore, based on the present computations, the effect of height of embankment, initial degree of saturation, coefficient of permeability, degree of compaction and finally the effect of elapsing time are illustrated. 相似文献
6.
《Geomechanics and Geoengineering》2013,8(1):49-55
Stability of levees is critical to the safety of human and structures, especially at high water levels. Levees may fail due to the existence of soft soil foundations or seepage of water through the levees or rapid drawdown. Deep mixing technology has been considered one of the good alternatives to solve foundation and seepage problems while geosynthetics can be used to stabilize slopes during rapid drawdown. Studies have shown that deep mixed columns and geosynthetics can increase the stability of highway embankments over soft soils. In those studies, however, no ponding water exists on either side of the embankment, which is not the case for levees. Experimental studies have shown that deep mixed columns under a combination of vertical and horizontal force could fail due to shear or tension/bending or rotation. A finite difference method, incorporated in the FLAC (Fast Lagrangian Analysis of Continua) Slope software, and a limit equilibrium method (specifically Bishop's method), incorporated in the ReSSA software, were adopted in this study to investigate the stability of the levee with ponding water or under rapid drawdown. In this study, deep mixed columns were installed in continuous wall patterns, which were modeled as 2D deep mixed walls. Geosynthetic layers were modeled using cable elements with grout properties between geosynthetic and soil in the numerical analysis. Mohr-Coulomb failure criteria were used for the levee, the soft soil, and the deep mixed walls. The stability of a levee at different stages (end of construction, average service condition, high water surge, and rapid drawdown from the service condition and the highest water level condition) was examined. The study clearly demonstrated that the deep mixed walls can enhance the stability of the levee by providing shear/moment resistance and hindering seepage through the levee and geosynthetics can enhance the riverside slope stability of the levee by providing tensile resistance to the soil. 相似文献
7.
Embankment dams are important and costly civil engineering structures that provide an essential infrastructure for the management of water. One of the critical aspects of dam design is the analysis of stability and safety of the earth structure under various operating and environmental conditions. Traditionally, a deterministic approach is used for such analysis. However, the determination of variables such as soil strength parameters, pore pressure and other pertinent properties involves uncertainties, which cannot be handled in the traditional deterministic methods. It is, therefore, highly desirable to develop a reliability based analytical/numerical methodology for stability analysis of dams taking into account these uncertainties. Reliability and probability theories are developed in this paper for assessing the reliability index and the corresponding probability of failure of multi-layered embankment dams and slopes. Two definitions were used to calculate the reliability index (i.e. the normal distribution and the log–normal distribution). The computer program
was developed and validated by the Congress Street open cut failure case. The developed approach was used to study the stability of the King Talal embankment dam. The results are discussed and conclusions drawn. 相似文献
8.
J. Amnyattalab H. Rezaie 《International Journal of Environmental Science and Technology》2018,15(12):2625-2636
Stability of an earth dam is affected by different factors of which the most important is seepage. One of the factors in defining the seepage rate is hydraulic conductivity coefficients in suctions and various moistures in earth dam body in which different models of soil–water retention curves are used to be defined. In this study, first the soil–water retention curves of van Genuchten and Brooks–Corey models are used to predict the soil–water retention of different body layers of 2 dams. Then, hydraulic conductivity coefficients are calculated through Mualem and Burdine’s models. Water seepage rate and the stability of dams were calculated in two phases: I. construction finalization prior to intaking water and II. rapid drawdown of water. Bishop and Morgenstern–Price methods are used to analyze the stability of dams. The stability and seepage results demonstrate that simultaneous use of Brooks–Corey’s soil–water retention curve with Mualem’s method results in the highest seepage rate in comparison with van Genuchten’s model in case of variable n, m and Burdine hydraulic conductivity. Safety factors achieved from both cases of construction finalization prior to intaking water and rapid drawdown of water demonstrated the accuracy and reliability of hydraulic coefficient prediction. 相似文献
9.
Horizontal drains have been commonly used in stabilising unsaturated residual soil slopes. This study examines the effectiveness of horizontal drains in stabilising residual soil slopes against rainfall-induced slope failures under a tropical climate. The study includes field instrumentation at two residual soil slopes complemented with a parametric study relating to drain position. Field monitoring results indicate that rainfall infiltration is limited to a certain depth below which infiltration becomes insignificant. This zone tends to be unsuitable for horizontal drains. Horizontal drains were found to be most effective when located at the base of a slope. The parametric study indicated conditions under which horizontal drains are effective or ineffective in improving the stability of a slope. It was also found that horizontal drains have little role in minimising infiltration in an unsaturated residual soil slope. Benefits of using horizontal drains can be obtained through the lowering of the water table. 相似文献
10.
基于分层边坡在水位涨落时发生滑坡的模拟实验,简要描述了实验中的主要现象,计算了实验模拟的分层坡体内与水位变化直接相关的动态渗流场、孔隙水压力场与渗透速度场分布。根据计算结果,对水位变化导致坡体变形失稳的机理进行了分析,为这类分层边坡滑坡的治理提供了依据。 相似文献
11.
