Vertical and horizontal displacements of a reservoir slope due to slope aging effect,rainfall,and reservoir water

Landslides are common hazards in reservoir areas and significantly affect dam operation and human lives.For the prevention and management of landslides,accurate assessment of the factors influencing their generation is essential.This study evaluated the key external factors influencing horizontal and vertical displacements of Luobogang Reservoir Slope in Hanyuan County,China.Displacements had been monitored by a surface-displacement-monitoring system consisting of 118 GPS stations during 2012-2015.To identify the external driving factors,their influence zones,and slope responses,we analyzed 32 months of displacement measurements and other multi-source datasets using the empirical orthogonal function.Overall,the results show that slope aging effect,rainfall,and reservoir water levels are three main driving factors.For horizontal displacement,aging effect is the most critical factor and predominantly affects the edges of landslides,the gob cave,and the public building zones.The secondary factor is the reservoir water level,which mainly acts on the boundary between the slope and reservoir water surface.The closer the slope zone is to the reservoir water,the more significant the impact is.Regarding vertical displacement,the most important factor is rainfall.The vertical displacement caused by rainfall accounts for 56.76% of the total vertical displacements.However,rainfall induces elastic displacements that generally cause less damage to the slope.The secondary factor is aging effect,and the vertical displacement caused by aging effect accounts for 9.42%.However,seven individual zones are highly affected by slope aging effect,which is consistent with the distribution of public buildings.

Deformation and failure mechanism of Yanjiao rock slope influenced by rainfall and water level fluctuation of the Xiluodu hydropower station reservoir

With the construction of the Xiluodu hydropower station on the Jinsha River,the reservoir impoundment began in 2013 and the water level fluctuates annually between 540 m and 600 m above sea level.The Yanjiao rock slope which is located on the left bank of the Jinsha River 75 km upstream of the Xiluodu dam site,began to deform in 2014.The potential failure of the slope not only threatens Yanjiao town but also affects the safe operation of the Xiluodu reservoir.This paper is to find the factors influencing the Yanjiao slope deformation through field investigation,geotechnical reconnaissance,and monitoring.Results show that the Yanjiao slope can be divided into a bank collapse area(BCA)and a strong deformation area(SDA)based on the crack distribution characteristics of the slope.The rear area of the slope has been experiencing persistent deformation with a maximum cumulative displacement(GPS monitoring point G4)of 505 mm and 399 mm in the horizontal and vertical directions,respectively.The potential failure surface of the slope is formed 36 m below the surface based on the borehole inclinometer.The bank collapses of the Yanjiao slope are directly caused by the reservoir impoundment while the deformation area of the slope is affected by the combination of the rainfall and reservoir water level fluctuation.Based on mechanism of the Yanjiao slope,prestressed anchor combined with the surface drainage and slope unloading are recommended to prevent potential deformation.

Effect of freeze-thaw cycles on soil engineering properties of reservoir bank slopes at the northern foot of Tianshan Mountain

The instability of soil bank slopes induced by freeze-thaw cycles at the northern foot of Tianshan Mountain is very common.The failure not only caused a large amount of soil erosion,but also led to serious reservoir sedimentation and water quality degradation,which exerted a lot of adverse effects on agricultural production in the local irrigation areas.Based on field investigations on dozens of irrigation reservoirs there,laboratory tests were carried out to quantitatively analyze the freeze-thaw effect on the soil engineering characteristics to reveal the facilitation on the bank slope instability.The results show that the softening characteristics of the stressstrain curves gradually weaken,the effective cohesions decline exponentially,the seepage coefficients enlarge,and the thermal conductivities decrease after 7 freeze-thaw cycles.The freeze-thaw effect on the specimens with low confining pressures,low dry densities and high water contents is more significant.The water migration and the phase transition between water and ice result in the variations of the soil internal microstructures,which is the main factor affecting the soil engineering characteristics.Sufficient water supply and the alternation of positive and negative temperatures at the reservoir bank slopes in cold regions make the water migration and phase transition in the soil very intensely.It is easy to form a large number of pores and micro cracks in the soil freezing and thawing areas.The volume changes of the soil and the water migration are difficult to reach a dynamic balance in the open system.Long-term freeze-thaw cycles will bring out the fragmentation of the soil particles,resulting in that the micro cracks on the soil surfaces are developing continuously.The soil of the bank slopes will fall or collapse when these cracks penetrate,which often happens in winter there.

