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1.
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. 相似文献
2.
Fanyu Zhang Jianbing Peng Xiugang Wu Fazhen Pan Yao Jiang Chao Kang Weijiang Wu Wenguo Ma 《地球表面变化过程与地形》2021,46(10):2060-2078
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
3.
Tomomi Terajima Ei‐ichiro Miyahira Hiroyuki Miyajima Hirotaka Ochiai Katsumi Hattori 《水文研究》2014,28(23):5711-5724
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
4.
Fluid‐filled granular soils experience changes in total stress because of earth and oceanic tides, earthquakes, erosion, sedimentation, and changes in atmospheric pressure. The pore volume may deform in response to the changes in stress and this may lead to changes in pore fluid pressure. The transient fluid flow can therefore be induced by the gradient in excess pressure in a fluid‐saturated porous medium. This work demonstrates the use of stochastic methodology in prediction of induced one‐dimensional field‐scale groundwater flow through a heterogeneous aquifer. A closed‐form of mean groundwater flux is developed to quantify the induced field‐scale mean behavior of groundwater flow and analyze the impacts of the spatial correlation length scale of log hydraulic conductivity and the pore compressibility. The findings provided here could be useful for the rational planning and management of groundwater resources in aquifers that contain lenses with large vertical aquifer matrix compressibility values. 相似文献
5.
Evolution of the shear wave velocity during shaking modeled in centrifuge shaking table tests 总被引：2，自引：1，他引：1
Chung-Jung Lee Chung-Ru Wang Yui-Chen Wei Wen-Yi Hung 《Bulletin of Earthquake Engineering》2012,10(2):401-420
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
6.
An alternative Boussinesq equation considering the effect of hysteresis on coastal groundwater waves 
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下载免费PDF全文 This paper presents an alternative Boussinesq equation considering hysteresis effect via a third‐order derivative term. By introducing an improved moisture–pressure retention function, this equation describes, with reasonable precision, groundwater propagation in coastal aquifers subject to Dirichlet boundary condition of different oscillation frequencies. Test results confirmed that it is necessary to consider horizontal and vertical flows in unsaturated zone, because of their variable influences on hysteresis. Hysteresis in unsaturated zone can affect the water table wave number of groundwater wave motion, such as wave damping rate and phase lag. Oscillations with different periods exert different hysteresis effect on wave propagation. Truncation/shrinkage of unsaturated zones also affects the strength of hysteresis. These impacts can be reflected in the alternative Boussinesq equation by adjusting the parameter representing the variation rate of moisture associated with pressure change, as opposed to traditional computationally expensive hysteresis algorithms. The present Boussinesq equation is simple to use and can provide feasible basis for future coupling of groundwater and surface water models. Copyright © 2016 John Wiley & Sons, Ltd. 相似文献
7.
A series of 2-D centrifuge modeling tests with an in-flight shaker were carried out in order to model both the deformation characteristics of backfill and the seismic responses of caisson-type walls embedded in soils with various permeabilities. The rotational and translational modes were found to be in phase or various degrees out of phase with each other for quay walls embedded in soils with varying permeabilities. The alternative pumping and suction processes in excess pore water pressure that are caused by a wall's vibrations increase the level of damage because large amounts of backfill are forcedly leaked into the sea. The test results show that the rotational mode makes the dominant contribution to the changes in excess pore water pressure and in the earth pressure in the deep layers of soil, but the translational mode makes the dominant contribution to these pressures in the shallow layers. The average shear wave velocities were found to decrease rapidly to values as low as 1/8th of the velocity measured at the beginning of shaking. 相似文献
8.
