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1.
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.  相似文献   

2.
汶川地震高速远程滑坡机制实验研究   总被引：5，自引：0，他引：5       下载免费PDF全文
汶川大地震触发了多处高速远程滑坡,导致了大量的人员伤亡及财产损失。其中,东河口滑坡是这次地震触发的最为典型的高速远程滑坡之一,同时也是目前备受关注、争论颇多的滑坡之一。野外调研结果表明,该滑坡的成因和动力特征主要包括震裂溃屈、水平抛射、碎屑流化和振动液化等4个方面。为了对该滑坡滑动过程中的振动液化这一动力特征进行模拟再现,在东河口滑坡体上采集了具有代表性的滑带土作为试验样品,并以该地震时的实测地震波作为动力输入,利用目前国际上最先进的DPRI环剪试验机,对滑坡滑动过程中的振动液化现象进行了一系列环剪试验研究。结果表明,地震作用过程中,发生在滑坡潜在滑面上的振动液化现象是导致高速远程滑坡产生的一个重要因素;伴随着振动液化过程,滑体的剪切强度迅速降低并产生逐渐增大的剪切位移,为高速远程滑坡的形成提供了条件  相似文献   

3.
Flowslides that override a liquefied substrate can vastly enhance a disaster after failure initiation. These effects may result from the rapid velocity and long runout distance from slides mobilized into flows. It is thus crucial to provide an improved understanding of the transformation mechanisms of catastrophic flowslides for hazard evaluation. This study examines the Saleshan landslide in Gansu, China, which occurred in 1983 and killed more than 200 people. The Saleshan landslide travelled for approximately 1 km due to pore water pressure generation resulting from overrunning and liquefication of the alluvial sands in the river valley below. We used geomorphologic and topographic maps to determine its dynamic features and mobilization behaviors on the landslide body, and placemarks and seismic signals to identify its approximate velocity at different sites. Electrical resistivity tomography (ERT) surveys also revealed the hydrogeological conditions post-landslide, showing a clear groundwater table along with the liquefied alluvial sand and gravel layers. Particle size distributions and triaxial shear behaviors confirmed more ready liquefaction of superficial loess and underlying alluvial sand in comparison with the red soil above and below them. Novel loading impact triaxial testing was also performed on the alluvial sand to elucidate its liquefaction potential in undrained and drained conditions. The alluvial sand was found to be markedly prone to liquefaction in undrained conditions due to impact-induced increased pore water pressure. The results further demonstrated that the Saleshan landslide underwent a transformation from a slowing slide on a steep slope, where it originated, to flow on a nearly flat terrace with abundant groundwater that it overrode. The transformation mechanism involved the liquefied alluvium sand substrate, which greatly enhanced the landslide mobility. Along with recent, similar findings from landslides globally, substrate liquefaction may result in a widespread, significant increase in landslide mobility and thus hazard, and the present study identifies the requisite conditions for this phenomenon to occur.  相似文献   

4.
— Submarine and shoreline slope failures that accompany large earthquakes and large tsunamis are triggered by several mechanisms. Triggering mechanisms range from direct effects, such as inertial forces from earthquake shaking, to indirect effects, such as rapid drawdown that occurs when an earthquake-generated tsunami first approaches a shoreline. Soil shear strength also plays an important role in earthquake-related slope failures. Earthquakes change the shear strength of the soil by inducing excess pore water pressures. These excess pore water pressures change with time after the earthquake, resulting in changes in shear strength and slope stability with time. This paper reviews earthquake-related triggering mechanisms for submarine and shoreline slope failures. The variation in shear strength with time following an earthquake is examined and it is shown that delayed slope failures after an earthquake can occur as a result of changes in earthquake-induced excess pore water pressures and shear strength with time.  相似文献   

