Investigating a reservoir bank slope displacement history with multi-frequency satellite SAR data

Slope instability arisen along with dam construction is a common problem of great concern in reservoir areas. Thus, displacement monitoring of active slopes is of great importance for the safety of dam operation. The unstable Guobu slope is located only about 1.5 km away from Laxiwa hydropower station in upstream Yellow River. In this study, Synthetic Aperture Radar (SAR) datasets acquired by C-band Environmental Satellite (ENVISAT) Advanced Synthetic Aperture Radar (ASAR), L-band Advanced Land Observing Satellite 2 (ALOS-2) Phased Array type L-band Synthetic Aperture Radar 2 (PALSAR-2), and X-band TerraSAR-X covering different evolution stages of Guobu slope were collected to investigate the displacement history so as to facilitate understanding of its deformation and failure mechanisms. The displacements occurred during the past decade were quantitatively identified for the first time by SAR pixel offset tracking analyses. The results show that before the reservoir impoundment, the maximum accumulative displacements on the slope were more than 7 m from 2003 to 2008, while the post-impoundment displacements also exceeded 7 m in just 1 year from September 2009 to September 2010. Furthermore, this slope is still in active deformation up to now. Nevertheless, the displacement rates seem decreased recently according to the interferometric results of TerraSAR-X data pairs from September 2015 to March 2016.     

Time evolution and spatial accumulation of progressive failure for Xinhua slope in the Dagangshan reservoir,Southwest China

This paper presents a preliminary study of time evolution and spatial accumulation of progressive failure for ancient landslide deposits in Xinhua slope. According to the geological response after impoundment, the Xinhua slope has shown the spatial accumulation of deformation, such as ground cracks in the rear edge, toe collapse, local shallow slides in intense rainfall, and progressive creep displacement. Approximately 2 years of monitoring was performed for the Xinhua slope with the assistance of the global navigation satellite system (GNSS), unmanned aerial vehicles (UAVs), and field investigations. The deformation process of a reservoir landslide is considered to be a comprehensive and complicated combination of geological influence from various adverse factors. Field investigations and monitoring indicate that the major serious influence after completion of dam construction comes from the initial large-scale impoundment, the fluctuation of water level, and the existence of a flood season. The creep/slip deformation of slope deposits is a result of integration with adverse hydraulic conditions, e.g., strong rainfall, intense currents and transient seepage flow inside the slope deposits, and activation by water level fluctuation, which can be verified from the twofold evident deformation in the flood season. For the reservoir with daily regulation ability, the occurrence of evident deformations in July highlights that the regulation plan for water level in the flood season is important for controlling the deformation of slope deposits, where the fluctuation of the water level is no more than 10 m in the operation period.     

基于卸荷岩体力学的大岗山坝肩边坡水平位移发育的多因素影响分析

在现阶段工程运用中,卸荷岩体力学理论中还需完善和扩充的几个方面为①锚索施加前后卸荷效应对边坡水平位移的影响;②超前开挖锚固滞后的方案会对具体工程岩体水平位移产生的影响;③关键工程结构面连通率对卸荷岩体位移的影响;④地震作用下卸荷岩体的水平位移响应;⑤地震作用下不同连通率对水平向位移的影响。针对此,以大岗山坝肩边坡为对象展开研究。分析指出岩体开挖卸荷后回弹变形和压缩变形都会大于未考虑岩质劣化时的计算变形。同时指出,卸荷条件下两种施工方案对坡面的水平向位移造成的影响较小,为超挖多级而锚固措施相对滞后的现场施工过程的可行性提供依据。统计出各剖面在不同高程水平位移随地震加速度发展特征,建议水平位移随地震加速度呈非线性变化区域为防震抗震重点加固区域。研究发现,连通率的增大会导致卸荷裂隙XL9-15,XL316-1的塑性区发育明显增大,而裂隙范围内塑性区的加剧不会明显地反映在坡面关键点的变化上,开挖工况可能造成表观位移较小的突发性崩塌。     