Effects of horizontal drains on slope stability under rainfall by three-dimensional finite element analysis 总被引：1，自引：0，他引：1
The effects of the horizontal drains on the ground water level during rainfall are predicted using a three-dimensional finite element analyses of transient water flow through unsaturated–saturated soils. The slope stability is evaluated by the global safety factor, based on the three-dimensional elasto-plastic shear strength reduction finite element method. The following conclusions are obtained: (1) the horizontal drains can effectively lower the ground water level and increase the slope stability under rainfall, but the rate of the increase in the safety factor becomes smaller and smaller when the drains is extended beyond a critical length; (2) lengthening the horizontal drains is more effective than making the spacing smaller and increasing the number of the drains in a group in order to lower the ground water level and increase the slope stability; (3) the effects of the drains are mainly influenced by the ratio of the rainfall intensity to the saturated hydraulic conductivity. © 相似文献
12.
The current state of art for limit equilibrium analysis of slope stability problems lacks a satisfactory procedure for stability evaluation under general, rapid (undrained) loading conditions. Some procedures are available for the analysis of rapid drawdown, but these suffer from several shortcomings and, furthermore, are not applicable to other types of rapid loading. An approach is presented which overcomes these limitations. The approach integrates four components-establishment of soil behaviour on the basis of laboratory testing, estimation of steady-state conditions in the slope using a boundary value analysis, estimation of distribution of undrained strength in the slope using undrained stress paths, and identification of the critical slip surface followed by calculation of its factor of safety. The approach is illustrated through its application to the stability analysis of an earth dam under rapid drawdown and earthquake conditions. 相似文献
13.
如何保持新旧路基间的变形协调是拓宽工程中普遍关注的问题,目前尚缺乏对于拓宽方式对软土路基工程特性影响的直接对比分析。本文开展离心模型试验,采用普通填料或气泡轻质土进行放坡或挡墙拓宽,分析了新旧路基变形、地基土中孔压和土压力在路基拓宽后的变化规律。试验结果表明,气泡轻质土显著减小拓宽过程中产生的孔隙水压力增量和附加应力增量。相较于边坡拓宽,挡墙拓宽方式对地基影响更小。轻质土路堤采用挡墙拓宽方式引起的挡墙倾角和墙背土压力均较小。采用Boussinesq公式计算得到的拓宽路堤引起的地基中附加应力分布与实测值基本吻合,且偏于保守。本文的研究成果对指导路基拓宽工程具有借鉴意义。 相似文献
14.
研究可以同时考虑渗流、变形与稳定的非饱和土质边坡稳定性分析方法具有重要的理论意义及工程实用价值。基于Fredlund双应力变量理论进行非饱和非稳定渗流-应力耦合分析,同时与传统非耦合渗流方法确定的孔压场进行对比发现,两种方法确定的浸润线变化过程相近,堤底处孔压的最大相对误差为8.8%,验证了耦合分析结果的可靠性。将基质吸力对强度的贡献纳入黏聚力中得到坡体强度参数的空间分布规律,又基于滑面强度参数时空分布规律借助Matlab平台开发了非稳定渗流条件下非饱和土质边坡稳定性的矢量和法分析程序。以库水位下降条件下堤坡的稳定性分析为例,将不同方法的计算结果进行对比,发现文中方法搜索得到的滑面位置相对于传统方法要深缓,但总体位置相差不大,不同方法对应的安全系数相差不足0.096,验证了所提方法的合理性。 相似文献
15.
库水位下降时的岸坡非稳定渗流问题研究 总被引：5，自引：1，他引：4
水位下降时岸坡的渗流是涉及土体由饱和向非饱和状态过渡的水-气二相流过程,目前相关研究成果大都假设孔隙气压力为0,忽略孔隙气的影响。根据水、空气的质量守恒定律和达西定律,结合多相流理论建立水-气二相流模型,采用高效的积分有限差分法求解,通过变换主要变量,实现饱和（单相）与非饱和（二相）的相互转变,并给出各种边界条件下合理的数学处理方法。通过Muskat渗流问题,验证了上述模型的正确性;并对某土质岸坡水位下降时的非稳定渗流问题进行分析,结果表明,岸坡的基质吸力小于浸润线以上的负孔隙水压力,在浸润线以上的很大区域为毛细管水饱和带,其土体饱和且基质吸力为0,这对边坡稳定十分不利,精确分析水位下降的边坡稳定问题时,孔隙气压力变化的影响值得研究。 相似文献
16.