5.
This paper uses the catastrophic landslide that occurred in Zhongxing Town, Dujiangyan City, as an example to study the formation mechanism of landslides induced by heavy rainfall in the post-Wenchuan earthquake area. The deformation characteristics of a slope under seismic loading were investigated via a shaking table test. The results show that a large number of cracks formed in the slope due to the tensile and shear forces of the vibrations, and most of the cracks had angles of approximately 45° with respect to the horizontal. A series of flume tests were performed to show how the duration and intensity of rainfall influence the responses of the shaken and non-shaken slopes. Wetting fronts were recorded under different rainfall intensities, and the depth of rainfall infiltration was greater in the shaken slope than in the non-shaken slope because the former experienced a greater extreme rainfall intensity under the same early rainfall and rainfall duration conditions. At the beginning of the rainfall infiltration experiment, the pore water pressure in the slope was negative, and settling occurred at the top of the slope. With increasing rainfall, the pore water pressure changed from negative to positive, and cracks were observed on the back surface of the slope and the shear outlet of the landslide on the front of the slope. The shaken slope was more susceptible to crack formation than the non-shaken slope under the same rainfall conditions. A comparison of the responses of the shaken and non-shaken slopes under heavy rainfall revealed that cracks formed by earthquakes provided channels for infiltration. Soil particles in the cracks of slopes were washed away, and the pore water pressure increased rapidly, especially the transient pore water pressure in the slope caused by short-term concentrated rainfall which decreased rock strength and slope stability.  相似文献   

6.
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。  相似文献   

7.
Knowledge of the mechanisms of rain‐induced shallow landslides can improve the prediction of their occurrence and mitigate subsequent sediment disasters. Here, we examine an artificial slope's subsurface hydrology and propose a new slope stability analysis that includes seepage force and the down‐slope transfer of excess shear forces. We measured pore water pressure and volumetric water content immediately prior to a shallow landslide on an artificial sandy slope of 32°: The direction of the subsurface flow shifted from downward to parallel to the slope in the deepest part of the landslide mass, and this shift coincided with the start of soil displacement. A slope stability analysis that was restricted to individual segments of the landslide mass could not explain the initiation of the landslide; however, inclusion of the transfer of excess shear forces from up‐slope to down‐slope segments improved drastically the predictability. The improved stability analysis revealed that an unstable zone expanded down‐slope with an increase in soil water content, showing that the down‐slope soil initially supported the unstable up‐slope soil; destabilization of this down‐slope soil was the eventual trigger of total slope collapse. Initially, the effect of apparent soil cohesion was the most important factor promoting slope stability, but seepage force became the most important factor promoting slope instability closer to the landslide occurrence. These findings indicate that seepage forces, controlled by changes in direction and magnitude of saturated and unsaturated subsurface flows, may be the main cause of shallow landslides in sandy slopes. Copyright © 2013 John Wiley & Sons, Ltd.  相似文献   

8.
The 1927 Gulang M8.0 earthquake has triggered a huge number of landslides, resulting in massive loss of people''s life and property. However, integrated investigations and results regarding the landslides triggered by this earthquake are rare; such situation hinders the deep understanding of these landslides such as scale, extent, and distribution. With the support of Google Earth software, this study intends to finish the seismic landslides interpretation work in the areas of Gulang earthquake (VIII-XI degree) using the artificial visual interpretation method, and further analyze the spatial distribution and impact factors of these landslides. The results show that the earthquake has triggered at least 936 landslides in the VIII-XI degree zone, with a total landslide area of 58.6 km2. The dense area of seismic landslides is located in the middle and southern parts of the X intensity circle. Statistical analysis shows that seismic landslides is mainly controlled by factors such as elevation, slope gradient, slope direction, strata, seismic intensity, faults and rivers. The elevation of 2 000-2 800 m is the high-incidence interval of the landslide. The landslide density is larger with a higher slope gradient. East and west directions are the dominant sliding directions. The areas with Cretaceous and Quaternary strata are the main areas of the Gulang seismic landslides. The X intensity zone triggered the most landslides. In addition, landslides often occur in regions near rivers and faults. This paper provides a scientific reference for exploring the development regularities of landslides triggered by the 1927 Gulang earthquake and effectively mitigating the landslide disasters of the earthquake.  相似文献   