Deformation and mechanism of landslide influenced by the effects of reservoir water and rainfall, Three Gorges, China

Since the impoundment of the Three Gorges Reservoir in June 2003, numerous preexisting landslides have been reactivated. This paper seeks to find the factors influencing landslide deformation and the relationship between displacement and fluctuation of the reservoir water level, while the displacement and the intensity of rainfall based on monitoring data; 6 years of monitoring were carried out on the Shiliushubao landslide, a old landslide, consisting of a deep-seated main block and two shallow blocks, with a volume of 1,180 × 10⁴ m³ and located on the left bank of the Yangtze River, 66 km upstream of the Three Gorges dam. This landslide was reactivated by the impoundment and since then the landslide body has been experiencing persistent deformation with an observed maximum cumulative displacement of 8,598.5 mm up to December 2009. Based on the monitoring data, we analyzed the relationship between the fluctuation of the reservoir water level and displacement, rainfall and displacement, and found that the rainfall is the major factor influencing deformation for two shallow blocks and the displacement has a positive correlation with the variation of rainfall intensity. The fluctuation of the reservoir water level is the primary factor for main block, and the deformation rate has a negative correlation with the variation of reservoir water level, declined with the rise of the water level and increased with the drawdown of the water level.     

Field investigation of deformation characteristics and stress mobilisation of a soil slope

Stress mobilisation and deformation of a slope are important for engineers to carry out reliable design of retaining systems. However, most case histories reported mainly on the response of pore water pressure (PWP), whereas knowledge about the stress deformation characteristics of slope is limited. In this study, a saprolitic soil slope was instrumented to monitor not only the responses of PWP but also horizontal stress and horizontal displacement. To assist in the interpretation of field data, a series of laboratory tests was conducted to characterise volume change behaviour of the soil taken from the site, under the effects of both net stress and suction. During a rainstorm event when positive PWP built up, a remarkably large displacement of 20 mm was recorded between 5.5- and 6-m depths, and the top 5 m of the slope exhibited translational downslope movement. This caused an increase in Bishop’s effective horizontal stress by 350 %, which reached a peak value close to 40 % of a Bishop’s effective passive stress. During the subsequent dry season when suction was recovered, an upslope rebound of 10 mm was recorded. Comparison of field and laboratory data reveals that the rebound was attributed to suction-induced soil shrinkage. This rebound led to a decrease in the Bishop’s effective horizontal stress previously built up during the storm event.     

锦屏一级水电站左岸开挖高边坡变形监测分析

锦屏一级水电站左岸开挖高边坡的开挖高度达到530 m,断层发育,岩体卸荷深度大,地质条件十分复杂,边坡在施工期和运行期的稳定性问题特别重要。对边坡的工程地质条件进行分析,介绍锦屏一级水电站工程左岸边坡的变形监测布置及监测结果。锦屏一级左坝肩边坡采用表面变形观测、浅表变形观测及深部变形观测,由表及里3个层次监测边坡岩体的变形。表面变形监测采用外观变形监测方法;浅部变形监测采用多点位移计,监测深度为0～90 m;深部变形监测采用平洞测距、水准沉降及石墨杆收敛计等监测方法,布置于勘探平洞内,穿越主要断层及深部拉裂缝,最大监测达到260 m。截止2011年5月,边坡浅表最大水平位移106.1 mm,最大垂直下沉位移58.6 mm,主要受边坡开挖及支护控制。深层最大水平变形量为47.48 mm,最大垂直沉降变形为7.2 mm,主要受深部拉裂缝及断层控制。目前位移趋于收敛,最大变形速率小于0.1 mm/d,满足安全控制标准,边坡已趋于稳定。     

Study on collapse settlement and cracks of core wall rockfill dams under wetting deformation