Stresses and excess pore pressure induced in saturated poroelastic halfspace by moving line load 总被引：2，自引：0，他引：2
This paper examines stresses and excess pore fluid pressure that are induced in a saturated poroelastic soil of halfspace extent by a concentrated line load. The line load is moving at a constant velocity along the surface of the poroelastic halfspace. The governing equations for the proposed analysis are based on the Biot's theory of dynamics in saturated poroelastic soils. The governing partial differential equations are solved using Fourier transforms. The solutions for the stresses and excess pore pressure are expressed in the forms of inverse Fourier transforms. The numerical results are obtained by performing the numerical inversion of the transform integrals. A parametric study is presented to illustrate the influences of the velocity of moving load and the poroelastic material parameters on the stresses and excess pore pressure. At a high velocity, the maximum values of the stresses in a poroelastic halfspace are smaller than those in an elastic solid, whilst at a low velocity the stresses in a poroelastic halfspace are larger than those in an elastic halfspace. The potential of diffusivity has an important influence on the stresses and excess pore pressure. 相似文献
9.
Motion of a large rock mass down a slope can either take the form of a catastrophic landslide, or can exhibit self-stabilization, where the mass arrests on the slope, after moving only a short distance. In order to study the parameters that control the stability of the sliding process, a thermo-poro-elastic model is investigated both numerically and analytically. This model assumes that the physics controlling sliding stability is dominated by coupling between frictional heating, thermal pressurization and sliding velocity: A temperature increase due to frictional heating causes thermal pressurization within a fluid-saturated shear zone. The pressure rise leads to reduction of frictional resistance, which in turns leads to higher sliding velocities. Results demonstrate that the permeability of the sliding mass is an important factor in controlling the sliding stability: Low permeabilities lead to catastrophic landslides, by allowing high pore pressure to develop and friction to be reduced. In contrast, high permeabilities lead to rapid arrest by promoting pore pressure diffusion. A pore pressure – velocity phase plane is described, divided by a separatrix distinguishing between catastrophic and arrested sliding. In this phase plane minute changes in permeability dictate a bifurcation in the dynamics of landslides. A sensitivity study reveals that various geometrical and mechanical parameters can control the sliding process dynamics in a similar manner. It is hypothesized that a third sliding regime observed in nature, creep sliding, may be generated by a sequence of arrested events, where the number of arrested events/unit time dictates the apparent creep velocity. 相似文献
10.
Seasonal transition of hydrological processes in a slow‐moving landslide in a snowy region 下载免费PDF全文
下载免费PDF全文 Hikaru Osawa Yuki Matsushi Sumio Matsuura Takashi Okamoto Tatsuya Shibasaki Hiroyuki Hirashima 《水文研究》2018,32(17):2695-2707
A comprehensive understanding of seasonal hydrological dynamics is required to describe the influence of pore‐water pressure on the stability of landslides in snowy regions. This study reports on the results of continuous meteorological and hydrological observations over 2 years on a landslide body comprising Neogene sedimentary rocks in northern Japan, where a thick (3–5 m) seasonal snowpack covers the land surface. Monitoring of the volumetric water content in shallow unsaturated zones (<0.8 m depth) and pore‐water pressure in saturated bedrock at depths of 2.0 and 5.2 m revealed clear seasonality in hydrological responses to rainfall and meltwater supply. During snow‐free periods, both the shallow soil moisture and deep pore‐water pressure responded rapidly to intense rainwater infiltration. In contrast, during snowmelt, the deep pore pressure fluctuated in accordance with the daily cycle of meltwater input, without notable changes in shallow moisture conditions. During occasional foehn events that cause intense snow melting in midwinter, meltwater flows preferentially through the layered snowpack, converging to produce a localized water supply at the ground surface. This episodically triggers a significant rise in pore‐water pressure. The seasonal differences in hydrological responses were characterized by a set of newly proposed indices for the magnitude and quickness of increases in the pressure head near the sliding surface. Under snow‐covered conditions, the magnitude of the pressure increase tends to be suppressed, probably owing to a reduction in infiltration caused by a seasonal decrease in the permeability of surface soils, and effective pore‐water drainage through the highly conductive colluvial layer. Deep groundwater flow within bedrock remained in a steady upwelling state, enhanced by increasing moisture in shallow soils under snow cover, reflecting the convergence of subsurface water from surrounding hillslopes. 相似文献
11.
