基于颗粒流的地震液化型滑坡运动学特征分析

掌握滑坡运动学特征,针对运动学特征提出防治措施是减轻滑坡灾害的关键。在野外调查资料与土工试验的基础上,基于颗粒流离散元方法,研究了西吉县兴平乡堡湾村下马达子滑坡的发生过程,探索了黄土地震液化型滑坡的发生机理和运动规律,通过与未液化的地震滑坡进行对比,分析了地震液化对滑坡运动的影响,归纳地震液化型滑坡的运动学特征。具体分析结论如下：（1）液化模型较未液化模型更容易发生失稳破坏,速度更大、滑距更远、破坏性更强;（2）无论是液化模型还是未液化模型,坡肩位置都是地震滑坡发生失稳的关键部位;（3）斜坡液化后,在液化区附近的区域滑体会推动和冲击下部滑坡体,造成斜坡更大面积的失稳,这是液化型地震滑坡具有低角度,强破坏力特征的原因之一。     

海原大地震诱发石碑塬黄土滑坡机制探讨

1920年海原8.5级大地震诱发的石碑黄土塬滑坡,因其规模大、坡度小、滑距远的特点成为业界关注焦点,目前对该滑坡的物理力学过程仍无统一认识。基于此,文章通过理论分析和数值计算方法研究该滑坡初始状态、地震动力响应和流滑发展过程。为分析震前斜坡初始状态,建立考虑斜坡表面拉裂缝中侧向水压力作用的力学计算模型。结果表明,拉裂缝中侧向水压力削弱了斜坡整体稳定状态;为研究地震时斜坡动力响应过程,建立数值计算模型,获得地震时斜坡饱和土层的孔隙水压力比和斜坡位移的变化特性;为解释远程滑坡,将液化后土层等效为流体,借鉴泥流滑距估算理论,求算石碑塬滑坡的滑距,计算结果与前人现场考察结果吻合。     

汶川地震地表破裂带北端部抛射型滑坡特征及其机制

5.12汶川8级地震在直接带来巨大灾害的同时,还激发了大量的次生地质灾害,比如滑坡、泥石流和滚石等,这更加剧了地震灾害的程度。东河口滑坡便是这些次生地质灾害中比较独特的一例,该滑坡发生在四川省青川东河口地区,这里也正好是汶川地震地表破裂带的北部端点。作为一例发生在特殊部位的由地震引发的抛射型滑坡,它具有和由纯重力或者暴雨引起的滑坡明显不同的特点:其一,没有统一连续的滑动面,而是由上部比较深的和下部比较浅的明显分开的两段滑动面组成;其二,由于巨大的地震水平和垂直加速度,滑坡起始于上部滑坡体的抛射,因此称为抛射型滑坡。野外调查及分析结果表明:以地表破裂带为界,滑坡区和羽状裂缝分布区非常规则地分布其两侧,这种分布为地表破裂的形成过程所控制,也即是受到断层错动的控制,因此,在特定的地貌及地质条件的控制下,滑坡的发生为走滑断层构造地貌形成过程以及局部构造应力变化过程的必然结果。本文在综合分析了滑坡发生的地质地貌条件的同时,利用简单的走滑断层构造地貌产生模型解释了东河口大型抛射型滑坡的发生机制及其运动过程。研究结果表明:在评估地震激发的大型滑坡灾害的过程中,除了需要考虑地震动、水平加速度以及地质地貌条件之外,考虑垂直加速度以及滑坡所发生的特殊的地貌部位也显得十分必要。     

基于颗粒流方法的黄土地震滑坡数值模拟

基于颗粒流理论研究土质边坡动力稳定性及其滑动过程是近年来滑坡研究的一个新热点。在野外调查和室内试验的基础上,通过标定土体细观参数、模型建立、动力输入、动态监测等过程,利用PFC2D程序模拟了西吉县兴平乡堡湾村下马达子滑坡的失稳破坏运动过程,得到了该滑坡的破坏运动机理。得到如下结论：(1)下马达子滑坡的失稳机制是在地震作用下斜坡前缘牵引、后缘推挤,使得坡肩受拉发生破坏,失稳后坡肩位置较大的速度和位移是地震滑坡破坏力强、致灾范围大的主要原因;(2)黄土地震滑坡的滑坡后壁相对平缓,这是区别于重力滑坡的重要特征之一;(3)颗粒流模拟得到的滑坡前后相对高差和长度与实际情况较为吻合,因此,颗粒流方法可以用于地震滑坡滑距的预测。     

