地震作用下尾矿坝变形及稳定性时程分析

采用永久变形分析和地震时程分析相结合的综合研究方法,开展某大型现场尾矿坝的稳定性评价。依据尾矿坝工程场地地震安全性评价结果,确定工程场地50a超越概率10%、5%的荷载时程输入曲线;采用修正UBCSAND模型进行隐式非线性分析;采用粘性输入边界,解决动力荷载时程较长时引起计算不收敛的问题;进行尾矿坝的三阶振型特征周期计算;进行基本烈度下永久变形分析,剖析不同坝体标高的变形特征;绘制位移云图并剖析位移变化特征;采用时程+SRM法,计算绘制50a超越概率10%和5%的安全系数时程曲线。根据永久变形和稳定性系数计算结果,综合判定尾矿坝稳定状态,据此对现场尾矿坝提出加固建议。建立的研究方法和成果可为大型尾矿坝稳定性评价工程提供参考。     

考虑土性空间变异的尾矿坝失稳概率分析

本文依托马鞍坪小打鹅尾矿库扩容工程项目,考虑尾矿坝内土性的空间变异,运用Monte-Carlo和敏感性分析的方法,得到了洪水工况下该尾矿坝的失稳概率、可靠性指标和敏感性曲线,并讨论了概率方法在工程上运用的优势。这些研究成果,对现场尾矿库安全施工与管理具有一定指导意义。     

铁矿尾矿料力学特性及坝体变形稳定性研究

尾矿料矿物成分复杂,物理力学特性区域差异性大。本文以西南地区某铁矿拟建尾矿库为研究对象,对粗、细两种尾矿料进行了系统的物理力学特性试验,获得了粗细尾矿料物理力学指标并应用到尾矿库坝数值分析,分析了该尾矿库坝的应力变形特性,对不同堆积高程、不同工况下尾矿库坝的安全稳定性进行计算分析。此外采用拟静力法对地震荷载作用下尾矿坝的稳定性进行分析。结果表明,粗尾矿料会呈现出剪胀和软化力学特性,而细尾矿料则无明显剪胀;尾矿坝坝体内以压应力为主,坝体表面出现小范围拉应力区;高堆积高程,坝体倾向于发生深层滑动,坝体最小安全稳定性系数较大;干滩长度增大明显提高坝体稳定性;最后对该尾矿库的安全运行提出了一些针对性措施及建议。     

基于流固耦合理论某尾矿坝失稳特性及稳定性分析

选用典型的尾矿库工程实例,采用流固耦合和强度折减法相结合对其尾矿坝进行稳定性分析,确定尾矿库渗流场分布及浸润线的位置,该浸润线位置与实测浸润线位置吻合较好。建议强度折减过程中尾矿坝的失稳准则,计算安全系数,确定潜在滑裂面的位置,并与极限平衡法计算出的安全系数及临界滑裂面位置进行比较,表明强度折减法得出的结果与Bishop法结果接近,流固耦合-强度折减法在尾矿库稳定性分析的可行性。在该基础上研究尾矿坝潜在的失稳模式,将尾矿坝潜在的失稳模式分为局部失稳和整体性失稳两种,局部失稳为尾矿坝的部分坝面发生滑移,整体失稳为整个尾矿坝坝体发生失稳,并分析导致该尾矿坝两种失稳模式的主要因素,认为浸润线埋深过浅是导致局部失稳的主要原因。     

四川会东老虎岩尾矿坝地震反应分析

应用有效应力有限元法研究了老虎岩尾矿坝在不同坝高时的应力水平、变形和孔隙水压力分布,以及遭到Ⅶ度地震作用时的反应.分析结果表明:在当前坝高情况下,无地震作用时尾矿坝处于稳定状态.在受烈度为Ⅶ度的地震作用下,尾矿堆积坝坝外坡和沉积滩面的堆积尾矿砂土在局部已经发生液化破坏;在封库坝高情况下,无地震作用时尾矿坝处于极限状态.在受烈度为Ⅶ度的地震作用下,尾矿坝坝外坡和沉积滩面的堆积尾矿砂土已发生大面积液化破坏.在地震作用下,老虎岩尾矿坝堆积尾矿产生液化破坏的主要原因是堆积坝体内浸润线的埋深较浅.对老虎岩尾矿坝必须加强排渗措施,使坝体内浸润线下移.     