9.
The November 3, 2002 Denali-Alaska earthquake (Mw=7.9) caused significant liquefaction associated damage to various infrastructure built on fine-grained soils. The seismic response, liquefaction potential, and excess pore pressure generation of soils in cold regions, especially those of fine-grained nature, have not been studied thoroughly and therefore are not well-understood. This paper presents results from an extensive laboratory study on the characteristics of excess pore pressure generation and liquefaction potential of fine-grained soils. Laboratory-constituted soils specimens were tested in four categories: (1) tests on specimens subjected to no thermal conditioning or freeze–thaw cycles; (2) tests on specimens conditioned at 24, 5, 1, 0.5, and −0.2 °C; (3) tests on specimens subjected to 1–4 freeze–thaw cycles; and (4) tests on specimens conditioned at near-freezing temperatures of 0.5 and −0.2 °C through different freeze–thaw paths. Strain-controlled, undrained, cyclic triaxial tests were performed at shear strain levels of 0.005–0.8%. Specimens conditioned at different temperatures were found to generate significantly different pore pressures with cyclic loading. The excess pore pressure generation at near or slightly below freezing was found to change dramatically. A transitional change in the dynamic soil behavior, attributed to unfrozen- or frozen-dominant pore water, was discovered. The threshold shear strain was also found to be influenced by the temperature. Subjecting the soil specimens to 1, 2 and 4 freeze–thaw cycles caused a reduction in excess pore pressure generation and slight change in the threshold shear strain. The temperature conditioning path to reach the target temperature was found to be important on the development of excess pore pressure at near and slightly below-freezing temperatures.  相似文献   

10.
The Mechanical Coupling of Fluid-Filled Granular Material Under Shear   总被引：1，自引：0，他引：1  
The coupled mechanics of fluid-filled granular media controls the physics of many Earth systems, for example saturated soils, fault gouge, and landslide shear zones. It is well established that when the pore fluid pressure rises, the shear resistance of fluid-filled granular systems decreases, and, as a result, catastrophic events such as soil liquefaction, earthquakes, and accelerating landslides may be triggered. Alternatively, when the pore pressure drops, the shear resistance of these geosystems increases. Despite the great importance of the coupled mechanics of grain–fluid systems, the basic physics that controls this coupling is far from understood. Fundamental questions that must be addressed include: what are the processes that control pore fluid pressurization and depressurization in response to deformation of the granular skeleton? and how do variations of pore pressure affect the mechanical strength of the grains skeleton? To answer these questions, a formulation for the pore fluid pressure and flow has been developed from mass and momentum conservation, and is coupled with a granular dynamics algorithm that solves the grain dynamics, to form a fully coupled model. The pore fluid formulation reveals that the evolution of pore pressure obeys viscoelastic rheology in response to pore space variations. Under undrained conditions elastic-like behavior dominates and leads to a linear relationship between pore pressure and overall volumetric strain. Viscous-like behavior dominates under well-drained conditions and leads to a linear relationship between pore pressure and volumetric strain rate. Numerical simulations reveal the possibility of liquefaction under drained and initially over-compacted conditions, which were often believed to be resistant to liquefaction. Under such conditions liquefaction occurs during short compactive phases that punctuate the overall dilative trend. In addition, the previously recognized generation of elevated pore pressure under undrained compactive conditions is observed. Simulations also show that during liquefaction events stress chains are detached, the external load becomes completely supported by the pressurized pore fluid, and shear resistance vanishes.  相似文献   

11.
基于室内试验获取黄土滑坡的静力和动力力学强度参数,建立低角度黄土滑坡破坏大型物理模拟试验模型,结合FLAC3D有限差分软件,分析黄土滑坡的动力响应规律和宏观破坏特性,阐明在地震作用下黄土滑坡的失稳演化规律,揭示黄土滑坡滑体运动迁移路径。结果表明：低角度黄土-泥岩滑坡在地震荷载作用下地震波水平方向和垂直方向均出现明显的放大效应;在黄土层内部,随着斜坡高度增加,坡肩和斜坡后缘加速度放大效应较为明显,对比坡脚、坡腰和坡肩处剖面上加速度放大系数,下伏泥岩对地震波产生一定的放大效应。松弛拉张裂隙,土体强度降低,接触面和坡肩、斜坡后缘处的拉张裂缝形成弧形滑移面,上覆黄土层由内向外依次连带下滑,坡肩处土体的下滑力和地震力促使坡腰土体大面积长距离滑动,最大滑动涉及范围长达200 m左右,土体下滑至坡脚发生堆积并产生隆起。数值模拟结果和振动台试验结果在动力响应和宏观变形破坏特征均呈现较高的吻合度。  相似文献   

