广西宁明膨胀土胀缩活动带特征及滑坡破坏模式研究

通过对南(宁)友(谊关)高速公路宁明下第三系湖相风化泥岩及其残积土路堑边坡的系统地质调查、现场监测,对比研究了膨胀土自然边坡和路堑边坡胀缩活动带的含水率、地温、收缩系数及50 kPa下膨胀量随深度的变化特征,结合对边坡胀缩裂隙与滑坡体形态要素的相关性分析,提出了胀缩活动带滑坡的半定量破坏模式,为有效进行工程处治提供了依据。     

Impact of the wetting process on the hydro-mechanical behavior of unsaturated residual soil from flysch rock mass: preliminary results

Slope instabilities in the form of shallow and deep-seated landslides in flysch formations throughout Europe typically occur after prolonged periods of heavy rainfall. The Rječina River Valley, Croatia, is characterized by the presence of flysch material in the lower part of the Valley, where numerous historical and recent landslides have occurred. The weathering process and climate conditions result in a complex engineering geological profile of flysch slopes in the Valley, with unsaturated residual soil covering the slopes. To investigate the behavior of residual soil existing on the flysch slope under increasing water content due to the rainfall infiltration process, undisturbed soil samples collected at natural water content were tested in the modified direct shear apparatus. Under imposed stress conditions, samples of low hydraulic conductivity were subjected to a prolonged wetting process simulating the rainfall infiltration process in the field. The obtained results suggest that a gradual decrease of matric suction and an increase of water content resulted in an increase of displacement rates under constant shear stress, which was interpreted as a failure of samples in partially saturated conditions. A unique shear strength envelope expressed in terms of Bishop’s effective stress equation was found to be able to predict stress conditions at the slip surface at the time of failure, while the relationship between measured matric suction and water content closely matched with the main wetting curve. Although the testing results did not point out any special characteristics of residual soil from flysch rock mass behavior, the data about hydro-mechanical behavior of unsaturated residual soil from flysch rock mass, as well as similar fine-grained soils, are very rare and presented results would be valuable for further research. The presented testing procedure and obtained results are useful for studies of rainfall-induced landslides triggered in fine-grained soil materials in zones above the phreatic line, such as shallow landslides occurring in natural flysch slopes or in physical landslide models built in laboratories.

     

全风化灰绿色及红色泥岩物理力学性质对比研究

 灰绿色、红色泥岩在干旱或半干旱气候条件下形成,富含黏土矿物,遇水后物理力学性质发生显著变化,对工程建设的安全有重要影响,对其物理力学特性开展研究在地质灾害防治和工程设计施工中都具有重要意义。不同泥岩具有不同的物理力学性质,为进一步研究其差异,对甘肃省天水秦州区西河乡灰绿色泥岩以及天水花南村滑坡(310国道K1428+200段)滑带处红色泥岩进行了基本土工试验、矿物成分分析、易溶盐成分分析以及高含水率下的直接剪切试验。研究发现灰绿色泥岩级配更好,且含有较多的黏土矿物,而红色泥岩则含有较多的石英及原生矿物,二者的黏土矿物都以伊利石为主,高岭石次之,蒙脱石含量较少。2种泥岩遇水后都溶解出较多的Na+,K+, 以及少量的Ca2+,使土体颗粒水膜增厚,带电分子间的引力减弱,黏结力降低,并使矿物更易遭受破坏,灰绿色泥岩溶于水后的易溶盐总量相对较多。在高含水率情况下,2种泥岩的抗剪强度参数都随含水率及干密度发生变化,灰绿色泥岩的抗剪性能明显优于红色泥岩。当含水率达到25%时,红色泥岩抗剪强度较绿色泥岩显著降低,含水率超过30%后,二者都基本丧失抗剪能力。     

Earthquake-triggered landslides by the 1718 Tongwei earthquake in Gansu Province,northwest China

The 1718 great Tongwei earthquake in northwest China caused more than 300 large-scale landslides near the epicenter resulting in more than 70,000 deaths. Although previous studies agree that the earthquake-induced landslides in the area are loess-landslides, which slid along ancient terrain surfaces, there is a dearth of evidence to unravel the actual failure mechanisms of these widely-documented events. To clarify their characteristics and mechanisms, the landslides in Pan’an Town, located in Gansu Province, China were rigorously investigated. The field surveys revealed that the landslides occurred in an area comprising loess deposits of several tens of meters underlain by a basal mudstone layer. It was also revealed that instability in the area is strongly influenced by a river valley with large erosion bank slopes, as well as steep mudstone slopes, which are well developed. The majority of the landslides triggered by the Tongwei earthquake were loess-mudstone composite landslides, with the sliding surface in the deep mudstone. Three huge landslides on the northern mountain located at the river bend of Pan’an Town with a total volume of about 6.06 × 10⁸ m³ are the main mass movements during the 1718 catastrophe. In addition, by taking the typical landslide named the Weijiawan landslide as a case study, the internal structure of the earthquake-triggered landslides and their stability were studied. The new findings not only aided the unraveling of the failure mechanisms but also provided insights and knowledge on early recognition of earthquake-triggered landslides in northwest China towns, especially in the surrounding valley, which shares similar geological conditions with landslides studied in this paper.     