土石坝拟静力抗震稳定性分析与坝坡地震滑移量估算

单独采用拟静力抗震稳定性安全系数,并不能准确地评价土石坝的动力稳定性, Newmark等采用刚塑体滑移量或永久变形评价土石坝地震稳定性的建议得到了逐步认同,但土石坝地震永久变形或滑移量的估算尚缺乏合理方法。为此,将土石坝地震动力响应分析和拟静力极限平衡分析相结合,提出了合理地估算坝坡上潜在滑坡体地震滑移量的数值计算方法。首先,根据土石坝地震动力响应分析,针对圆弧滑动面和非圆弧光滑渐变曲面形式滑动面,分别采用简化Bishop法及改进的简化Bishop法计算坝坡上潜在滑动体的各个时刻拟静力安全系数。随后,对其中安全系数小于1的瞬时超载阶段,通过时间积分确定潜在滑动体的滑移量。最后,结合算例并通过具体数值计算与分析探讨了竖向地震动分量、滑坡体竖向地震响应、振动孔隙水压力等各种因素对土石坝地震位移及抗震性能的影响。     

高浓缩分级尾矿上游法堆坝及模型试验研究

针对传统上游法尾矿库堆坝方法的缺陷与不足,提出了改进的上游法堆坝方法,即高浓缩分级尾矿上游法堆坝方法。基于尾矿库堆坝模型试验,以高浓缩尾矿堆存技术为指导,分别进行传统上游法和改进上游法的高浓缩尾矿堆坝模型试验,演绎尾矿库堆坝过程,测试并得出了堆坝过程中滩面尾矿沉积情况、尾矿颗粒分布规律及浸润线变化规律,并采用极限平衡法计算不同堆坝方式下坝体的最小安全系数。结果显示：高浓缩尾矿堆坝使沉积滩颗粒分布均匀,颗粒分级不明显,减少了互层和细泥夹层的出现,改善了坝体内部结构;改进上游法堆坝可以形成有利于排渗防洪的良好沉积滩滩型;稳定性分析结果表明,改进上游法堆坝方法可以使尾矿坝的稳定性提高19%～33%,研究成果可为新建尾矿库工程提供试验技术支撑。     

金堆城尾矿坝加高方案数值模拟及稳定性分析

金堆城尾矿坝为了进行加高设计而对尾矿库区进行了地质钻孔勘探。基于实际钻孔勘探成果,最佳反演分析了各分区-尾矿砂和初期坝堆石体模型的渗透系数、物理力学指标和加高方案下的浸润面分布。结合加高设计方案,采用基于有效应力法的EFES-3D计算程序对该尾矿坝加高后的应力应变场进行了数值模拟和坝坡稳定性分析,得出应力应变场分布图和边坡安全系数。可以看出,在上游法加高方案下,尾矿坝坝坡有涌起抬高现象,安全系数有所降低,不利于尾矿坝的稳定安全和运行管理。为此提出了在加高方案设计中加强排渗设施建议。     

基于动力离心试验的软基尾矿库地震响应研究

基于离心机振动台,分别针对典型软基尾黏土尾矿库及加高扩容后的尾矿库开展了动力离心模型试验,重点探究了加速度分布规律、软土及尾矿内部孔压变化规律以及“软基?库内尾矿?尾矿坝”系统的变形规律等内容。试验结果表明：软基对地震动的放大效应较为微弱,而坝体加速度沿高程逐渐放大,高层子坝加速度响应最为强烈,加高扩容后的现坝顶加速度响应可达原坝顶的2.2倍;地震作用下软土与库内尾矿内部均会产生一定的孔压增量,但未达到液化状态。地震动强度、软基及库内尾矿的固结状态对尾矿库的变形模式影响较大。当固结不充分时,在强震作用下易发生尾矿的水平滑移,进而造成坝顶及下游软土隆起。在固结较为充分且地震动强度较弱的情况下,变形模式以震陷为主。该试验成果将为此类尾矿库的动力稳定分析及抗震加固设计提供一定参考。     