The safety and stability of core wall rockfill dams during impoundment are threatened by the wetting deformation of up-stream shell materials. The serious wetting deformation not only aggravates the collapse settlement of upstream rockfill but also intensifies differential settlement of the dam crest during impoundment, and then causes cracks on the dam crest. On the basis of the proposed wetting deformation model and its simulation method of wetting deformation, this paper simulated the impoundment process of Guanyinyan core wall rockfill dam and studied the deformation characteristic of the dam during impoundment. In addition, the smeared cracking model was used to simulate the crack propagation on the dam crest, and the crack develop and spread mechanism was analysed. The results show that the simulated deformation can fit the in-situ data well, and the simulated crack propagation is in good agreement with the actual situation. Once watered, the upstream rockfill and core wall have significant settlement, and the whole dam crest has obvious horizontal displacement towards the upstream. It is on the same order of magnitude that the increment of horizontal displacement and settlement at the top of the dam during impoundment. In the process of impoundment, the upper part of the dam tends to deform towards the reservoir area, which will lead to tensile cracks appearing in the rockfill areas on both upstream and downstream sides of the core wall of the dam crest, and the propagation direction of the cracks is basically parallel to the adjacent core wall surface. With the water level rising, the cracks on the downstream side of the dam crest mainly extend vertically, and the cracks on the upstream side of the dam crest not only extend vertically, but also extend horizontally.     

巫山县望霞乡桐心村危岩体变形破坏机制分析

本文通过详细调查危岩体所处斜坡变形现象发现,斜坡下部有约1m厚煤层被开采,斜坡上有塌陷和岩体开裂两种变形现象,两种变形均在继续发展;且这两者均与煤层开采有较大关联。工程地质类比法认为采煤引起的沉陷-掀斜变形机制对地表变形起主导作用。采用UDEC数值模拟表明,煤层开采后,位移变形由下向上传递。地表沉陷量向临空面增加,水平位移量也向临空面增加。上部坡体变形受垂直裂隙控制,下部坡体变形受水平层面和煤层控制;整体形成沉陷-掀斜。计算变形曲线显示变形有两个阶段,突破式跳跃变形阶段和缓慢变形阶段;如果没有新的开采活动,随着时间的推移山体最终会自行稳定下来。临空面的孤立危岩体在斜坡系统平衡后仍有较大速率,其稳定性较差,建议对其进行清除。     

Rock Mass Deformation Characteristics in High-Steep Slopes Influenced by Open-Pit to Underground Mining

In Daye Iron Mine, the open-pit mining has ended and the underground mining started in 2003. The present pit slopes are as high as 430 m and the slope angle is up to 43°. During the process of open-pit to underground mining, the high-steep pit slopes would be affected by both open-pit mining and underground mining, and its deformation characteristics would become more complex. So in this paper, the trinity method of numerical simulation, model experiment and field test was adopted to analyze the displacement and stress fields systematically. The results show that: (1) Prominent rebound deformation occurs near the slope foot, which is induced by the unloading in open-pit mining. When it is backfilled to 0 m level, the rebound deformation decreases, which indicate that backfilling mass can restrict the deformation and improve the slope stability; (2) Subsidence dominates the slope deformation in open-pit to underground mining and it increases with an increasing elevation of monitoring point; the maximum horizontal displacement occurs in the lower part of the slopes, because the backfilled part is squeezed by both the north slope and the south slope, and it has a lower elastic modulus than the previous orebody; (3) The stress and its variability near the slope foot are much larger than other places, indicating that the slope foot is most affected by stress redistribution and stress concentration may occur here; the stress at other stress monitoring points changes little, indicating that the influence of open-pit to underground mining is local; (4) The effect of underground mining on the deformation of the faults is not prominent; (5) Mining operations in near-ground part affect more on the variation of deformation and stress of pit slopes than that in deeper part.     