边坡滑动预测的有限元分析

滑坡发生时间的有效预测,将有助于减少滑坡灾害所造成的损失,因此,如何有效预测滑坡的发生时间是坡地地质灾害防灾减灾工作中极为重要的一环。通过非饱和土坡的算例,并结合试验槽试验的试验结果,探讨将边坡稳定分析应用于滑坡发生的时机预测可能面临的问题。结果表明:稳定分析所预测的边坡破坏时间与非饱和土的参数、初始基质吸力场的分布和非饱和土的强度准则关系密切。因此,仍需进一步研究和讨论,以期能更合理的应用稳定分析方法的结果,并作为边坡灾害预警的理论依据。     

Earthquake-induced landslides: Distribution,motion and mechanisms

The objective of this paper is to clarify the factors that resulted in many landslides during the 2011 off the Pacific Coast of Tohoku Earthquake. The geology of the Tohoku district, the seismic motion of the main shock and the precipitation around the time of the earthquake are described. As one of the characteristic phenomena observed around Shirakawa city in Fukushima prefecture and the mid-eastern part of Tochigi prefecture, many of the slopes were characterized by a high distribution of sensitive volcanic cohesive soils. The estimated PGA and PGV around the areas were therefore larger, which might have promoted the softening of the sensitive soils.Although there had been little precipitation before the main shock, the landslides occurred mostly in the slopes containing the volcanic cohesive soils with higher water content. The influences of the ground water as well as other factors on the seismic slope stability are discussed in each of the following case studies. In order to clarify the mechanism of each landslide, the study focused on three typical landslides which occurred in the affected areas, i.e., the Hanokidaira, Okanouchi and Kami-kashiwazaki landslides. Detailed surveying with a laser profiler (LP) was carried out at the Hanokidaira and Okanouchi landslides to enable the topography of each slope before and after the main shock to be accurately grasped. Analytical examinations for the sliding mechanisms in each slope from an engineering point of view are made based on the numerical analyses with the actual soil properties observed in the laboratory tests. According to the results obtained from the cyclic direct and triaxial tests using the undisturbed specimens of the clayey loams sampled at the slip surfaces in each landslide, the shear strength can be reduced under cyclic loading and may eventually make the materials behave as those of high-mobility. Strength reduction is believed to be caused by the destruction of the clay particle structures originated from the sedimentation. Since the duration of the main shock exceeded three minutes, the slopes were subjected to the strong motion for a very long time. The sensitive cohesive soils resulted in a state with high mobility, which might have been the reason for the long distances traveled by the debris.     

兰永一级公路顺层滑坡抗剪强度参数确定及应用

兰永一级公路工程修建过程中在路堑边坡开挖时形成了顺层边坡,以K23+520处的大型顺层滑坡最为典型。由于岩土体抗剪强度参数在边坡稳定性分析和加固设计中不可或缺,为了更好地实现其余类似边坡的加固设计和稳定性分析,以K23+520处的滑坡为研究对象,提出含有软弱夹层的顺层滑坡结构面上抗剪强度参数的确定方法:对已知一个滑动面位置的滑移–拉裂破坏模式下的顺层滑坡,通过结合顺层滑坡失稳条件(临界高度、局部稳定系数)及变形破坏特征对满足刚体滑移模型下的多组强度参数进行逐步修正,得到了满足工程应用要求的强度参数取值,并将结果用于类似边坡的加固设计和稳定分析。方法不仅适合兰永一级公路K23+520处顺层滑坡结构面上抗剪强度参数的确定,还适用于类似滑坡工程强度参数的确定,具有一定的工程实用价值。     

驷马山分洪道膨胀土特性及其滑坡治理

本文以安徽省滁河驷马山分洪道膨胀土为研究对象,对分洪道不同河段的膨胀土边坡进行取样,开展了膨胀土在不同工况条件下的物理力学试验。通过室内试验和现场监测,获得了膨胀土膨缩变形与土体抗剪强度变化等特征参数。经过对分洪道边坡滑动形成机理和变化规律的调查和分析,提出了膨胀土边坡稳定计算中强度取值的建议和边坡滑动的治理措施,为分洪道扩大工程及其同类工程设计提供了地质依据。     