水平向与竖向地震动的时间遇合模式对边坡动力安全系数的影响

通过沿滑面的应力积分法和动力时程分析法,研究了水平向、竖向地震动单独作用对边坡动安全系数的影响,发现竖向地震动与水平向地震动一样也对边坡抗震稳定性有显著的影响。在此基础之上,重点探讨了实际地震的双向地震动同时作用时,其时间遇合模式对动力安全系数的影响,结果表明,常用的加速度峰值遇合模式和随机遇合模式都不能充分体现出竖向地震动与水平向地震动的叠加效应,进而造成对安全系数的高估;文中提出的最大地震作用效应遇合模式才是最危险的遇合模式,其所得稳定性安全系数时程的极值更小。在考虑多向地震的边坡抗震分析中,由于多维地震动的强烈随机性,应考虑出现这种最大地震作用效应遇合的可能性,以得到工程设计中偏于安全的动力稳定性安全系数值。     

A study on geotechnical characterization and stability of downstream slope of a tailings dam to improve its storage capacity (Turkey)

Tailings, waste products of the ore-dressing processes, are usually stored in a slurry form and pumped into sedimentation pond which is surrounded by natural heights and/or artificial walls. The database of International Commission of Large Dams and United Nations Environment Programme showed that several hundreds of tailings dam have failed since 1910. One of the reasons of these failures is slope instability. Construction of mine tailings dams in Turkey has started to increase, particularly in the recent decade. This paper focuses the study undertaken to assess the geotechnical characteristics and stability of downstream slope of a tailings dam at a copper-zinc mine in the Black Sea Region of Turkey. At the mine site there are two tailings dams located at two different elevations. The upper dam was completely filled and is out of service. Increasing amount of tailings filling the pond of the lower dam resulted in a limited storage, and therefore, it has been decided that heightening of the dam about 7 m to improve its storage facility would be necessary. For the purpose, a series of investigations in the vicinity of the tailings dam and some geomechanical laboratory tests were carried in conjunction with the use of empirical methods to determine mechanical properties of the current dam material, tailings and the rockfill material that will be used for heightening of the dam. The results of the static and pseudo-static stability analyses based on the methods of limit equilibrium and numerical modelling indicated that circular and non-circular failures are the most critical modes of failure for the dam and safety factor gradually decreases when the tailings rise up to a specific elevation in the pond. However, the ranges of the calculated safety factors from both methods are considerably similar and suitable for heightening of the dam by 7 m in terms of stability. The results suggest that any instability is not expected under both static and dynamic conditions after the current height of the tailings dam is increased by 7 m, if the slope geometry considered in the analyses is not changed and the tailings in the pond do not rise up to an elevation of about 475 m. In addition, magnitude of permanent settlement of the dam due to a probable earthquake was also assessed using two empirical methods and the results from both methods showed similar amount of settlements which were in tolerable limits.     

Dynamic characteristics of tailings reservoir under seismic load

Earthquake is one of the most important factors that leads to the liquefaction of tailings and to the instability of the tailings reservoir. Therefore, it is of great practical significance to study the instability mechanism of the tailings reservoir under seismic load. In this study, the dynamic characteristics of the tailings reservoir under seismic load were investigated by carrying out a model test on the dynamic characteristics of the tailings dam. A model test of tailings dam failure and the dynamic characteristics model of the tailings reservoir under seismic load were established. Additionally, the dynamic characteristics under a seismic load were investigated. Additionally, the correctness of the dynamic characteristics model of the tailings reservoir was verified by numerical calculation. Researches show that with the increase in input peak acceleration, pore water pressure, earth pressure, and the horizontal and vertical displacements of the dam monitoring points are gradually increased. However, the acceleration amplification factor shows a declining trend. In the process of increasing the input peak acceleration, the saturation line and the lifting speed increases gradually. There is no obvious slip surface in the failure of the tailings dam, and the overall sliding is shown by the failure mode. The tailings reach each of the downstream sections. The mud height increases to the peak value, and then decreases gradually until stagnation. The results of this study can provide the theoretical basis and reference values for the stability analysis of a tailings reservoir under a seismic load, and the results are of great significance for controlling the risk factors in the operation of tailings reservoir, reducing the risk of tailings production safety, preventing the occurrence of tailing pond accidents, protecting the property safety of the downstream residents and enterprises, maintaining social stability around the reservoir area and creating a good ecological environment.     