断层带岩体变形模量对坝基稳定性影响

变形模量是表征断层带岩体力学性能的一个重要参数,而断层带岩体变形模量与其所处的环境有密切关系。以理论分析和现场试验为基础,以三维数值分析技术为主要研究手段,结合大型水电工程实例,对断层带岩体变形模量对坝基整体稳定性影响进行了分析研究。研究结果表明：大坝建成水库蓄水以后,在未受到库水渗透影响的前提条件下,位于坝基部位的断层带岩体变形模量会有一定程度的增大。断层带变形模量从0.6 GPa一直增加到4.0 GPa,使得断层带岩体所在坝段关键点水平位移降低0.544~0.846 mm、垂直位移降低1.190~2.232 mm、最大拉应力降低0.06 MPa,有利于提高大坝的整体稳定性。     

宜黄高速公路荆沙公铁立交桥路段变形规律

高路堤侧向滑动、桥台破坏已成为高速公路主要工程病害。荆沙公铁立交桥路段路面与路堤变形严重,对4个变形监测断面、32个地表位移监测点、8个地下水平位移监测孔的数千个观测数据的统计分析表明,该路段在观测期内产生了明显的沉降和水平位移,并具如下规律:路肩以内的填土体自身固结基本完成,由于固结而产生的沉降很小;水平位移较大的监测点处由于水平位移所诱发的沉降较大,并由此产生纵向裂缝;最大变形深度为5m,除局部边坡失稳外,绝大部分路堤趾部基本稳定,路堤的变形仅限于其内部;边坡上各监测点的变形远远大于路肩、趾部,边坡下部又较上部显著,说明路堤变形主要危险在于边坡的侧向变形,而边坡则通过滑塌调整其稳定性。     

Stress and Deformation Analysis of Concrete-Facing Sand–Gravel Dam Based on Inversion Parameters

With the long-term operation of the project, the material parameters of concrete-facing sand–gravel dam will change, which brings great difficulty to the scientific and effective stress and deformation analysis. Combining with the measured displacement data, the finite element analysis model of the concrete-facing sand–gravel dam of Heiquan reservoir was established, and the modulus of elasticity and internal friction angle of the dam body were inverted by the measured displacement of the dam, then the simulation analysis of the filling construction process and the reservoir storage process of dam was carried out, and the stress and deformation values of the dam during the construction period and the impoundment period were calculated. The results showed that the parameters obtained from the inversion are smaller than the original parameters, but there is little difference between them. The displacement calculated by finite element inversion was close to the measured displacement value, the overall displacement and stress distribution of the dam body and panel were in line with the general law, and the calculated displacement and stress values were at the normal level. This study provides a reference for parameter inversion and stress and deformation analysis of concrete slab dam through monitoring data analysis.

     

常州润华环球中心深基坑支护效果分析

常州润华环球中心基坑工程一区开挖深度达18 m,采用钻孔灌注排桩和内支撑作为支护结构。基坑施工过程中对基坑顶部的沉降位移和水平位移进行了监测。基坑工程施工结束后基坑顶部的沉降位移和水平位移达到稳定值（分别为25 mm和40 mm）,整体支护效果显著。但在基坑第三次开挖结束后第二道支撑构筑完成之前,基坑顶部的沉降位移和水平位移速率突然增大,直至第二道支撑构筑完成后增速才缓慢降低。提高第二道支撑的标高有利于降低基坑的变形,提高支护效果。     

云南成品油管道安宁高填方边坡变形规律研究

随着中国西南部山区基础设施建设的迅猛发展,机场、高速公路和铁路等建设项目高填方地基日益增多,建设期间填方区域的大变形及其工后阶段的长期缓慢变形直接影响到建设场地的正常使用,特别是存在边坡临空面的填方工程,填方土体的坡度、水平向变形关系到坡体的整体稳定性。本文以云南安宁市一高填方边坡为例,通过现场勘察及对填方过程中监测数据的分析,应用数值模拟软件对填方坡体的变形特征进行研究。研究结果表明,坡体总变形以沉降为主,最大值出现在坡体内部,大部分变形发生在施工过程中,工后沉降很小,坡体垂直位移最大值出现在填筑体与原地基土交界面处,沉降等值线闭合呈椭圆状;坡体水平位移最大值出现在原地基土内,水平位移等值线图整体呈条带状由坡底斜向延伸至罐区东侧,水平位移变化较大区域与实际地表裂缝位置一致。研究成果对存在边坡临空面的填方工程施工过程及工后变形量预测控制、坡体上部裂缝病害研究具有一定的参考价值和指导意义。     