A modified Hoek-Brown failure criterion considering the damage to reservoir bank slope rocks under water saturation-dehydration circulation

After water is impounded in a reservoir,rock mass in the hydro-fluctuation belt of the reservoir bank slope is subject to water saturationdehydration circulation(WSDC). To quantify the rate of change of rock mechanical properties, samples from the Longtan dam area were measured with uniaxial compression tests after different numbers(1,5, 10, 15, and 20) of simulated WSDC cycles. Based on the curves derived from these tests, a modified HoekBrown failure criterion was proposed, in which a new parameter was introduced to model the cumulative damage to rocks after WSDC. A case of an engineering application was analyzed, and the results showed that the modified Hoek-Brown failure criterion is useful.Under similar WSDC-influenced engineering and geological conditions, rock mass strength parameters required for analysis and evaluation of rock slope stability can be estimated according to this modified Hoek-Brown failure criterion.

Stability analysis of bank slope under conditions of reservoir impounding and rapid drawdown

Stability of an ancient landslide in a reservoir area is analyzed by using centrifugal model tests, soil laboratory tests and numerical analysis. Special attention is paid to variation in water level, simulation of large-scale heterogeneous prototype slope, and strength reduction of sliding zone soils after slope sliding. The results of centrifugal model test show that reservoir impounding can reduce sliding resistance at the slope toe, followed by toe collapsing and front cracking of slope. Rapid drawdown can produce hydrodynamic pressure towards reservoir at the front of slope. Deformation is observed in the middle and upper slope, which reduces the slope stability further and forms the pull-typed landslide trend. Reinforcement of slope toe is effective for preventing the progressive failure. The results of laboratory test show that slope toe sliding will lead to the redistribution of soil density and moisture content, which will reduce the shear strength of soil in sliding zone, and the cohesion of immersed soil is reduced gradually and finally vanishes with time. The numerical results show that the strength reduction method used in finite element method (FEM) is very effective in capturing the progressive failure induced by reservoir water level fluctuations, and the evolution of failure surface derived from numerical simulation is very similar to that observed in centrifugal model test.

Application of Vegetation Geosynthetic Technique to Slope Stability in the Three Gorges Reservoir

The vegetation geosynthetic reinforced slope is one of the new composite structures in civil engineering. It has a series of characteristics, such as low cost, convenient construction, optimal land utilization and flexible structure, and it has been widely used in hydraulic engineering, road, railway and harbor construction. The Three Gorges reservoir bank protection system is a challenging work. As the background, the interaction mechanism of soil and reinforced material has been studied. The test engineering is simulated by the numerical methods. The failure mechanism of the reinforced slope in the process is studied through analyzing the variation of the displacement, stress, plastic failure fields and factor of safety in the changing process of the water level. The reasonable evaluation of the protecting effect and bank slope stability is carried out. The research results could be used in the protective design and construction in the high slope in the Three Gorges reservoir region, and it also could provide reference to other protective engineerings in the littoral area.

Slope Reinforcement for Housing in Three Gorges Reservoir Area

The Three Gorges Project of the Yangtze River is the largest hydropower-complex project under construction in the world. Under the largescale relocation projects, 2874 engineered slopes are formed along with the construction of new towns. In this paper, the cutting slopes are mainly soil slopes and rock slopes. Soil slopes include residual soil slopes, colluvial accumulation slopes, swelling soil slopes, and artificial earth fill slopes, etc. Rock slopes include blocky structure rock slopes, layer structure rock slopes, and clastic structure rock slopes, etc. Varied protection measures have been used for slope protection in the reservoir area including shotcrete concrete-anchor bars, frame beams, retaining walls, slope stabilizing piles, sheet-pile walls, anchorage anti-shear tunnels, flexible protection grids, and drainage, etc. Besides, slope deformation monitoring systems have been set up to monitor deformation failure and the stability state of slopes. The protection measures have guaranteed slope safety and maintained a harmony with the urban environment and surrounding landscape.

A Study of Soil Nutrients in the Terrace Field Changed from Mountain Slope in Three Gorges Reservoir Region

In order to accurately grasp the soil fertility in Three Gorges Reservoir Region after changing mountain slope into terrace field,we take Wushan County for example,and use the spatio-temporal substitution method to analyze the soil nutrient status and trend about the terrace field changed from mountain slope under different length of implementation.The results show that the soil fertility is generally low in the study area,and according to the soil nutrient grading standards in the second national land survey,the average content of total nitrogen,available potassium,organic matter and available phosphorus reaches Standard III,Standard III,Standard IV and Standard V,respectively,and the spatial heterogeneity of soil nutrients is small.Compared to the sloping land,the terrace field changed from mountain slope has increasing soil nutrients on the whole with the length of farming.The mean of various indicators about soil nutrients in the terrace field changed from mountain slope for 2 years is lower than in the sloping land,and there is the biggest difference in soil fertility,while the mean of various indicators about soil nutrients in the terrace field changed from mountain slope for 14 years shows a linear upward trend,and the difference in soil fertility decreases.

