Probabilistic seismic stability of three-dimensional slopes by pseudo-dynamic approach

Probabilistic analysis is a rational approach for engineering design because it provides more insight than traditional deterministic analysis. Probabilistic evaluation on seismic stability of three dimensional (3D) slopes is studied in this paper. The slope safety factor is computed by combining the kinematic approach of limit analysis using a three-dimensional rotational failure mechanism with the pseudo-dynamic approach. The variability of input parameters, including six pseudo-dynamic parameters and two soil shear strength parameters, are taken into account by means of Monte-Carlo Simulations (MCS) method. The influences of pseudo-dynamic input variables on the computed failure probabilities are investigated and discussed. It is shown that the obtained failure probabilities increase with the pseudo-dynamic input variables and the pseudo-dynamic approach gives more conservative failure probability estimates compared with the pseudo-static approach.

Analytical expressions for determining the stability of cohesionless soil slope under generalized seismic conditions

In recent major earthquakes, the researchers have found the need for consideration of vertical seismic acceleration for the stability analysis of the man-made and natural slopes. However, in most past studies, the performance of slopes has been assessed by accounting only the horizontal seismic component of the ground motion, without giving due weightage to the effect of vertical component. In the present study, analytical expressions are derived to determine the factor of safety, yield seismic coefficient and consequently the seismic displacement of cohesionless soil slope under combined horizontal and vertical components of the ground motion. The derivation uses the Newmark's sliding block approach, in which the soil slope with a planar failure surface within the framework of conventional pseudo-static analysis is assumed to follow the Mohr-Coulomb failure criterion. The effects of vertical seismic coefficient on the stability of cohesionless slope have been studied through a set of graphical presentations for a specific range of soil parameters. It is observed that overlooking the effect of the vertical component of the ground motion on factor of safety and the displacement while designing the slope may be detrimental, resulting in the slope failure. The general expressions presented in this paper may be highly useful in the field of earthquake geotechnical engineering practice for designing the cohesionless soil slopes under combined horizontal and vertical seismic loads.

Efficiency of scalar and vector intensity measures for seismic slope displacements

Ground motion intensity measures are usually used to predict the earthquake-induced displacements in earth dams,soil slopes and soil structures.In this study,the efficiency of various single ground motion intensity measures(scalar IMs)or a combination of them(vector IMs)are investigated using the PEER-NGA strong motion database and an equivalent-linear sliding-mass model.Although no single intensity measure is efficient enough for all slope conditions,the spectral acceleration at 1.5 times of the initial slope period and Arias intensity of the input motion are found to be the most efficient scalar IMs for flexible slopes and stiff slopes respectively.Vector IMs can incorporate different characteristics of the ground motion and thus significantly improve the efficiency over a wide range of slope conditions.Among various vector IMs considered,the spectral accelerations at multiple spectral periods achieve high efficiency for a wide range of slope conditions.This study provides usefiul guidance to the development of more efficient empirical prediction models as well as the ground motion selection criteria for time domain analysis of seismic slope displacements.

Applying real time seismic monitoring technology for slope stability assessment—An Indian opencast coal mine perspective

This paper outlines the results obtained from real time microseismic monitoring of an opencast coal mine in South India.The objective of the study is to investigate the stress changes within the rockmass along the slope due to underground mine development operation and their impact on the stability of the highwall slope.The installed microseismic systems recorded the seismic triggerings down toà2 moment magnitude.In general,most of the events recorded during the monitoring period are weak in seismic energy.The study adopts a simple and more reliable tool to characterize the seismically active zone for assessing the stability of the highwall in real time.The impact of underground working on the slope is studied on the basis of the seismic event impact contours and seismic clusters.During the monitoring period,it is observed that the intensity of the overall microseismic activity along the slope due to the mine development operations did not cause any adverse impact on the highwall stability.

Seismic stability evaluation of embankment slope based on catastrophe theory

An evaluation method for the seismic stability of embankment slope was presented based on catastrophe theory. Seven control factors, including internal frictional angle, cohesion force, slope height, slope angle, surface gradients, peak acceleration, and distance to fault were selected for analysis of multi-level objective decomposition. According to the normalization formula and the fuzzy subject function produced by combination of catastrophe theory and fuzzy math, a recursive calculation was carried out to obtain a catastrophic affiliated functional value, which can be used to evaluate the seismic stability of embankment slope. Fifteen samples were used to verify the effectiveness of this method. The results show that compared with the traditional quantitative method, the catastrophe progression owns higher accuracy and good application potential in predicting the seismic stability of embankment slope.