某水电站左岸深裂缝对工程荷载下边坡稳定性影响的FLAC3D分析

简要介绍了某水电站下坝址区左岸深部裂缝的发育分布特征，在此基础上，采用FLAC^3D就深裂缝的存在对工程荷载作用下坝基岩体的变形和稳定性状况进行了初步分析和评价，结果表明，尽管左岸边坡中存在深裂缝，但岸坡在工程荷载作用下变形较小，整体稳定性仍较好。     

Understanding the triggering mechanism and possible kinematic evolution of a reactivated landslide in the Three Gorges Reservoir

More than 5000 landslides or potential landslides have been induced in the Three Gorges Reservoir (TGR) region since the impoundment in 2003, which have caused great damage and remain a huge threat to the dam and people living in the reservoir area. Understanding the deformation characteristics and failure mechanism of the landslides can be helpful in stability evaluation and landslide prediction. The primary aim of this study is to research the characteristics of the landslide motion and its relationships with environmental triggers, taking the Quchi landslide, a large, slow-moving, reactivated landslide in the TGR region, as an example. The instability clearly showed visible signs of movements since 2002, and after that, the slope has been experiencing persistent deformation. By combining 4 years of meteorological, hydrological data with displacement measurements from open fractures, deep boreholes, and surface points, as well as in situ observations, this paper reports the geological and geotechnical investigations performed to define the movement. The deformation is believed to be governed by reservoir water levels, while the precipitation has a minor effect. Seasonally, the slope movement has a very distinctive pattern with large deformation starting abruptly right after reservoir drawdown in June and lasting into late summer (September). Then there is a rapid transition to constant deformation (almost no displacement) as the reservoir level rises. The slope displacements appear to gradually increase every year, which suggests very high possibility of the large and overall failure of the slide. Both monitoring results and geomorphological observations have highlighted that the two active slide masses Q1 and Q2 would probably collapse in different kinematic evolution modes, i.e., the multistage failure and whole sliding motion.     

Validity evaluation of a groundwater dam in Oshipcheon River,eastern Korea using a SWAT–MODFLOW model

It is assumed that the groundwater dam under consideration is located in the lower Oshipcheon River along Yeongdeok-gun County, Gyeongsangbuk-do Province, eastern Korea. In this study, changes in groundwater level and construction effects of the groundwater dam were analyzed using a SWAT–MODFLOW model designed for integration of surface water and groundwater, and validity analysis before and after construction of the groundwater dam was evaluated. There are an average increase of 0.46 m and a maximum increase of 1.16 m, respectively, at the upstream region due to the groundwater dam. Groundwater levels at the upstream region show an average increase of 0.42 m by the groundwater dam when the water quantity of demand (10,080 m³/day) is pumped. The groundwater dam has potential as an alternative for the surface water dam to secure water resources in the study area.     