12.
Most of the documented slope failures triggered by the 1980 Irpinia earthquake (Ms 6.9) occurred in the upper Sele valley epicentral area (southern Italy). The early investigations revealed some puzzling characteristics of the slope failure distribution, i.e., (i) the higher landslide concentration on the valley slopes located farther away from the earthquake fault; (ii) the predominance of re-activations over first-time movements. The analyses of factors controlling the landslide concentrations indicates that the differences in hydrological setting and in slope were the two main causal factors whereas the seismic shaking, according to the radiation pattern modelling, could have been characterised by a relatively low rate of decrease across the valley. The aspect of the slopes did not play a significant role. The differences in groundwater conditions between the western and eastern valley sides were probably enhanced by the earthquake. In addition to the probable pore-water pressure rise, the seismic shaking caused large increases in the flow of springs draining the western aquifer, and this made the adjacent flysch slopes more prone to landsliding. Data from the available literature suggest that the effects of earthquake-induced groundwater release on seismic landslide distribution is especially important for normal-fault events. The Sele valley case also indicates that the slope of the pre-existing landslides is an important factor controlling their susceptibility to seismic re-activations.  相似文献   

13.
The study covered by this paper was focused on the historical case of the Calitri landslide, which was repeatedly reactivated by earthquakes, as reported since 1694. The town of Calitri (Southern Italy) is located on a ridge whose southern slope, from its top to the Ofanto river valley floor, has been historically affected by major landsliding. The last record of recurrence of the Calitri landslide leads back to the 1980 Irpinia earthquake, which caused significant damage to the town and had pervasive and visible ground effects. Based on a detailed historical reconstruction of landsliding and seismicity at Calitri, the study analysed the current static and dynamic stability of the landsliding slope by means of a finite-difference numerical analysis, taking into account the various factors of landslide initiation and kinematics. The results of the numerical analysis: (i) were consistent with the roto-translational mechanism observed upon the latest reactivation of the landslide; (ii) demonstrated that excess pore pressure redistribution caused a lag between the seismic trigger and the initiation of landsliding; and (iii) showed the impact of seismic input frequency on propagation and depth of slope instability.  相似文献   

14.
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。  相似文献   

15.
Flow and deformation failure of sandy slopes   总被引：2，自引：0，他引：2  
The effects of earthquake induced pore pressure on seismic and post seismic stability conditions of cohesionless slopes are investigated with reference to the infinite slope scheme. In cohesionless slopes the shear strength reduction caused by pore pressure build-up may lead the slope to a deformation failure or to a flow failure if liquefaction conditions are approached. Two critical values of the seismic induced pore pressure ratio are introduced to evaluate the effect of shear strength reduction on the slope failure mechanism. The results are given in the form of stability charts and a procedure for the evaluation of the seismic stability condition is described. The procedure gives useful information about the failure mechanism that slopes may exhibit and the displacement analysis which should be carried out.  相似文献   

16.
Two in-flight shear wave velocity measurement systems were developed to perform the subsurface exploration of shear wave velocity in a centrifuge model. The bender elements test and the pre-shaking test used in the study provided reliable and consistent shear wave velocity profiles along the model depth before and after shaking in the centrifuge shaking table tests. In addition, the use of the bender elements measurement system particularly developed here allowed continuous examination of the evolution of shear wave velocity not only during and after the shaking periods in the small shaking events but also during the dissipation period of excess pore water pressure after liquefaction in the large shaking events. The test results showed that the shear wave velocity at different values of excess pore water pressure ratio varied as the effective mean stress to the power of 0.27, to a first approximation. Consequently, a relationship between the shear wave velocity evolution ratio and the excess pore water pressure ratio is proposed to evaluate the changes in shear wave velocity due to excess pore water generation and dissipation during shaking events. This relation will assist engineers in determining the shear stiffness reduction ratio at various ru levels when a sand deposit is subjected to different levels of earthquake shaking.  相似文献   