Seismic stability of jointed rock slopes under obliquely incident earthquake waves

Seismic stability of slopes has been traditionally analyzed with vertically propagated earthquake waves.However,for rock slopes,the earthquake waves might approach the outcrop still with a evidently oblique direction.To investigate the impact of obliquely incident earthquake excitations,the input method for SV and P waves with arbitrary incident angles is conducted,respectively,by adopting the equivalent nodal force method together with a viscous-spring boundary.Then,the input method is introduced within the framework of ABAQUS software and verified by a numerical example.Both SV and P waves input are considered herein for a 2 D jointed rock slope.For the jointed rock mass,the jointed material model in ABAQUS software is employed to simulate its behavior as a continuum.Results of the study show that the earthquake incident angles have significance on the seismic stability of jointed rock slopes.The larger the incident angle,the greater the risk of slope instability.Furthermore,the stability of the jointed rock slopes also is affected by wave types of earthquakes heavily.P waves induce weaker responses and SV waves are shown to be more critical.

Effects of vertical seismic acceleration on 3D slope stability

The conventional pseudo-static approach often neglects the effect of the vertical＇ seismic acceleration on the stability of a slope, but some analyses under plane-strain （2D） conditions show a significant effect on the slope stability. The purpose of this study is to investigate the effect of the vertical acceleration on the safety of three-dimensional （3D） slopes. In the strict framework of limit analysis, a 3D kinematically admissible rotational failure mechanism is adopted here for 3D homogeneous slopes in frictional/cohesive soils. A set of stability charts is presented in a wide range of parameters for 3D slopes under combined horizontal and vertical seismic loading conditions. Accounting for the effects of the vertical seismic acceleration, the difference in safety factors for 3D slopes can exceed 10%, which will significantly overestimate the safety of the 3D slopes.

Numerical simulation of roadbed slope under seismic action in permafrost regions

The deformation and strength characteristics of roadbed slope under seismic loading in permafrost regions are simulated numerically. The seismic response of roadbed at different positions and inclinations of a slope section was analyzed. Results show that, roadbed slope damage is mainly led by lateral displacement, and the deformation gradually decreases with increasing depth; roadbed and foundation displacement and plastic strain increases with the magnitude of slope angle, hence the roadbed safety factor will be reduced.

Slope stability analysis under seismic load by vector sum analysis method

The vibration characteristics and dynamic responses of rock and soil under seismic load can be estimated with dynamic finite element method （DFEM）. Combining with the DFEM, the vector sum analysis method （VSAM） is employed in seismic stability analysis of a slope in this paper. Different from other conventional methods, the VSAM is proposed based on the vector characteristic of force and current stress state of the slope. The dynamic stress state of the slope at any moment under seismic load can he obtained by the DFEM, thus the factor of safety of the slope at any moment during earthquake can be easily obtained with the VSAM in consideration of the DFEM. Then, the global stability of the slope can be estimated on the basis of time-history curve of factor of safety and reliability theory. The VSAM is applied to a homogeneous slope under seismic load. The factor of safety of the slope is 1.30 under gravity only and the dynamic factor of safety under seismic load is 1.21. The calculating results show that the dynamic characteristics and stability state of the slope with input ground motion can be actually analyzed. It is believed that the VSAM is a feasible and practical approach to estimate the dynamic stability of slopes under seismic load.

高震区斜坡式护岸的岸坡稳定性分析

对位于菲律宾高震区的某斜坡式护岸结构的岸坡进行稳定性评估,分析国际上主流抗震设计规范,结合该工程的具体设计条件,提出合适的地震岸坡稳定分析方法、稳定标准和分析流程,并采用Newmark法和非线性动力分析对该护岸的震后残余位移进行计算。结果表明:高震区的岸坡稳定分析宜以控制位移为目标,水准1、2地震下的残余位移宜分别不超过5、30 cm;当采用Newmark法计算时宜取其上限位移,而通过非线性动力分析可获得岸坡残余位移和最大剪应变等的分布,从而对地震下的岸坡稳定做更为全面的设计和评估。