Groundwater—Surface waters interactions at slope and catchment scales: implications for landsliding in clay‐rich slopes 下载免费PDF全文
下载免费PDF全文 Vincent Marc Catherine Bertrand Jean‐Philippe Malet Nicolas Carry Roland Simler Federico Cervi 《水文研究》2017,31(2):364-381
Understanding water infiltration and transfer in soft‐clay shales slopes is an important scientific issue, especially for landsliding. Geochemical investigations are carried out at the Super‐Sauze and Draix‐Laval landslides, both developed in the Callovo‐Oxfordian black marls, with the objective to define the origin of the groundwater. In situ investigations, soil leaching experiments and geochemical modeling are combined to identify the boundaries of the hydrological systems. At Super‐Sauze, the observations indicate that an external water flow occurs in the upper part of the landslide at the contact between the weathered black marls and the overlying formations, or at the landslide basement through a fault network. Such external origin of water is not observed at the local scale of the Draix‐Laval landslide but is detected at the catchment scale with the influence of deep waters in the streamwater quality of low river flows. Hydrogeological conceptual models are proposed emphasizing the role of the interactions between local (slope) and regional (catchment) flow systems. The observations suggest that this situation is a common case in the Alpine area. Expected consequences of the regional flows on slope stability are discussed in term of rise of pore water pressures and physicochemical weathering of the clay shales. 相似文献
12.
The objective of this work is to analyse the storage–flux hysteretic behaviour of a simplified model for subsurface flow processes. The subsurface flow dynamics is analysed by means of a model based on the kinematic wave assumptions and by using a width weighting/depth averaging scheme which allows to map the three-dimensional soil mantle into a one-dimensional profile. Continuity and a kinematic form of Darcy’s law lead to a hillslope-storage kinematic wave equation for subsurface flow, solvable with the method of characteristics. Adopting a second order polynomial function to describe the bedrock slope and an exponential function to describe the variation of the width of the hillslope with hillslope distance, we derive general solutions to the hillslope-storage kinematic wave equations, applicable to a wide range of hillslopes. These solutions provide a physical basis for deriving two geometric parameters α and ψ which define the hydrological similarity between hillslopes with respect to their characteristic response and hysteresis. The hysteresis η, quantified by the area of the hysteretic dimensionless loop, has been therefore computed for a range of values of parameters α and ψ. Slopes exhibit generally clockwise hysteretic loop in the flux-storage plot, with higher groundwater mean volume for given discharge on rising limb than at same discharge on falling limb. It has been found that hysteresis increases with decreasing α and ψ, i.e. with increasing convergence (for the shape) and concavity (for the profile), and vice versa. For relatively large values of α and ψ the hysteresis may take a complex pattern, with combination of clockwise to anticlockwise loop cycles. Application of the theory to three hillslopes in the Eastern Italian Alps provides an opportunity to examine how natural topographies are represented by the two hillslope hydrological similarity parameters. 相似文献
13.
14.
A.J. Merritt J.E. Chambers W. Murphy P.B. Wilkinson L.J. West S. Uhlemann P.I. Meldrum D. Gunn 《地球表面变化过程与地形》2018,43(6):1321-1334
A common factor in landslide activation (or reactivation) is subsurface moisture and associated pore pressure variations linked to rainfall. Monitoring of these subsurface hydrogeological processes is necessary to improve our understanding of water‐induced landslide activation. Geophysical approaches, electrical methods in particular, are increasingly being applied to landslide monitoring because they provide non‐invasive spatial information in heterogeneous subsurface environments that can be difficult to characterise using surface observations or intrusive sampling alone. Electrical techniques are sensitive to changing subsurface moisture conditions, and have proven to be a useful tool for investigating the hydrogeology of natural and engineered slopes. The objectives of this investigation were to further develop electrical resistance monitoring for slope stability assessment, and to validate the approach at an intermittently‐active UK landslide system to advance the understanding of complex landslide activation mechanisms. A long‐term transfer resistance dataset was collected from a grid of electrodes to allow spatial monitoring of the landslide. These data were interpreted using a synthesis of rainfall, temperature, GPS and piezometric records. The resistance data were corrected for seasonal temperature variations and electrode movements were monitored, as these processes were shown to mask moisture related changes. Results reveal that resistance monitoring is sensitive to soil moisture accumulation, including changes in piezometric levels, and can be used to study the principal activation mechanism of slow‐moving shallow earthflows. Spatial monitoring using resistance maps was shown to be particularly valuable as it revealed the evolution of subsurface moisture distribution, in the lead up to landslide activation. Key benefits of this approach are that it provides a simple, rapid and non‐invasive means of spatially monitoring subsurface moisture dynamics linked to landslide activation at high‐temporal resolution. Crucially, it provides a means of monitoring subsurface hydraulic changes in the build‐up to slope failure, thereby contributing to early warning of landslide events. Copyright © 2018 John Wiley & Sons, Ltd. 相似文献
15.