基于Richards方程,对坝体的饱和-非饱和渗流场进行了模拟,再根据饱和-非饱和渗流场和非饱和土抗剪强度公式,对坝体的稳定性进行了分析。结果表明,水位骤降过程中坝体的安全系数通常呈现先缓慢增加后迅速减小的变化过程,分析坝体失稳时塑性区和位移场发现,水位下降的初期,坝体左侧坡体的安全系数要低于坝体右侧坡体,但水位下降到一定程度,右侧坡体的安全系数迅速减小,并先于左侧坡体失稳;采用有限元强度折减法用于多坡面边坡稳定分析时,只能获得最小安全系数的包络线;心墙具有隔水防渗的作用,对水位变化渗流具有阻尼作用。 相似文献
17.
洪水浸泡和水位骤降情况下黄河下游堤防堤岸稳定性分析 总被引：1，自引：0，他引：1
水库库岸边坡稳定在水位骤降工况下的研究目前已比较成熟,但对黄河下游堤防在水位骤降工况下的堤坡稳定状态却研究甚少。通过选取黄河下游标准化堤防某段堤岸边坡为研究对象,建立有限元渗流模型,提出黄河下游堤防的水位骤降速度标准,同时分析了在水位骤降速度为2、4、5 m/d时的坡内浸润线变化、堤岸稳定性变化,以及在水位骤降组合洪水浸泡最不利工况下的堤岸稳定状态。通过分析,给出水位下降情况、水位下降组合浸泡情况下的堤岸稳定状态图,并从图中可以查出在某一水位下降速度、洪水水位降至某一高程处的堤岸稳定状态,为工程人员在堤防建设中运用和推广提供了便利。 相似文献
18.
Tsunami runup and drawdown can cause liquefaction failure of coastal fine sand slopes due to the generation of high excess
pore pressure and the reduction of the effective over burden pressure during the drawdown. The region immediately seaward
of the initial shoreline is the most susceptible to tsunami-induced liquefaction failure because the water level drops significantly
below the still water level during the set down phase of the drawdown. The objective of this work is to develop and validate
a numerical model to assess the potential for tsunami-induced liquefaction failure of coastal sandy slopes. The transient
pressure distribution acting on the slope due to wave runup and drawdown is computed by solving for the hybrid Boussinesq—nonlinear
shallow water equations using a finite volume method. The subsurface pore water pressure and deformation fields are solved
simultaneously using a finite element method. Two different soil constitutive models have been examined: a linear elastic
model and a non-associative Mohr–Coulomb model. The numerical methods are validated by comparing the results with analytical
models, and with experimental measurements from a large-scale laboratory study of breaking solitary waves over a planar fine
sand beach. Good comparisons were observed from both the analytical and experimental validation studies. Numerical case studies
are shown for a full-scale simulation of a 10-m solitary wave over a 1:15 and 1:5 sloped fine sand beach. The results show
that the soil near the bed surface, particularly along the seepage face, is at risk to liquefaction failure. The depth of
the seepage face increases and the width of the seepage face decreases with increasing bed slope. The rate of bed surface
loading and unloading due to wave runup and drawdown, respectively, also increases with increasing bed slope. Consequently,
the case with the steeper slope is more susceptible to liquefaction failure due to the higher hydraulic gradient. The analysis
also suggests that the results are strongly influenced by the soil permeability and relative compressibility between the pore
fluid and solid skeleton, and that a coupled solid/fluid formulation is needed for the soil solver. Finally, the results show
the drawdown pore pressure response is strongly influenced by nonlinear material behavior for the full-scale simulation. 相似文献
19.
Stability of an embankment constructed on soft consolidating soil improved with pre-fabricated vertical drains is investigated. The factor of safety of the embankment is obtained at various time intervals from the end of construction till the end of consolidation in order to check the embankment stability. Finite element method is used to obtain the effective stresses at required points in soil at various time intervals. Critical slip surface is obtained using two methods. In the first method, the critical slip surface is assumed as an arc of a circle selected among various probable slip circles with minimum factor of safety whereas, in the second method, a random walking type Monte Carlo technique is used to predict the critical slip surface. The effects of providing vertical drains on stability of an embankment is investigated by comparing the factor of safety of slope with vertical drains to the factor of safety of slope without vertical drains. It is concluded from the study that the installation of vertical drains enhances the factor of safety of the embankment from the end of construction till the end of consolidation. 相似文献
20.
Xuecheng Gao Hanlong Liu Wei Wang Zhenyu Wang 《Georisk: Assessment and Management of Risk for Engineered Systems and Geohazards》2019,13(2):145-153
To investigate the influences of reservoir water level drawdown on slope stability, a series of numerical simulations were carried out to examine the impacts of slope angle, slope permeability and water drawdown speed on the pore water pressure (PWP) change during seepage, as well as the factor of safety (Fs) of the slope. Based on the numerical results, an estimation model relating the factor of safety to the influential factors mentioned above was developed. The model expression indicates that there are interaction effects between the slope angle, the drawdown speed and the slope permeability, with regard to the influences on slope stability. Furthermore, in view of the uncertainty characteristics of the slope permeability, reliability assessment was performed to examine the influences of those key parameters mentioned above on the probability of slope failure. 相似文献