汶川地震高速远程滑坡速度研究

汶川地震诱发了大量的高速远程滑坡。在超强的地震动作用下,坡体结构被撕裂并抛射后,受到坡体前缘地形及自身势能的影响,很容易转化为碎屑流作远程运动,这种高位滑坡以其很快的运动速度和超常的运动距离造成了巨大的灾害与损失。本文在对汶川地震大型典型高速远程滑坡大量现场调查的基础上,分析了坡体临空飞行运动初始速度、滑程运动最大速度以及碎屑流运动速度,并且以东河口滑坡为例,对比了不同计算方法下的运动速度和运动性,得到东河口滑坡的运动特征值μ=0.2292,最大运动速度Vm ax=63.40 m/s,平均运动速度超过25 m/s,属于超高速滑坡运动以及强碎屑流性质。     

喜家湾地震黄土滑坡形成机理

在喜家湾滑坡现场调查基础上,采集黄土斜坡的原状黄土和滑坡滑带土试样进行了室内试验,分析计算了滑坡土体震陷性和液化可能性;并结合滑坡发生前斜坡在地震作用下的稳定性分析及数值模拟,对该滑坡的形成机理进行了研究。研究表明,地震发生时,斜坡上部黄土产生震陷,结构破坏,下部泥岩面附近处于饱和状态的黄土在很短时间内产生了液化现象,坡体下滑形成震陷—液化复合型滑坡。     

黄土斜坡震害面波勘探调查及其动力稳定性分析——以甘肃岷县、漳县M_s6.6地震为例

2013年7月22日,甘肃省定西市岷县、漳县交界处发生6.6级地震,地震诱发了约600余处地质灾害(隐患点),其中规模最大的是岷县梅川镇永光村四社西的两个相邻滑坡。本文对永光村西侧滑坡进行了多种手段的现场勘测,特别是在坡顶及坡底开展了高密度面波勘探,分析了该黄土滑坡成因及滑坡附近的地形、地层等因素。采用动力有限元法和强度折减法结合的方法分析该滑坡在地震荷载作用下的动力响应、滑坡动力稳定性的影响因素以及地震荷载与滑坡失稳状态之间的关系。结果表明,由于地震前的强降雨导致表层黄土的抗剪强度降低,在地震荷载作用下黄土层之间存在拉应力效应并导致崩塌滑动。     

沙土在孔隙水注入实验中渗透剪切破坏

前人曾指出液化后伴随着超孔隙水压重新分配的渗透会引起流体破坏的可能性。为了研究这一现象,利用实验室三轴试验将孔隙水注入土壤检测了土壤的渗透剪切破坏。该实验是在各项异性的固结作用后保持差应力,使用孔隙水控制装置在体积不变的应变控制条件下将孔隙水注入。实验中所用的材料是在1995年神户地震时被液化的常规洁净细砂和风化的花岗岩土壤。本文以实验结果为基础,讨论了由孔隙水注入引起的渗透剪切破坏判据和导致后液化行为的剪切应变发展特征。     

岩石摩擦-滑动中的声发射b值动态特征及其地震学意义

双剪试验的结果表明,岩石摩擦滑动过程中的AE b 值动态曲线可归纳为锯齿状和台柱状两类,分别对应于不规则粘滑和规则粘滑.滑动瞬间滑面上摩擦系数变化△μ的分布决定岩石的滑动方式,不均匀分布易发生不规则粘滑.均匀分布易引起规则粘滑;破裂和滑动是摩擦滑动过程中的两类AE 机制,两类AE 的能量分别与破裂面面积及△μ成正比.研究结果提示,平直光滑的地震断层可能显示出特征地震的发震特点.     