基于有限元极限平衡法的尾矿坝坝体稳定分析

在平面应变条件下,采用基于弹塑性应力应变分析的有限元极限平衡法对尾矿坝坝体的稳定性进行研究。该方法可较好地结合极限平衡分析方法和有限元应力分析方法的特点。通过弹塑性有限元分析,合理准确地考虑结构整体应力场的影响,进而结合Hooke-Jeeves法优化搜索最危险滑动面的位置及其对应的最小安全系数。以某尾矿坝实际工程为例,比较分析了考虑正常、洪水以及特殊工况运行下有限元极限平衡法与极限平衡条分法和有限元强度折减法在安全系数大小及滑动面形状和位置的差异,重点运用有限元极限平衡法对尾矿坝坝体的稳定性进行验算并作出安全评价,为尾矿坝的安全设计施工提供可靠依据和技术支撑。     

The effect of reservoir length on seismic performance of gravity dams to near- and far-fault ground motions

In this article, the effect of reservoir length on seismic performance of gravity dams to near- and far-fault ground motions is investigated. For this purpose, four finite element models of dam–reservoir–foundation interaction system are prepared by using the Lagrangian approach. In these models, the reservoir length varies from H to 4H (H: the height of dam). The Folsom gravity dam is selected as a numerical application. Two different ground motion records of 1989 Loma Prieta earthquake are used in the analyses. One of ground motions is recorded in near fault; the other is recorded in far fault. Also, the two records have the same peak ground acceleration. The study mainly consists of three parts to assess the effects of reservoir length on the seismic performance of the concrete gravity dam. In the first part, the linear time-history analyses of the four finite element models prepared for the Folsom gravity dam are performed. In the second part, the seismic performance of the dam is evaluated according to demand–capacity ratio and cumulative inelastic duration. Finally, the nonlinear time-history analyses of the finite element models of the dam are carried out by using Drucker–Prager yield criteria for dam concrete. It is seen from the analyses results that the seismic behavior of the concrete gravity dams is considerably affected from the length of the reservoir. The reservoir length of 3H is adequate for concrete gravity dams. The selection of ground motion is on of the important parts of seismic evaluation of gravity dams. Also, the frequency characteristics of the ground motion having the same peak ground acceleration affect the seismic performance of the dam. The near-fault ground motions are generally creates more stress on the dam body than far-fault ground motions. The used performance approach provides a systematic methodology for assessment of the seismic performance and necessity of nonlinear analyses for dam systems.     

尾矿库边坡时变分析模型及其应用

尾矿库边坡稳定性多以单一安全系数为评价指标,难以反映外界条件变化的过程中尾矿库边坡稳定性演化的全过程特征。针对这一问题,提出尾矿库稳定性的时变分析方法,以安全系数时程曲线分析尾矿库边坡稳定性。以尾矿库工程实例为研究对象,建立时变分析模型进行数值模拟。研究在不同降雨入渗、库水位变动以及二者耦合条件下边坡安全系数随时间变化的规律。研究结果表明,不同强度的均匀降雨影响下,6 h以后安全系数下降速率大致相当,6 h以内雨强越大,安全系数下降越快。降雨雨型将影响安全系数变化轨迹,研究较为广泛的均匀雨型并不是最危险雨型。边坡安全系数变化滞后于库水位变动,滞后效应随水位上涨速度的减慢、下降速度的加快和涨幅的减少而减弱。耦合条件下尾矿库边坡安全系数减小将加剧。研究成果对尾矿库设计和运营具有重要意义。