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1.
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. 相似文献
2.
黄土高原边坡特征与破坏规律的分区研究 总被引：5，自引：1，他引：4
为了研究黄土高原自然边坡的特征及破坏规律,按山系与水系或水系的分水岭、地貌单元、地层岩性特征等条件,将黄土高原划分为8个区:临洮—永靖区、天水—通渭区、兰州—会宁区、陇东区、靖边—安塞区、隰县—离石区、甘泉—吉县区和汾渭区.根据极限状态边坡的4个野外判别标准,测量了8个区510个自然极限状态黄土边坡断面,分区采用指数模型回归边坡坡高与坡宽的相关关系,计算各区20、50、100m坡高的边坡稳定系数和失效概率.结果表明:黄土高原的边坡特征与破坏形式具有分区特征,且南北差异性明显.临洮—永靖区边坡坡高与坡宽呈线性关系,表明该区边坡坡度不随坡高变化,边坡稳定性受内摩擦角控制;兰州—会宁区和靖边—安塞区高坡陡,低坡缓,高坡不稳定,易发生错落式滑坡;天水—通渭区、甘泉—吉县区和汾渭区高坡缓,低坡陡,稳定性计算结果显示高坡和低坡都较为稳定,但由于地层结构和地貌的特点,高边坡易发生低速蠕变型滑坡或高速远程滑坡;陇东区边坡整体上较为稳定;隰县—离石区受黏粒含量较高的Q1地层控制,高边坡稳定性较差;50m左右坡高的黄土边坡稳定性对强度指标内聚力、内摩擦角的敏感度都高,易于失稳. 相似文献
3.
Experimental study of motion characteristics of rock slopes with weak intercalation under seismic excitation 总被引：1，自引：0，他引：1
In order to investigate the effect of a weak intercalation on slope stability, a large-scale shaking table model test was conducted to study the dynamic response of rock slope models with weak intercalation. The dynamic response of the prototype slopes were studied in laboratory with the consideration of law of similitude. The initiation failure was observed in the rock slope model with a counter-tilt thin-weak intercalation firstly, not in the slope model with a horizontal thin-weak intercalation. Furthermore, it was interesting that the fracture site is shifted from crest top to the slope surface near the weak intercalation, which is different with the location of failure position in a normal layered slope. We also discussed the effect of the dip angle and the thickness of weak intercalation on the failure mechanism and instability mode of the layered rock slope. From the experimental result, it was noted that the stability of the slope with a counter-tilt weak intercalation could be worse than that of the other slopes under seismic excitation. The findings showed the difference of failure in slopes with a horizontal and counter weak intercalation, and implicated the further evaluation of failure of layered slopes caused by seismic loads. 相似文献
4.
强震中下软上硬坡体同震崩塌发育, 为了揭示这类坡体地震动的响应特征, 在珙县五同村安置了强震监测仪, 对斜坡表面和不同岩性的地震动响应进行监测, 并记录到不同方位、不同震中距的2次地震。研究表明: ①地震动响应规律有极强的方向性和距离性。2次地震相距监测站台的方向和距离不同, 使M s 4.0级地震的峰值加速度和阿里亚斯强度反而比M s 3.2级地震小。②0~30 Hz的地震波在低地山岭的高陡临空面附近有放大效应。1#监测点的主频小于3#与5#监测点, 3#监测点的主频最高。5#点的幅值范围为0.018~0.055 m/s-2, 3#点幅值范围为0.036~0.087 m/s-2, 3#点相较于5#点, 其三向最高幅值同比放大了1.58~2.0倍。③泥质砂岩的主频为4.8~8.4 Hz, 灰岩的主频为5.5~21.4 Hz, 不同的岩层共振频率不同, 灰岩对地震波的选频放大效应强于泥质砂岩。④地震波在不同高程的山岭斜坡部位具有选择放大作用, 在一定范围内高程越大地形放大效应越明显。 相似文献
5.