延边地区公路沿线膨胀性软岩的发现与试验研究

延边地区公路沿线滑坡调查中，发现了一种工程性质不良、易于导致滑坡地质灾害的膨胀性软岩，通过对其物质组成、水理、力学和物化性质的一系列试验研究(包括蠕变、直剪、三轴压缩、膨胀、崩解、X光衍射和电镜扫描试验等)，认为该软岩属强膨胀性软岩，粘粒矿物成分主要为蒙脱石和伊、蒙混层矿物。通过研究它们的成因、分布和成灾机理，提出了治理措施。     

Method of mitigating the surface erosion of a high-gradient mudstone slope in southwest Taiwan

Soft mudstone dominates the rock mass at southwest Taiwan. Mudstone slakes significantly when it meets water due to a short diagenetic period and poor cementation. Gulleys are visible on the surface of mudstone slopes after rainfall. The low slaking durability resistance of the mudstone causes not only geographical badland but also erosion problems on the highway slopes in the mudstone area. An effective countermeasure for protecting the mudstone slope must contribute to a reduction in surface erosion; facilitate drainage from the slope surface during rainfall; and incorporate a high-strength structure to fight against swelling stress, preserve vegetation, and contribute to slope stabilization. In this study, a new slope erosion countermeasure, the soil-tyre-vegetation method (STV), was applied to an excavated mudstone slope in southwest Taiwan. STV utilizes waste tyres, H-beams, and geotextile. Waste tyres are good for preserving the soil for vegetation on mudstone slopes, mitigating slope erosion. The H-beams support the weight of the vegetation and the soil-filled tyres. The geotextile prevents the loss of fine-grain soil and guarantees drainage from the slope during heavy rainfall. The experimental results for a mudstone slope with a slope angle of 45° showed that STV protected the mudstone slope and improved the condition of the vegetation on it.     

红层软岩顺层滑坡临滑预报的强度控制方法*

 我国西部地区侏罗系、白垩系、第三系红层软岩广泛分布,红层软岩岩体强度低、抗风化能力弱、水敏感性强、工程地质性质较差、滑坡灾害严重。红层软岩顺层滑坡赋存的地质环境条件是形成滑坡的控制性因素,岩体强度特征决定滑坡的力学变形机制。不同变形、破坏条件影响红层软岩滑坡运移机制与特征。红层软岩岩体强度各向异性规律性强,岩层层面在各种地质营力的长期作用下逐步演化为滑动面。在研究红层软岩不同破坏条件下岩体强度特征与岩层层面抗剪强度变化规律,分析红层软岩滑坡的蠕动变形与滑动面形成机制的基础上,通过对典型红层软岩顺层滑坡临滑预报实例分析,提出了一种红层软岩顺层滑坡临滑预报的强度控制方法。     

香港的斜坡灾害及防治

香港城区的人造斜坡上每年雨季都要发生滑坡、落石等地质灾害,危及市民的生命财产安全。文中以滑坡为例具体分析了斜坡灾害的特征,探讨了滑坡体的移动特征以及滑坡与降雨量的关系,介绍了香港政府推动实施的斜坡减灾计划及其效果。     

库水位下降对滑坡稳定性的影响

三峡水库2003年蓄水后，滑坡将可能成为三峡库区最严重的地质灾害之一，库水位下降和暴雨是导致滑坡的主要因素。根据三峡库水位调控方案考虑库区极端暴雨情况，利用有限元模拟库水位在175～145m波动和降雨时红石包滑坡Ⅲ的暂态渗流场，将计算得到的暂态孔隙水压力分布用于滑坡的极限平衡分析，并考虑基吸力对非饱和土抗剪强度的影响。探讨不同降雨速度、降雨条件对滑坡稳定性的影响。研究表明：库水位下降对滑坡稳定性的影响受控于滑坡土的入渗能力和滑坡结构形态，当暴雨强度为300mm／d时，红石包滑坡Ⅲ的临界降速1m／d。其成果将为库区滑坡治理提供科学依据。     

Evaluation of Run-Out Distances of Slope Failures During 2004 Niigata-Ken Chuetsu Earthquake