17.
Liquefaction of saturated loose sand is a major cause of extensive damage to buildings and infrastructures during large earthquakes. A better understanding of the behaviour of liquefied soil is becoming increasingly necessary to mitigate earthquake damage, and the fluid method has become an increasingly popular means to study the behaviour of liquefied soils. The purpose of this study is to determine the fluid characteristics of liquefied fine sand. In this paper, the apparent viscosity was measured as an index of fluid characteristics using the shaking table tests of pre-liquefaction behaviour of saturated fine sand at approximately 45 % relative density; the relationship of apparent viscosity and shear strain rate on liquefying fine sand was indicated as a power-law shear-thinning non-Newtonian fluid; and liquefying fine sand has the alternating behaviour of shear dilatancy and compressibility during cyclic loading. Additionally, a series of a monotonic axial compression loading tests in an undrained manner were performed to measure the shear stress and excess pore pressure ratio relationship on the post-liquefaction saturated fine sand at approximately 50 % relative density. The fluid characteristics of post-liquefaction fine sand exhibits rate dependence and can be described by a combined fluid model of time-independent and time-dependent power-law functions; the time-independent viscous resistance is not relevant to the excess pore pressure ratio; but the time-dependent frictional resistance is closely related to the excess pore pressure ratio. Furthermore, the results of the verification tests demonstrate that the proposed fluid model has good applicability for the fluid behaviour of the post-liquefaction fine sand.  相似文献   

18.
The mechanical response to cyclic loading of saturated cohesionless soils is usually investigated by means of effective stress method considering pore water pressure changes that lead to reduced strength and stiffness. On the other hand, the behavior of partially saturated sands is different from the behavior of saturated sand deposits. The development of negative pore water pressures in particular makes it difficult to estimate the behavior of partially saturated sands. The response of partially saturated sands, however, can be examined in a physically understandable manner by investigating their energy characteristics independently of pore pressure behavior. To establish a general framework for understanding the behavior of partially saturated sand, a total of 52 resonant column and dynamic torsional shear tests were conducted under undrained conditions. The effects of factors such as the amplitude of shear strain, relative density, saturation ratio and confining pressure on the dynamic characteristics of the sand and on energy dissipation were studied. The use of the energy concept in the evaluation of partially saturated soils is shown to be a promising method for the evaluation of the cyclic behavior of partially saturated sands.  相似文献   

19.
Seismicity is known to contribute to landscape denudation through its role in earthquake‐triggered slope failure; but little is known about how the intensity of seismic ground motions, and therefore triggering of slope failures, may change through time. Topography influences the intensity of seismic shaking – generally steep slopes amplify shaking more than flatter slopes – and because glacial erosion typically steepens and enlarges slopes, glaciation may increase the intensity of seismic shaking of some landforms. However, the effect of this may be limited until after glaciers retreat because valley ice or ice‐caps may damp seismic ground motions. Two‐dimensional numerical models (FLAC 6.0) were used to explore how edifice shape, rock stiffness and various levels of ice inundation affect edifice shaking intensity. The modelling confirmed that earthquake shaking is enhanced with steeper topography and at ridge crests but it showed for the first time that total inundation by ice may reduce shaking intensity at hill crests to about 20–50% of that experienced when no ice is present. The effect is diminished to about 80–95% if glacier ice level reduces to half of the mountain slope height. In general, ice cover reduced shaking most for the steepest‐sided edifices, for wave frequencies higher than 3 Hz, and when ice was thickest and the rock had shear stiffness well in excess of the stiffness of ice. If rock stiffness is low and shear‐wave velocity is similar to that of ice, the presence of ice may amplify the shaking of rock protruding above the ice surface. The modelling supports the idea that topographic amplification of earthquake shaking increases as a result of glacial erosion and deglaciation. It is possible that the effect of this is sufficient to have influenced the distribution of post‐glacial slope failures in glaciated seismically active areas. Copyright © 2012 John Wiley & Sons, Ltd.  相似文献   

20.
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。  相似文献   

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