山西乡宁—吉县地区黄土高边坡可靠度研究 总被引：1，自引：1，他引：0
在山西乡宁—吉县地区实测了7个具有代表性的自然极限状态黄土高边坡断面,建立边坡地层结构模型;选取研究区合理的黄土物理力学参数,并分地层年代对10个典型工点的黄土强度参数内聚力和内摩擦角的变异性进行分析;选取6组典型的强度参数变异系数组合,基于Monte Carlo法进行可靠度模拟,评价该区边坡稳定性;采用自然类比法进行边坡设计.结果表明:边坡失效概率随坡高的变化趋势一致,均是中等坡高(49.8m)的边坡失效概率较大,低坡和高坡的失效概率较低;当变异系数较小时,边坡失效概率对坡高和坡度的变化敏感,而当变异系数较大时,边坡失效概率对坡高和坡度的变化不敏感;当坡型一定、强度参数变异系数较小时,边坡的稳定系数基本不变,而当参数变异系数超过某一界限时,稳定系数随变异系数的增大而增大,二者存在非线性相关关系;研究区黄土边坡处于基本稳定状态,但其失效概率最大达69.3%,平均21.1%,介于20%~30%的比例为33.3%,大于30%的比例为14.3%,可靠度指标介于-0.5~8.5,其中小于2.7的比例为88.1%;对于坡高约为50m的黄土高边坡,若取30%作为可接受失效概率,边坡坡度需降至45°以下,如果期望可接受失效概率在10%以内,则坡度不宜超过34°. 相似文献
6.
Effect of lithology and structure on seismic response of steep slope in a shaking table test 总被引：4，自引：2，他引：2
Studies on landslides by the 2008 Wenchuan earthquake showed that topography was of great importance in amplifying the seismic shaking, and among other factors, lithology and slope structure controlled the spatial occurrence of slope failures. The present study carried out experiments on four rock slopes with steep angle of 60° by means of a shaking table. The recorded Wenchuan earthquake waves were scaled to excite the model slopes. Measurements from accelerometers installed on free surface of the model slope were analyzed, with much effort on timedomain acceleration responses to horizontal components of seismic shaking. It was found that the amplification factor of peak horizontal acceleration, RPHA, was increasing with elevation of each model slope, though the upper and lower halves of the slope exhibited different increasing patterns. As excitation intensity was increased, the drastic deterioration of the inner structure of each slope caused the sudden increase of RPHA in the upper slope part. In addition, the model simulating the soft rock slope produced the larger RPHA than the model simulating the hard rock slope by a maximum factor of 2.6. The layered model slope also produced the larger RPHA than the homogeneous model slope by a maximum factor of 2.7. The upper half of a slope was influenced more seriously by the effect of lithology, while the lower half was influenced more seriously by the effect of slope structure. 相似文献
7.
风险分析与评估是解决边坡固有不确定性的重要工具, 但同时考虑外在荷载和内在岩土力学参数的不确定性, 对边坡进行系统定量风险分析的研究较少。以西藏扎拉水电站厂后倾倒变形边坡为例, 基于场地地震峰值加速度概率密度函数和不同地震峰值加速度下边坡失稳概率拟合函数, 采用数值积分计算了边坡在设计基准期的失稳概率, 并采用离散元方法对边坡失稳后的影响范围进行了数值模拟, 在此基础上进行了承灾体易损性分析及定量风险计算, 最后采用ALARP准则进行了风险评价。研究表明, 考虑地震危险性条件下, 扎拉水电站厂后倾倒变形边坡在50 a设计基准期内失稳概率为0.061 9;边坡对水电站地面厂房存在较大威胁, 相应财产风险为5 482万元; 根据ALARP准则, 边坡风险处于不可接受区, 需采取措施防范或规避风险。研究成果对于边坡治理工程决策及风险管理具有指导意义。 相似文献
8.
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9.
ZHANG Ying-bin XIANG Chen-lin CHEN Yan-long CHENG Qian-gong XIAO Li YU Peng-cheng CHANG Zhi-wang 《山地科学学报》2019,(6)
The permanent displacement of seismic slopes can be regarded as an effective criterion for stability estimation. This paper studied the characteristics of permanent displacements induced by velocity pulse-like ground motions and developed an empirical model to readily evaluate the stability of seismic slopes in a near-fault region. We identified 264 velocity pulse-like ground motions from the Next Generation Attenuation(NGA) database using the latest improved energy-based approach. All selected ground motions were rotated to the orientation of the strongest observed pulse for considering the directivity of the pulse effect, so that the most dangerous condition for slopes was considered. The results show the velocity pulse-like ground motions have a much more significant effect on permanent displacement of slopes than non-pulse-like ground motions. A regression model based on a function of peak ground velocity(PGV), peak ground acceleration(PGA) and critical acceleration(ac), was generated. A significant difference was found by comparing the presented model with classical models from literatures. This model can be used to evaluate the seismic slope stability considering the effects of nearfault pulse-like characteristics. 相似文献
10.