金沙江矮子沟巨型古滑坡形成机制及运动过程研究

通过详细的野外调查，并结合遥感解译、室内试验以及数值模拟等手段，对矮子沟巨型古滑坡的基本特征、形成机制及运动演化过程进行了深入研究。矮子沟古滑坡的形成条件为：滑坡剪出口与坡脚之间存在巨大的高差，为滑坡的形成创造了良好的临空条件；顺向岸坡结构以及坡体内发育的多组控制性结构面是滑坡发生的结构基础；玄武岩系中的凝灰岩软弱夹层削弱了岩体的完整性，地表水及地下水长期入渗，水的软化作用降低了软弱夹层的抗剪强度；地震作用是造成岩体最终滑动失稳的关键因素。该滑坡的动力学过程可划分为四个阶段：(1)启程活动阶段。斜坡地形效应使得地震波在斜坡上部表现出异常放大现象，当短时间内积聚的振动能量超过岩土体的强度时，易形成高位滑坡，滑坡的变形破坏机制为拉裂-滑移；(2)近程活动阶段。近3.82×10⁸ m³的滑坡物质高位高速下滑，与矮子沟右岸坡体发生猛烈碰撞后进一步碎裂解体；(3)高速远程碎屑流阶段。碎屑流继续沿矮子沟高速运动约3 km；(4)堆积堵江阶段。滑坡物质最终形成体积为2.73×10⁸ m³的巨型堰塞坝，堵塞金沙江并...     

Landslide Amplification by Liquefaction of Runout‐Path Material after the 2008 Wenchuan (M 8·0) Earthquake,China

Here, we propose that an earthquake can trigger the failure of a landslide mass while simultaneously triggering liquefaction of runout‐path materials before the arrival of the landslide mass, thus greatly increasing the size and mobility of an overriding landslide. During the 2008 Wenchuan earthquake, about 60 000 landslides were triggered, directly resulting in about 20 000 casualties. While these landslides mainly originated from steep slopes, some landslides with high mobility formed in colluvial valley deposits. Among these, the most catastrophic was the Xiejiadian landslide in Pengzhou city, which traveled hundreds of meters before coming to rest. Through field investigation and laboratory testing, we conclude that this landslide primarily formed from colluvial deposits in the valley and secondarily from failure of slopes in granitic rock located uphill. Much of the granitic slope failure was deposited in the upper part of the travel path (near the slide head); the remainder was dispersed throughout the main landslide deposit. Superposition of deposits at the landslide toe indicates that landslide debris derived from colluvial soil was deposited first. The deposits at the landslide toe displayed flow characteristics, such as fine materials comprising basal layers and large boulders covering the deposit surface. We hypothesize that the main part of the landslide resulted from seismogenic liquefaction of valley colluvium, rather than from liquefaction potentially caused by undrained loading from the granitic slope failures impacting the colluvium. To examine the likelihood that seismogenic liquefaction occurred, we took samples from different areas of the landslide deposit and performed undrained cyclic shear tests on them in the laboratory. The results showed that the sandy soils that comprise most of the deposit are highly liquefiable under seismic loading. Therefore, we conclude that liquefaction of the colluvium in the valley during the earthquake was the main reason for this rapid (~46 m/s) long‐runout (1·7 km) landslide. Copyright © 2012 John Wiley & Sons, Ltd.     

Shear wave velocity-based liquefaction evaluation in the great Wenchuan earthquake： a preliminary case study

The great Wenchuan earthquake (Ms = 8.0) in 2008 caused severe damage in the western part of the Chengdu Plain. Soil liquefaction was one of the major causes of damage in the plain areas, and proper evaluation of liquefaction potential is important in the definition of the seismic hazard facing a given region and post-earthquake reconstruction. In this paper, a simplified procedure is proposed for liquefaction assessment of sandy deposits using shear wave velocity (Vs), and soil liquefaction from the Banqiao School site was preliminarily investigated after the earthquake. Boreholes were made at the site and shear wave velocities were measured both by SASW and down-hole methods. Based on the in-situ soil information and Vs profiles, the liquefaction potential of this site was evaluated. The results are reasonably consistent with the actual field behavior observed after the earthquake, indicating that the proposed procedure is effective. The possible effects of gravel and fines contents on liquefaction of sandy soils were also briefly discussed.     