V. de Montety V. Marc C. Emblanch J.‐P. Malet C. Bertrand O. Maquaire T.A. Bogaard 《地球表面变化过程与地形》2007,32(1):32-48
The Super‐Sauze mudslide is a persistently active slow‐moving landslide occurring in the black marl outcrops of the French South Alps. It has been intensively studied since the early 1990s. Geotechnical, geomorphological, geophysical and hydrological investigations have led to a better understanding of the processes governing the landslide motion. Water ?ows inside the system have been proven to have a major impact. To look closer at the processes involved and especially to gain a better idea of the origin and pathways of the waters, a hydrochemical study was carried out from May 2003 to May 2004. The groundwater was sampled during ?ve ?eld campaigns spread uniformly over the year. Groundwater from a network of boreholes was collected as well as spring waters from the fractured bedrock (in situ black marl) and from the moraine aquifer above the landslide. Results showed that the groundwater chemistry could not be fully explained by rainfall recharge or simple water–matrix equilibrium. A contribution of saline waters coming from the bottom of a thrust sheet overhanging the landslide was required to get the observed high mineralization. On a ?ow line, the hydrochemical evolution was related to both soil–matrix equilibrium and deep water sources coming up to the surface by means of major faults, the bedding planes and the schistosity. Hydrochemical anomalies made it possible to point out such contributions locally. It was shown that water chemistry and landslide activity were closely related. This hydrochemical investigation also enabled us to better de?ne the hydrosystem limits.Copyright © 2006 John Wiley & Sons, Ltd. 相似文献
16.
The internal deformation within debris flows holds essential information on dynamics and flow resistance of such mass-wasting processes. Systematic measurements of velocity profiles in real-scale debris flows are not yet available. Additionally, data on basal stresses of the solid and the fluid phase are rare. Here, we present and analyse measurements of vertical velocity profiles in two debris flows naturally occurring in the Gadria Creek, Italy. The method is based on cross-correlation of paired conductivity signals from an array of sensors installed on a fin-shaped wall located in the middle of the channel. Additionally, we measure normal stress and pore fluid pressure by two force plates with integrated pressure transducers. We find internal deformation throughout the flows. Only at the very front was some en-bloc movement observed. Velocity profiles varied from front to tail and between flows. For one debris flow, pore fluid pressure close to normal stress was measured, whereas the other flow was less liquefied. The median shear rates were mostly less than 5 s−1 and Savage numbers at the basal layer ranged from 0.01 to 1. Our results highlight the variable nature of debris flows and provide quantitative data on shear rate and basal stress distribution to help guide model development for hazard assessment and landscape evolution. © 2020 The Authors. Earth Surface Processes and Landforms published by John Wiley & Sons Ltd. 相似文献
17.
Uncertainty in applying the linear poroelasticity model to field situations as a result of periodic loading in heterogeneous aquifers 下载免费PDF全文
下载免费PDF全文 The solid Earth's surface frequently experience changes in total stresses as a result of periodic loading. When the fluid‐saturated porous media deform in response to changes in stress, the induced variations in pore volume affect the pore water pressure. The fluid flow therefore occurs in response to the gradient in the induced excess pore water pressure. This work aims at quantifying the spatial variability in excess pressure head produced by the periodic loading accounting for the variation of log hydraulic conductivity (lnK). It is important for the rational management of groundwater resources. A closed‐form expression is developed by the nonstationary spectral approach to analyse the influence of the statistical properties of lnK process, the hydraulic parameters, and the spatial position. The general stochastic framework outlined in this work provides a basis for assessing the impact of statistical properties of input aquifer parameters on the output variability (or uncertainty). Copyright © 2014 John Wiley & Sons, Ltd. 相似文献
18.