在边坡稳定性上极限分析中, 由于考虑了材料的理想弹塑性本构关系与相关流动法则, 相比极限平衡法更符合岩土材料的特征。在以往的二维边坡极限分析上限法中, 要求坡面形态为规则的直线, 而无论是天然边坡还是人工边坡, 边坡的坡面形态往往并非规则的直线。此外, 以往的边坡极限上限分析中得到的稳定数N s=c/γH 主要针对土坡的临界高度计算, 且未考虑孔压等外力对边坡施加的外功率。不同于传统极限平衡法采用静力学的平衡条件, 本研究针对非直线型坡面边坡稳定性问题, 假定滑动面为对数螺旋线, 基于极限分析上限定理和虚功原理, 提出了一种边坡发生旋转破坏时旋转中心的确定方法, 推导出了非直线型坡面边坡的重力虚功功率和能量平衡方程的解析解, 并提出了基于内、外功率之比的稳定系数K 用以评价边坡的稳定性。通过算例比较了不同形态天然边坡的稳定性和人工削坡对边坡稳定性的影响, 并分析了边坡的坡度(β )、土体的内摩擦角(φ )、黏聚力(c )以及孔压系数(ru )对稳定系数K 的影响规律。对于坡度较大的边坡, 通过削坡改变坡面形态提高了边坡的稳定系数K 。稳定系数K 随黏聚力的增加而非线性增大, 随孔压系数的增加而降低。当黏聚力相对于孔压系数对边坡稳定性影响更大时, 稳定系数K 随内摩擦角的增加而增大; 反之, 稳定系数K 则随内摩擦角的增加而减小。以上结果符合对边坡稳定性分析的普遍认知, 验证了模型的合理性。另外, 通过将该方法与传统的Bishop法的计算结果进行对比, 发现安全系数F s=1与稳定系数K =0的临界状态物理意义相同, 稳定系数K 随黏聚力非线性增加, 更符合边坡的渐进破坏过程。 相似文献
11.
In analyzing seismic stability of a slope with upper bound limit analysis method, the slip surface is often assumed as a log-spiral or plane slip surface. However, due to the presence of a weak layer and unfavorable geological structural surface or a bedrock interface with overlying soft strata, the preexisting slip surface of the slope may be irregular and composed of a series of planes rather than strictly log-spiral or plane shape. A computational model is developed for analyzing the seismic stability of slopes with pre-existing slip surfaces. This model is based on the upper bound limit analysis method and can consider the effect of anchor bolts. The soil or rock is deemed to follow the Mohr-Coulomb yield criterion. The slope is divided into multiple block elements along the slip surface. According to the displacement compatibility and the associated flow rule, a kinematic velocity field of the slope can be obtained computationally. The proposed model allows not only calculation of the rate of external work owing to the combined effect of self-weight and seismic loading, but also that of the energy dissipation rate caused by the slip surface, interfaces of block elements and anchorage effect of the anchors. Considering a direct relationship between the rate of external work and the energy dissipation rate, the expressions of yield acceleration and permanent displacement of anchored slopes can be derived. Finally, the validity of this proposed model is illustrated by analysis on three typical slopes. The results showed that the proposed model is more easily formulated and does not need to solve complex equations or time consuming iterations compared with previous methods based on the conditions of force equilibrium. 相似文献
12.
Slope seismic response monitoring on the aftershocks of the Wenchuan earthquake in the Mianzhu section 总被引：1，自引：0，他引：1
Previous investigations have shown that the seismic response of slopes during the Wenchuan earthquake was highly variable.The present study tries to give an answer to the question:Which are the main factors affecting the seismic response degree of slopes? With the support of the China Geological Survey Bureau,we set 3 monitoring sections in Jiulong slope,Mianzhu city,China with the aim to record the site response of the slope during the aftershocks of the Wenchuan earthquake.After the Wenchuan earthquake,which happened on 12 May 2008,30 aftershocks have been recorded in these monitoring points.We analyzed 11 records,with magnitudes ranging from ML = 4.6 to ML = 3.1.The amplification factors of the horizontal compound PGA and 3D compound PGA have been determined for the 3 points at different elevations on the slope.Results showed that the dynamic response of the slope on the earthquake was controlled by factors such as topography and the thickness of the Quaternary overburden. 相似文献
13.