玛西斜坡区风城组高含盐致密储集层流体识别

准噶尔盆地玛西斜坡区二叠系风城组发育碱湖沉积的高含盐致密储集层,其油水关系复杂,流体识别难度大。利用岩性扫描测井资料构建饱含盐水地层热中子宏观俘获截面,并利用测井热中子宏观俘获截面与饱含盐水地层热中子宏观俘获截面的差值构建含油性敏感因子,再利用氯元素相对产额与总孔隙度比值构建含盐度敏感因子,将含油性敏感因子与含盐度敏感因子交会形成流体识别图版。实例应用表明,利用该流体识别图版可以对储集层流体性质进行准确判断,为试油选层提供依据。

沾化凹陷垦西斜坡带沙河街组三段下亚段沉积特征及有利储层预测

垦西斜坡带构造处于沾化凹陷中部,孤岛潜山西南倾末端,西北为渤南洼陷,南边过垦西断层为三合村洼陷,是由孤西断层与一组近东西向垂直于孤西断层的断裂构建的“梳状断裂构造带”。研究区沙河街组三段下亚段油气充足,深部储层只要位于沟通油源的通道处,均有可能成藏。但早期研究认为该区沙河街组三段下亚段沉积类型为远源的三角洲水道沉积.

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。

基于降雨—库水作用下的某库岸堆积体滑带土力学性能及损伤模型研究

库水及降雨往复作用下滑带土的力学性能演化是库岸滑坡形成发展及破坏的内在控制因素。基于宏微观室内试验和理论分析手段,研究了干湿循环作用下滑带土性能的劣化机理及力学损伤特性,并建立了基于宏观强度的微观损伤演化模型。结果表明,随干湿循环次数的增加,滑带土内摩擦角和粘聚力均出现降低趋势,剪切强度劣化率随干湿循环扰动程度的增加而显著提高;亲水矿物及干湿循环下的水动力影响效应,使得土样微观结构由致密向疏松多孔转变,颗粒间微裂纹及原生孔隙迅速增加。基于损伤力学和室内试验提出的宏微观损伤模型可有效表征干湿循环作用下滑带土的劣化规律。

Reliability Analysis of Slope Stability Considering Temporal Variations of Rock Mass Properties

Temporal variation of rock mass properties,especially the strength degradation due to drying-wetting cycles as well as the acidic wetting fluid(rainfall or reservoir water)is crucial to stability of reservoir rock slopes.Based on a series of drying-wetting cycling and experiments considering the influences of pH values,the degradation degree models of the reduced cohesion𝑐𝑐′,friction angle𝜑𝜑′are developed.2D stability analysis of the slope is subsequently carried out to calculate the factor of safety(Fs)via limit equilibrium method(LEM)and a predictive model of Fs is built using multivariate adaptive regression splines(MARS),revealing the effect of the drying-wetting cycles and pH value.The reliability analysis by Monte Carlo simulation is performed to rationally consider the uncertainty and the temporal variation of the shear strength parameters of rock mass.Results indicate that the MARS-based model can estimate the Fs accurately.The Fs and the reliability indexβdecrease with increase of drying-wetting cycles,and the temporal variation of rock mass properties has significant influence on the slope reliability.Overlooking the temporal variation of rock properties may overestimate the Fs and reliability indexβin the longer term.

库水作用下深层倾倒变形体的失稳软化机制研究

在高山峡谷地貌和复杂脆弱的地质环境下,库岸边坡深层倾倒变形破坏现象成为了威胁水电工程安全运转的重大工程地质问题。近些年来随着越来越多大型、巨型水电工程建设与蓄水运行,深层倾倒变形体破坏问题逐渐凸显。这些深层倾倒变形体具有长期饱水(王雅雯,2016)、发育岩性为于遇水软化作用明显的软岩之中、滑坡演化时间长以及变形破坏模式为牵引式破坏(张成强,2018)等特点。综合以上特点.