地震荷载下边坡大变形失稳破坏形式研究

采用物质点法分析边坡失稳破坏模式,通过改变土体参数,确定浅层、中层与深层破坏形式边坡模型,进而分析在考虑土体应变软化模型及不同地震荷载作用下,三种边坡破坏模式的破坏过程和变化规律.研究表明,在静态计算中考虑应变软化时,边坡破坏过程较为复杂,滑体沿着滑面整体滑移后,浅层破坏滑体会持续破坏成碎散块体,中层破坏滑体持续分裂成小块体,深层破坏滑体出现新的层状失效区.动态计算中不考虑应变软化时,地震荷载不改变边坡的破坏形式,但加剧边坡的滑移和变形,且随着地震荷载峰值加速度的增加而增加.在考虑应变软化时,地震荷载峰值加速度的增加会改变边坡破坏形式,摩擦角在这个过程中起着重要作用.研究结果可为边坡治理、预防滑坡提供参考.

地震放大作用下裂缝边坡稳定性极限分析及影响规律研究

大量试验数据和震后调查表明,地震加速度沿坡高具有显著放大效应并导致产生坡顶裂缝。为探究放大效应对边坡稳定性和坡顶裂缝的影响,基于极限分析上限法和拟静力法,建立考虑放大效应的裂缝边坡稳定性分析方法,得到地震放大作用对边坡稳定性和裂缝开展情况的影响规律。计算结果表明:裂缝边坡安全系数随地震放大系数增加而降低,陡坡和缓坡在考虑地震放大效应后安全系数均下降约10%,坡顶裂缝随地震放大系数增大逐渐远离坡肩,但裂缝深度会减小,其中当坡底地震加速度较大时放大效应对裂缝位置和深度影响显著。根据地震裂缝边坡安全系数的上限解c/γHtanφ与边坡参数F/tanφ值呈现幂函数的特征,通过拟合获得了安全系数计算表达式,可在实际工程中快速评估地震放大效应对裂缝边坡安全系数的影响。

某钨矿露地联采关键地压灾害监测预警研究

某钨矿形成了露地联采的开采局面,面临着井下群采空区与隔离间柱稳定性、露采边坡稳定性、露地相互影响等关键地压灾害问题。设计建设了最先进的66通道微震监测系统、测量机器人与边坡雷达等地压监测预警系统。文章详细介绍了一次典型的岩体失稳垮塌的成功预警案例。上述综合性的地压监测手段将为矿山安全生产提供重要的技术支撑。

地震荷载下预应力锚固边坡离心振动模型试验研究

预应力锚索作为边坡支护的重要技术,已经在边坡加固中得到了广泛应用,但锚固岩质边坡在地震荷载作用下的响应机制以及锚索受力变形规律还不明确。为此,开展了预应力锚固边坡离心振动模型试验,系统介绍了模型相似设计、模型设计与制作、地震荷载施加等试验关键技术,并以紫坪铺水库泄洪洞进口岩质边坡为原型,开展了简谐地震波作用下的锚固边坡离心模型试验。对试验结果进行了分析,并对该离心振动试验的主要影响因素进行了探讨。研究结果表明:地震作用下预应力锚索发挥了较强的被动支护作用,且越靠近滑面处应力应变响应越明显;边坡竖向位移与应力应变值的响应情况随地震烈度的改变产生明显变化。研究成果可为今后离心振动模型试验的开展提供参考与借鉴。

地震动力响应下某矿山排土场边坡稳定性分析

地震引起的边坡动力响应是诱发排土场失稳的主要诱因之一。以某矿山排土场边坡为背景,采用Geostudio软件模拟分析了Ⅷ级地震作用下某排土场边坡质点位移时程曲线、质点应变时程曲线以及安全系数时程变化曲线。研究结果表明:在地震力作用时间段内,该矿山排土场边坡最大质点位移、最大质点应变仅为8 cm与0.002 5,安全系数最小值为1.65,大于规定的许用安全系数1.10,表明该排土场边坡处于稳定状态。

爆破振动作用下含断层边坡动力响应分析

依据施加爆破地震波后含断层边坡稳定性模拟计算结果,研究了爆破振动作用下不同断层厚度边坡的动力响应变化规律。结果表明,爆破地震波在边坡坡表及断层区域传播时存在高程放大效应;断层厚度越大,爆破地震波衰减越快;随着断层厚度增加,边坡在爆破振动作用下产生的位移逐渐增大,整体抵抗变形能力变小;爆破振动作用下不同断层厚度对边坡稳定性影响差异明显,断层厚度2~8 m时边坡稳定性呈持续快速降低趋势,断层厚度超过8 m后边坡稳定性趋于平稳。