As a combined supporting structure,the anchor cable and lattice beam have a complex interaction with the slope body.In order to investigate the seismic behaviors of the slope reinforced by anchor cable and lattice beam,a largescale shaking table test was carried out on a slope model(geometric scale of 1:20)by applying recorded and artificial seismic waves with different amplitudes.The acceleration and displacement of the slope,the displacement of lattice beam and the axial force of anchor cable were obtained to study the interaction between the slope and the supporting structure.The test results show that:(1)the acceleration responses of the slope at different relative elevations display obvious nonlinear characteristics with increasing of the peak ground acceleration(PGA)of the inputted seismic waves,and the weak intercalated layer has a stronger effect on acceleration amplification at the upper part of the slope than that at the lower part of the slope;(2)the frequency component near the second dominant frequency is significantly magnified by the interaction between the slope and the supporting structure;(3)the anchor cables at the upper part of the slope have larger peak and residual axial forces than that at the lower part of the slope,and the prestress loss of the anchor cable first occurs at the top of the slope and then passes down;(4)the peak and residual displacements inside the slope and on the lattice beam increase with the increase of relative elevation.When the inputted PGA is not greater than 0.5 g,the combined effect of anchor cable and lattice beam is remarkable for stabilizing the middle and lower parts of the potential sliding body.The research results can provide a reference for the seismic design of such slope and the optimization of supporting structure. 相似文献
14.
在宜宾市珙县五同村布设斜坡地震动监测仪器,采集兴文县3.1级、珙县4.5级及长宁县4.6级地震数据。对监测剖面上1#、2#监测点采集到的珙县余震地震动响应数据进行滤波和校正处理,对比分析震级、高程、方位等因素对斜坡造成的地震响应后认为：1）当地震波的半波长与山体某些特定部位之间的距离接近时,斜坡地形与地震波的波峰产生耦合作用,地形放大效应显著,达到参考点的2.765倍,此处山体更容易产生较大幅度的摇晃,造成山体地质灾害;2）分析珙县4.5级与长宁县4.6级地震得出,当地震波沿特殊部位（如山脊等）传播时,地震加速度及阿里亚斯强度更加显著;3）分析地震加速度变化得出,在地震荷载作用下,随着震级的增大,斜坡的加速度响应也会增大;4）随着高程和震级的变化,监测点的地震加速度和阿里亚斯强度随之变化,高程和震级对斜坡的地震动响应具有放大效应;5）在高程和微地貌的耦合作用下,斜坡地震加速度也具有明显的放大效应。 相似文献
15.
Cracks in rock or soil slopes influence the stability and durability of the slopes. Seismic forces can trigger slope disasters, particularly in the cracked slopes. Considering the nonlinear characteristics of materials, the more generalized nonlinear failure criterion proposed by Baker is adopted. The influence of non-dimensional strength parameters on the stability of cracked slopes under earthquakes is performed using the upper bound limit analysis. The seismic displacement is calculated by adopting the logarithmic spiral failure surface according to the sliding rigid block model. Based on the existing studies, two methods for the stability analysis of cracked slopes under earthquakes are introduced: the pseudo-static method(with the factor of safety(Fs) as an evaluation index), and the displacement-based method(with the seismic displacement as an evaluation index). The pseudo-static method can only determine the instantaneous stability state of the cracked slope, yet the displacement-based methodreflects the stability variation of cracked slopes during earthquakes. The results indicate that the nondimensional strength parameters affect the factor of safety and seismic displacement of slopes significantly. The non-dimensional strength parameter(n) controlling the curvature of strength function shapes on the slope stability is affected by other parameters. Owing to cracks, the effect of non-dimensional strength parameters on seismic displacement becomes more significant. 相似文献
16.
为研究强震作用下斜坡表面的动力放大效应, 以陕西勉县某岩质斜坡为例, 建立了三维模型。运用离散元软件3DEC, 模拟了动力条件下斜坡的变形失稳过程, 分析了斜坡表面的动力响应特征, 研究了不同地震波输入工况条件下坡体表面动力响应差异。研究结果表明: 考虑地震纵波的影响时, 竖向加速度得到显著增强, 坡面的PGA放大系数增强了约1.62倍; 坡面形态强烈影响着斜坡表面的动力响应特征, 强震作用下, 斜坡坡肩及坡形转折处的放大效应均十分强烈, 凸出部位次之, 坡表两侧的放大效应最弱; 不同输入工况下, 斜坡坡形转折处的水平向PGA放大系数均维持较高值, 特别是在仅输入水平向加速度的条件下, 该部位在地震滑坡灾害预防中应特别注意; 强震作用下滑坡的运动过程可概括为滑坡孕育启动阶段—挤压碰撞高速运动阶段—堆积阶段。研究成果可为该地区防灾减灾工作提供一定理论支持。 相似文献
17.