Monitoring and early warning of the 2012 Preonzo catastrophic rockslope failure

In this paper, we describe the investigations and actions taken to reduce risk and prevent casualties from a catastrophic 210,000 m³ rockslope failure, which occurred near the village of Preonzo in the Swiss Alps on May 15, 2012. We describe the geological predisposition and displacement history before and during the accelerated creep stage as well as the development and operation of an efficient early warning system. The failure of May 15, 2012, occurred from a large and retrogressive instability in gneisses and amphibolites with a total volume of about 350,000 m³, which formed an alpine meadow 1250 m above the valley floor. About 140,000 m³ of unstable rock mass remained in place and might collapse partially or completely in the future. The instability showed clearly visible signs of movements along a tension crack since 1989 and accelerated creep with significant hydromechanical forcing since about 2006. Because the active rockslide at Preonzo threatened a large industrial facility and important transport routes located directly at the toe of the slope, an early warning system was installed in 2010. The thresholds for prealarm, general public alarm, and evacuation were derived from crack meter and total station monitoring data covering a period of about 10 years, supplemented with information from past failure events with similar predisposition. These thresholds were successfully applied to evacuate the industrial facility and to close important roads a few days before the catastrophic slope failure of May 15, 2012. The rock slope failure occurred in two events, exposing a compound rupture plane dipping 42° and generating deposits in the midslope portion with a travel angle of 39°. Three hours after the second rockslide, the fresh deposits became reactivated in a devastating debris avalanche that reached the foot of the slope but did not destroy any infrastructure. The final run-out distance of this combined rock collapse–debris avalanche corresponded to the predictions made in the year 2004.     

尾矿坝垮塌机制与溃决模式试验研究

基于云南拉拉铜矿小打鹅尾矿库工程设计资料,采用现场排放尾矿砂为试验材料,进行了尾矿堆积坝在洪水情况下发生垮塌破坏的模型试验。通过水流控制系统模拟尾矿坝遭遇洪水情况,采用侧面示踪点、水位测压管、应力传感器以及数码摄像机等设备获得了尾矿坝溃决过程中坝坡的位移矢量演化、浸润线与应力的变化特性以及坝体破坏发展过程,揭示了洪水作用下尾矿坝的垮塌机制和溃决模式。试验结果发现：尾矿堆积坝的浸润线变化存在滞后性;在洪水入库致库区最高设计洪水水位过程中,靠近坝坡中部处水平方向的总应力增量较垂向总应力增量大,增大的水平应力是坝体产生破坏的重要因素之一;洪水导致坝坡尾矿砂所受的渗透力、上浮力、重力以及孔隙水压力增大,削弱了坝体材料的黏聚力,并加大了自身荷载,降低了坝体的稳定性;尾矿坝溃决模式一般为逆流渐进型,破坏先是从坡脚处发生,继而向上游发展,呈现牵引式发展,破坏的滑动面由多个弧形滑移面构成。研究成果加深了对尾矿堆积坝垮塌机制和溃决模式的认识,并在洪水灾害的预防和控制方面作了一些新的探索     

三峡库区顺层灰岩岸坡劣化−溃屈灾变机制研究

三峡库区巫峡段发现多处顺层岸坡滑移−弯曲变形迹象,库水循环涨落加剧了岸坡前缘劣化损伤与失稳破坏。以巫峡段青石 6号坡为例构建室内概化模型,开展顺层灰岩岸坡在消落带岩体劣化下的灾变机制研究。研究结果表明：蓄水前岸坡整体长期处于稳定状态。随着劣化进行,蓄水后岸坡变形加剧直至溃屈破坏,岩体劣化缩短了劣化−溃屈失稳进程。运动学分析显示,溃屈破坏时同一岩层达到速度峰值近似。岩层“弯折点”后部运动特征较为一致,前部较为离散。溃屈破坏点是岸坡能量释放的转折点和顶点;随劣化演变位移、应力逐渐递增,呈现提前破坏征兆,溃屈破坏前后应力产生“集中−释放”。整体来看,应力变化提前于位移,表明应力监测更有效。应力监测的核心在于关键区段的确定,对于劣化−溃屈型岸坡来讲,前缘“挠曲段”处应力陡增可作为岸坡临界失稳的重要表征;“劣化−溃屈”演化进程中后缘推挤始终存在,它是岸坡灾变的前提。但岸坡失稳的主导因素却是消落带岩体持续不断的劣化。青石 6 号坡当前处于向强烈弯曲隆起演化进程中,由于消落带岩体持续劣化,可能由稳定/基本稳定逐渐演变为欠稳定状态。