大型水库区桥基边坡稳定性与失稳运动特征

我国西南山区已建成众多大型水库,库岸边坡在降雨、库水周期性涨落、地震等复杂地质条件作用下易发生滑坡。若公路桥梁基础位于库岸边坡变形或失稳影响范围内,可能对桥墩产生巨大的侧向荷载,从而危害基础结构乃至桥梁整体安全,而针对该问题研究较少。以白鹤滩库区小江特大桥桥基边坡为例,应用GeoStudio分析桥基边坡在库水涨落、降雨、地震联合作用下的稳定性;针对库水涨落联合降雨工况下的欠稳定边坡,采用TsunamiBalls(TB)数值方法模拟滑坡堆积体失稳下滑冲击桥墩的动力学过程,分析桥墩受到的动态冲击荷载。研究表明:(1)库水升降是影响边坡稳定性的主要因素;(2)施加地震荷载后边坡稳定性系数大幅降低,而降雨对稳定性系数影响有限;(3)滑体对桥墩的冲击荷载随时间先增大再减小,期间会出现3次主要荷载峰值,其中最大冲击荷载13890kN,出现在滑体最大运动速度之后,滑体冲击质量最大的时刻。库岸桥基边坡在库水位涨落条件下稳定性明显降低,TB模拟滑体失稳冲击过程可能造成桥基结构破坏。研究结果可为大型水库边坡和公路桥梁防灾减灾及安全运营提供技术参考。

深海能源土含气储层边坡稳定性研究

深海能源土开采不当往往会造成含水合物储层的强度劣化,诱发海床失稳问题。为探究深海能源土开采对含气储层边坡稳定性的影响,以深海能源土采挖回填装置的开采工况为实际工程背景,针对3种工况下能源土采挖回填诱发的海底滑坡现象,基于有限元强度折减法建立数值模型,分析不同黏土含量、含气量及回填加固等因素引起的水合物含气储层稳定性问题,得到相应安全系数。研究结果表明:黏土含量越高,海底沉积物边坡的安全系数越低,边坡稳定性越差;含气量对深海能源土含气储层的边坡稳定性呈非线性影响,安全系数随含气量的增加呈先上升后下降的趋势;采用胶结性材料进行回填加固处理可提高海底边坡安全系数,边坡稳定性增强。

Geo-Slope软件在小型水库大坝结构稳定分析中的应用

大坝结构稳定分析是大坝安全评价中的一项重要内容,为了能够快速、准确地计算和分析大坝结构稳定性,在大坝结构稳定性分析中应用了基于极限平衡法的Geo-Slope软件;以西安市蓝田县宋寨水库为例,论述了此软件的使用方法和分析过程,并依照相关规范规定,对不同工况组合下的计算结果进行了分析;得到了大坝上下游坡脚在不同工况条件下的安全系数,为大坝安全评价提供了可靠的理论依据;分析结果表明,Geo-Slope软件在处理小型水库大坝结构稳定性计算的过程中,具有计算速度快、精度高的优点,该软件可在小型水库大坝结构稳定分析中推广应用。

不同水位升降速率对库岸桥基边坡稳定性影响分析

为了研究库水位升降下桥基岸坡的稳定性,以西南地区某桥基岸坡为例,开展室内物理试验,并基于非饱和渗流理论,应用geostudio软件计算不同水位升降速率下桥基岸坡的渗流场、位移场与稳定性系数变化规律。结果表明:水位升降,坡内浸润线既有同步性,又有滞后性,滞后性随水位升降速率增大而增强。岸坡横向位移在水位升降时,先快速增加后缓慢减少,最大横向位移发生于桥基左侧岸坡上;水位升降速率增加,前期横向位移变化速率加快、变化幅度增大。桥基岸坡稳定性系数在水位上升时先快速增加后逐渐减小,在水位下降时先快速减小后缓慢增加。

EPSTM reservoir技术在斜坡区储层预测中的应用

以港西斜坡和官西斜坡为代表的黄骅坳陷斜坡区是大港油田滚动勘探潜力区带.古近系和新近系发育多种类型岩性储集体,开展精细储层预测是滚动勘探开发的关键.EPSTM reservoir是新一代储层预测软件,实现了储层预测与岩性解释一体化,在港西斜坡、官西斜坡储层预测中应用,取得较好效果.

准噶尔盆地中拐凸起东斜坡上乌尔禾组常规—致密油藏主控因素及成藏模式

准噶尔盆地中拐凸起东斜坡上乌尔禾组油气资源丰富,是效益勘探及建产的重要领域。应用测录井、生产测试及岩心分析化验资料,研究中拐凸起东斜坡上乌尔禾组储层特征,明确储层差异性的主控因素,建立中拐凸起东斜坡常规—致密油藏序次分布的成藏模式。结果表明:自北部向南部,研究区逐步由常规油藏转化为致密油藏,沉积作用是造成储层差异性的物质基础,控制储层岩性及原始物性,压实作用和浊沸石胶结作用加剧储层常规—致密差异演化;研究区成岩相带划分为泥质充填带、贫泥—弱胶结带、浊沸石胶结带和强压实—弱溶蚀带4种相带,其中贫泥—弱胶结带为有利储层发育带。该结果为研究区致密油藏勘探提供指导。