Seismic loading impacts on excess pore‐water pressure maintain landslide triggered flowslides

During the 2003 Sanriku‐Minami earthquake, Japan, a flowslide was triggered on a slope of about 13.5º. The displaced landslide mass developed into a flowslide and deposited on a horizontal rice paddy after traveling approximately 130 m. To study the trigger and movement mechanisms of this landslide, field investigation and laboratory ring‐shear tests were performed. Field investigation revealed that the landslide originated from a fill slope, where a gully was buried for cultivation some decades ago, and shallow ground water was present. Undrained monotonic and cyclic ring‐shear tests on a sample (pyroclastic deposits) taken from the source area revealed that the soil is highly liquefiable, and its steady‐state shear strength can be little affected by overconsolidation. Using the seismic records of the earthquake, probable seismic loadings on the sliding surface were synthesized and applied to the samples in ring‐shear tests, which were performed under undrained or partially drained conditions. The undrained and partially drained tests revealed that shear failure can be triggered by the introduction of seismic loading and formation of excess pore‐water pressure. The generation of excess pore‐water pressure along with increase of shear displacement and the inhibited dissipation of excess pore‐water pressure due to the thickness of the saturated soil layer above the sliding surface probably enabled the continued post‐failure landsliding. Copyright © 2008 John Wiley & Sons, Ltd.     

非饱和黄土动力液化研究——以党家岔滑坡为例

黄土具有极强的水敏性和动力易损性，黄土地区多次强震都引起过液化、滑坡等地质灾害，造成了严重的人员伤亡和财产损失，因此振动作用下高含水率黄土的液化问题不容忽视。在大量已有研究的基础上，以宁夏党家岔滑坡为例，研究振动作用下高含水率黄土的液化问题。现场调查发现高含水率滑带土并未达到完全饱和状态（饱和度达95%左右），在新鲜的芯样断面发现有明显的"流态化"液化破坏特征。借助室内试验和数值模拟技术，对党家岔滑坡非饱和黄土层的液化性能及液化发生机理进行分析。结果表明：（1）非饱和黄土层液化发生机理可概括为：地震作用下饱和黄土层孔隙水压力激增，高含水率非饱和黄土层孔压增长响应滞后，随着孔隙水压朝上部消散，地下水向上渗流，当平均有效应力接近0时，高含水率非饱和黄土层发生液化；（2）振动过程中不同饱和度黄土孔隙水压力增长响应具有滞后性，借鉴饱和黄土液化时孔压比的判别标准和Seed简化判别法，初步证实党家岔滑坡高含水率非饱和黄土层可发生振动液化，斜坡前缘和中部土体发生液化的初始饱和度范围分别为68.3%~100%和73.8%~100%，斜坡后缘土体不发生液化。     

国内外液化砂砾土土性对比分析

砂土液化问题的研究特别是砂土液化的判别目前已经取得了较大的进展,并在国内外现行的规范中充分反映,而砂砾土由于颗粒大、透水性好,普遍认为地震时孔压不至于上升至液化的程度,往往将其划分为非液化土类。通过调查汶川地震砂砾土液化情况以及勘察试验获取其土性资料,对比分析了国内外液化砂砾土的地质背景及土性特征。主要认识为：①以往国内外砂砾土液化实例虽然有限,但已经表明松散-稍密的砂砾土在一定的地震强度下仍有可能发生液化,而2008年汶川地震中的大量砂砾土液化的事实,说明笼统地将砂砾土划归为非液化土类的做法有误;②汶川地震液化砂砾土的颗粒级配范围涵盖了国内外其他地震的颗粒级配,研究汶川地震的砂砾土液化问题具有代表性和普遍性,以此建立的砂砾土液化评价方法在国际上应具有通用性。     