介观尺度孔隙流体流动是地震频段岩石表现出较强速度频散与衰减的主要作用.利用周期性层状孔隙介质模型,基于准静态孔弹性理论给出了模型中孔隙压力、孔隙流体相对运动速度以及固体骨架位移等物理量的数学解析表达式,同时利用Biot理论将其扩展至全频段条件下,克服了传统White模型中介质分界面处流体压力不连续的假设. 在此基础上对准静态与全频段下模型介质中孔隙压力、孔隙流体相对运动速度变化形式及其对弹性波传播特征的影响进行了讨论,为更有效理解介观尺度下流体流动耗散和频散机制提供物理依据.研究结果表明,低频条件下快纵波孔压在介质层内近于定值,慢纵波通过流体扩散改变总孔隙压力, 随频率的增加慢波所形成的流体扩散作用逐渐减弱致使介质中总孔压逐渐接近于快纵波孔压,在较高频率下孔压与应力的二次耦合作用使总孔压超过快纵波孔压.介质中孔隙流体相对运动速度与慢纵波形成的流体相对运动速度变化形式一致;随频率的增加孔隙流体逐渐从排水的弛豫状态过渡到非弛豫状态,其纵波速度-含水饱和度变化形式也从符合孔隙流体均匀分布模式过渡到斑块分布模式,同时介质在不同含水饱和度下的衰减峰值与慢纵波所形成的孔隙流体相对流动速度具有明显的相关性. 相似文献
19.
Recently, mode converted shear waves (C‐waves) have been shown to enable overpressure prediction in media where primary wave acquisition is inhibited by gas and fluid effects – C‐wave moveout is analysed and a long standing relationship between differential stress and primary‐wave (P‐wave) velocity is modified and employed. Though pore‐pressure prediction based on C‐waves is supported by empirical evidence from laboratory and field experiments, a theoretical justification has yet to be developed. In this research note, we provide a supporting algebra for the original relationship between pore pressure and C‐wave velocity. 相似文献
20.
《国际泥沙研究》2015,(3)
Landslide dams commonly form when mass earth or rock movements reach a river channel and cause a complete or partial blockage of the channel.Intense rainfalls can induce upstream flows along a sloping channel that significantly affect downstream landslide dams.If a series of landslide dams are collapsed by incoming mountain torrents(induced by intense rainfall),large debris flows can form in a very short period.Furthermore,the failure of these dams can amplify the magnitude and scale of debris flows in the flow direction.The catastrophic debris flows that occurred in Zhouqu County,China on 8 August 2010 were caused by intense rainfall and the upstream cascading failure of landslide dams along the gullies.Incorporating the role of outburst floods associated with the complete or partial failure of landslide dams is an interesting problem usually beyond the scope of analysis because of the inherent modeling complexity.To understand the cascading failure modes of a series of landslide dams,and the dynamic effect these failures have on the enlargement of debris flow scales,experimental tests are conducted in sloping channels mimicking field conditions,with the modeled landslide dams distributed along a sloping channel and crushed by different upstream flows.The failure modes of three different cascades of landslide dams fully or partially blocking a channel river are parametrically studied.This study illustrates that upstream flows can induce a cascading failure of the landslide dams along a channel.Overtopping is the primary failure mechanism,while piping and erosion can also induce failures for different constructed landslide dams.A cascading failure of landslide dams causes a gradually increasing flow velocity and discharge of the front flow,resulting in an increase in both diameter and percentage of the entrained coarse particles.Furthermore,large landslide blockages can act to enhance the efficiency of river incision,or conversely to induce aggradation of fluvial sediments,depending on the blockage factor of the landslide dams and upstream discharge. 相似文献