坝肩边坡动力响应数值模拟研究

文中采用有限元数值计算方法,模拟了某坝肩边坡在地震荷载作用下的动力响应;基于动力时程分析法,分析了该边坡在输入地震动峰值加速度0.45 g下的动应力、动应变、单元的安全度以及加速度分布规律;发现了坝肩边坡内无贯通的剪切破坏面,整体抗震性能较好,坝肩边坡具有一定的抗震稳定性安全储备,可为坝肩边坡设计提供指导。

坡折带区立体震源与平面震源资料对比分析

深水区逐步成为海洋油气资源勘探靶区,该区域地质情况复杂,中深层地震成像存在信噪比低、分辨率低的问题,势必影响油气资源的勘探开发。为提高深水区中深层地震数据的品质,从地震数据采集的源头出发,采用立体震源和平面震源在同一采集参数下,对坡折带区同一位置重复进行地震数据采集,经过相同的处理流程后,将二者在子波、炮集频谱、近道频谱、叠加剖面频谱、最终成像等方面进行对比分析。结果表明:立体震源子波在能量强度与受鬼波干扰方面都优于平面震源,且在深水区中深层具有频带更宽的特征,尤其是30~80 Hz频率更丰富,从而可以提高地震剖面的分辨率,改善地震数据的成像。由此可知,与平面震源相比,立体震源在改善深水区中深层地层成像方面具有较好的优势。因而在深水区中深层地质条件复杂的情况下,可采用立体震源采集地震数据,以提高地震数据成像品质。

雨后不同时长基覆型边坡动力失稳破坏研究

基覆型边坡由于其上部为松散型堆积体,下部为基岩的特点,在降雨和地震作用下的失稳过程和破坏特征和其他边坡有较大不同,而降雨和地震作用的间隔时间会对二者耦合作用产生较大影响。利用自制的模型箱对基覆型边坡开展振动台模型试验,研究不同降雨停止时长对边坡稳定性的影响以及边坡降雨后静止不同时长在地震作用下的失稳特征和破坏模式。试验结果表明,降雨后间隔不同时间发生地震,边坡的破坏方式均呈过渡式破坏。在达到一定降雨强度后,降雨期间边坡含水率和孔隙水压力突增,而降雨停止后随着静止时长的增加,二者不断减小,之后达到稳定状态;随着静止时长的不断增加,基覆型边坡失稳临界加速度不断增加,大致和静止时长呈一个正相关的函数关系。

川东五百梯地区石炭系岩溶古地貌识别及储集意义

综合利用钻井、测井、岩心及地震资料,通过建立地震正演模型模拟、RGB分频融合技术及波形分类分析等手段,对川东五百梯地区石炭系岩溶古地貌进行了识别与刻画。研究结果表明:(1)川东五百梯地区石炭系遭受的岩溶作用强度自西向东逐渐变小,东南部石炭系原始沉积厚度更大,但残余厚度分布不均匀,主要为10~30 m;西北部地层厚度较小,为0~15 m。(2)研究区石炭系自西向东可识别出岩溶高地和岩溶斜坡2个二级地貌单元,岩溶斜坡可划分为残丘和浅洼2个三级地貌单元,再依据其差异溶蚀特征,可进一步划分为陡斜坡浅洼和缓斜坡浅洼,浅洼内发育残丘、暗河及落水洞。反射同相轴的上提和下拉特征、岩溶角砾岩的发育、地震层拉平剖面、RGB分频融合及波形变化特征等均可识别出岩溶古地貌的发育。(3)研究区石炭系各地貌单元的分布受构造控制,浅洼和残丘多以椭圆状或不规则长条状呈北西—南东向展布,暗河的展布与浅洼长轴方向一致;岩溶古地貌控制着地层厚度以及溶蚀孔洞的发育,残丘残余厚度较大,岩溶作用强,充填作用较弱,溶蚀孔洞较发育,储层平均孔隙度为4.34%;缓斜坡浅洼残余厚度较小,充填作用较强,溶蚀孔洞不发育,储层平均孔隙度为2.68%,而陡斜坡浅洼虽然残余厚度小,但因潜水位低、泄水能力强,溶蚀作用强而充填作用弱,储集空间发育,储层平均孔隙度为5.05%;缓斜坡和陡斜坡储层平均孔隙度分别为3.67%和3.31%,岩溶高地孔隙度最小,平均为2.51%。