Cyclic resistance and liquefaction behavior of silt and sandy silt soils

The liquefaction behavior and cyclic resistance ratio (CRR) of reconstituted samples of non-plastic silt and sandy silts with 50% and 75% silt content are examined using constant-volume cyclic and monotonic ring shear tests along with bender element shear wave velocity (V_s) measurements. Liquefaction occurred at excess pore water pressure ratios (r_u) between 0.6 and 0.7 associated with cumulative cyclic shear strains (γ) of 4% to 7%, after which cyclic liquefaction ensued with very large shear strains and excess pore water pressure ratio (r_u>0.8). The cyclic ring shear tests demonstrate that cyclic resistance ratio of silt and sandy silts decreases with increasing void ratio, or with decreasing silt content at a certain void ratio. The results also show good agreement with those from cyclic direct simple shear tests on silts and sandy silts. A unique correlation is developed for estimating CRR of silts and sandy silts (with more than 50% silt content) from stress-normalized shear wave velocity measurements (V_s1) with negligible effect of silt content. The results indicate that the existing CRR–V_s1 correlations would underestimate the liquefaction resistance of silts and sandy silt soils.     

Characterization of liquefaction resistance in gravelly soil: large hammer penetration test and shear wave velocity approach

Gravelly soil is generally recognized to have no liquefaction potential. However, liquefaction cases were reported in central Taiwan in the 1999 Chi-Chi Taiwan earthquake and in the 1988 Armenia earthquake. Thus, further studies on the liquefaction potential of gravelly soil are warranted. Because large particles can impede the penetration of both standard penetration test and cone penetration test, shear wave velocity-based correlations and large hammer penetration tests (LPT) are employed to evaluate the liquefaction resistance of gravelly soils. A liquefied gravelly deposit site during the Chi-Chi earthquake was selected for this research. In situ physical properties of soil deposits were collected from exploratory trenches. Instrumented LPT and shear wave velocity (V_s) measurements were performed to evaluate the liquefaction resistance. In addition, large-scale cyclic triaxial tests on remolded gravelly soil samples (15 cm in diameter, 30 cm in height) were conducted to verify and improve LPT-based and V_s-based correlations. The results show that the LPT and shear wave velocity methods are reasonably suitable for liquefaction assessment of gravelly soils.     

A prediction model for horizontal run-out distance of landslides triggered by Wenchuan earthquake

The peak ground acceleration (PGA), the volume of a sliding mass V, the height of a mountain H _L and the slope angle θ of a mountain are four important parameters affecting the horizontal run-out distance of a landslide L. Correlations among them are studied statistically based on field investigations from 67 landslides triggered by the ground shaking and other factors during the Wenchuan earthquake, and then a prediction model for horizontal run-out distance L is developed in this study. This model gives due consideration to the implications of the above four parameters on the horizontal run-out distance L and the validity of the model is verified by the Donghekou and Magong Woqian landslides. At the same time, the advantages of the model are shown by comparing it with two other common prediction methods. The major findings drawn from the analyses and comparisons are: (1) an exponential relationship exists between L and log V, L and log H _L, L and log PGA separately, but a negative exponential relationship exists between L and log tanθ, which agrees with the statistical results; and (2) according to the analysis results of the relative relationship between the height of a mountain (H) and the place where the landslides occur, the probabilities at distances of 2H/3-H, H/3-2H/3, and 0-H/3 are 70.8%, 15.4%, and 13.8%, respectively, revealing that most landslides occurred at a distance of H/2-H. This prediction model can provide an effective technical support for the prevention and mitigation of landslide hazards.     

汶川8.0级地震环境剪应力特征研究

基于甘肃强震固定台和流动观测记录的汶川8.0级地震主震及余震加速度资料,选用三分向记录均完整的87次地震(震级范围为3.0~8.0级),根据用位错理论二维断裂模式推导的震源峰值加速度与环境剪应力关系式计算汶川地震序列的环境剪应力值,探讨其环境剪应力场特征。结果表明,环境剪应力和矩震级有较好的相关性,3~5级地震对应的应力值多在3~6 MPa,5~6级多在6~9 MPa,6~7级多在9MPa以上,且环境剪应力对震源深度也有较强的依赖性。