It is difficult to obtain reliable shear strength parameters for the stability analysis and evaluation of high loess slopes.Hence,this paper determines slope elements and physical parameter of 79 slopes with heights of[40,120]m based on the measured loess slopes in the Ganquan and Tonghuang subregions of northern Shaanxi Province,China.In the limit state of the loess slope(stability factor Fs is 1.0),a fitting equation for the slope height and width is established.Then,the model is developed by stability analysis software-SLOPE/W,and the comprehensive shear strength parameters corresponding to different slope heights of the high slope in the study area are obtained by inversion using the Morgenstern-Price method.The results show that when the height of the slope increases,the cohesion c increases in the soil,and the internal friction angle j decreases.This change is consistent with the characteristics reflected in the composition and physical properties of the slopes,and the comprehensive strength parametric curves are very similar between the Ganquan subregion and the Tonghuang subregion.A landslide that occurred in Miaodian-zaitou of Jingyang County,Shaanxi Province,is selected to verify this inversion method,and the results show that the calculated shear strength parameters of the inversion are consistent with the measured value of the actual slope. 相似文献
18.
层状反倾岩质边坡是一种常见边坡类型，其变形破坏模式多样、力学机制复杂、影响因素众多。为揭示层状反倾岩质边坡不同临空条件几何特征参数对反倾边坡倾倒变形影响规律，通过3DEC并结合数理统计系统深入研究几何特征参数对倾倒变形影响。研究表明:①反倾边坡具有3个临空面时边坡变形最大，1个临空面时边坡变形最小；②变形随边坡高度、切坡角度增大而增大，随节理面与临空面夹角的增大而减小，随岩层厚度增大先增大后减小；③2个临空面夹角90°时边坡变形最大；④1个、2个临空面时节理倾角60°时位移最大，3个临空面时随节理倾角增大而增大。 相似文献
19.
The dynamic failure mode and energy-based identification method for a counter-bedding rock slope with weak intercalated layers are discussed in this paper using large scale shaking table test and the Hilbert-Huang Transform (HHT) marginal spectrum. The results show that variations in the peak values of marginal spectra can clearly indicate the process of dynamic damage development inside the model slope. The identification results of marginal spectra closely coincide with the monitoring results of slope face displacement in the test. When subjected to the earthquake excitation with 0.1 g and 0.2 g amplitudes, no seismic damage is observed in the model slope, while the peak values of marginal spectra increase linearly with increasing slope height. In the case of 0.3 g seismic excitation, dynamic damage occurs near the slope crest and some rock blocks fall off the slope crest. When the seismic excitation reaches 0.4 g, the dynamic damage inside the model slope extends to the part with relative height of 0.295-0.6, and minor horizontal cracks occur in the middle part of the model slope. When the seismic excitation reaches 0.6 g, the damage further extends to the slope toe, and the damage inside the model slope extends to the part with relative height below 0.295, and the upper part (near the relative height of 0.8) slides outwards. Longitudinal fissures appear in the slope face, which connect with horizontal cracks, the weak intercalated layers at middle slope height are extruded out and the slope crest breaks up. The marginal spectrum identification results demonstrate that the dynamic damage near the slope face is minor as compared with that inside the model slope. The dynamic failure mode of counter-bedding rock slope with weak intercalated layers is extrusion and sliding at the middle rock strata. The research results of this paper are meaningful for the further understanding of the dynamic failure mode of counter-bedding rock slope with weak intercalated layers. 相似文献
20.
Large-scale shaking table tests were conducted to study the dynamic response of a slope reinforced by double-row anti-sliding piles and prestressed anchor cables. The test results show that the reinforcement suppressed the acceleration amplification effectively. The axial force time histories are decomposed into a baseline part and a vibration part in this study. The baseline part of axial force well revealed the seismic slope stability, the peak vibration values of axial force of the anchor cables changed significantly in different area of the slope under seismic excitations. The peak lateral earth pressure acting on the back of the anti-sliding pile located at the slope toe was much larger than that acting on the back of the anti-sliding pile located at the slope waist. The test results indicate an obvious load sharing ratio difference between these two anti-slide piles, the load sharing ratio between the two anti-sliding piles located at the slope toe and the slope waist varied mainly in a range of 2-5. The anti-slide pile at the slope waist suppressed the horizontal displacement of the slope surface. 相似文献