During 2004 Niigata-ken Chuetsu Earthquake in Japan, a large number of landslides occurred on natural slopes, especially at the hillsides in the region of Yamakoshi. In many of the large slides, the debris has travelled through a fairly long distance, aggravating the disaster caused by the landslides. In recognizing its importance, case studies were undertaken on the run-out distance of the landslides at several sites at Higashi-Takezawa, Mushigame and Naraki. Case studies are also undertaken for slope failures involving the man-made deposits behind retaining walls surrounding the residential hill at Takamachi-Danchi in Nagaoka. In the first section of the present study, a simple analytical method is introduced based on the energy principle, in which the residual strength is taken up as a sole parameter to determine the run-out distance combined with the geometry of the landslides. The slope failure is herein assumed to consist of two phases, sliding and spreading, and the sliding distance is defined as the length of a slope on which the mass of soils slides down, and the run-out distance is determined as the one on a gentle slope or flat plane on which the phase of spreading occurs. Soil samples were retrieved from the sites of landslide, and laboratory triaxial tests are conducted on unsaturated soil samples with varying water contents. The residual shear strength thus obtained was used as an input parameter in the simple analysis to forecast the run-out distance. The outcome of the present study is presented in a form of simple charts in which the run-out distance is expressed as function of relevant geometrical parameters and the residual shear strength of soils involved in the landslide.     

某滑坡稳定性分析与评价

以花栗树包滑坡Ⅲ的工程实践为例,通过整理相关勘查资料、岩土试验等资料,分析了该滑坡的基本情况、滑坡体的物质组成、结构特征及物理力学性质,探讨了滑坡的破坏机理,用极限平衡法对滑坡体的稳定性进行了计算,并对其在不同工况条件下的稳定性进行了分析、评价与预测。     

Application of computerized tomographic scanning to the study of water-induced weakening of mudstone

Water generally plays a harmful role in the stability of mudstone and has induced many geological disasters in mudrock strata. To visually examine water-induced deterioration of mudstone, X-ray computerized tomographic scanning was used to detect the real-time interaction between mudstone and water. This facilitated real-time visual observations of the evolving characteristics of water-induced cracks within the samples. According to these experimental findings, assisted with scanning electron microscopy and X-ray diffraction, the water-weakening mechanisms of mudstone can be divided into the following steps: (1) micro-sized discontinuities provide an initial path for water to invade the rock; (2) the incursive water induces volumetric swelling of clay minerals and dissolution of carbonate; and (3) these effects drive the propagation and connection of cracks. This understanding of the processes of degradation provides a visual evidence for the assessment of mudrock performance with respect to the stability of landslides, debris flows, and susceptibility of subsidence in mudstone strata.     

The 1988 Nanka landslide,Anambra state,Nigeria

In 1988 a major landslide which required the evacuation of more than 50 families occurred in the little town of Nanka in Anambra State, Nigeria. Investigation revealed that the landslides were caused by an overconsolidated, very highly plastic mudstone layer (PI=67) which probably contained quantities of montmorillonite clay. Peak strength values of remolded samples of the mudstone measured in the ordinary shear box test differed from those of non-remolded (intact) samples only in showing zero cohesion. These values probably represent the strength of the mudstone in its normally consolidated condition. Stability analysis indicated that the major slide approximated more to a sliding block than to a circular failure with the mudstone layer as the base. It also showed that the peak strength at which the major slide occurred probably represents the strength of the mudstone in its fully softened or critical state, while the residual strength at which the minor slides occurred probably represents the strength at large displacements when perhaps the clay particles had become highly oriented in the direction of movement. In the present study, for the first time, the landslides in the highly unstable Nanka area are explained by the presence of active clays.     

Slope failure mechanisms in dipping interbedded sandstone and mudstone revealed by model testing and distinct-element analysis

Slopes with interbedded rock layers are widely distributed around the world and have experienced numerous landslide disasters. This study used physical model tests and the distinct-element method to identify the failure mechanisms of slopes with interbedded sandstone and mudstone. First, physical model tests were designed and carried out to investigate the effects of river incision and mudstone wetting-softening on the deformation and failure modes of such slopes. Subsequently, a distinct-element simulation was conducted to back-analyze the physical model tests and to investigate the effects of the boundary conditions and joint sets on the slope failure mechanisms. The physical model tests reveal that river incision alone may not be sufficient to cause a landslide. However, this situation may change instantaneously depending on the exposure and wetting-softening of deep mudstone layers. The results of the physical model tests were then used to verify the results of the distinct-element simulation. The simulated displacement distribution and failure mode agreed well with the measurements and observations from the physical model tests. The numerical simulation indicated that numerous tensile micro-cracks form in the upper part of the slope due to river incision, and several micro-cracks may develop into macro-cracks as a result of mudstone wetting-softening. In addition, a preliminary numerical parametric study indicates that the slope failure mode does not change when the left boundary condition varies from free to roller conditions, and the layers are continuous instead of discontinuous. However, the simulation shows that penetrative tension cracks are less likely to form in the river incision process of a slope without joints. In this case, landslides do not tend to occur because it is difficult for rainfall to seep into the slope and converge to mudstone layers, which are prone to softening in water.     

贵阳地区工程滑坡的成因调查与分析

通过对贵阳地区多起工程滑坡产生的原因进行研究分析发现，其广泛分布的三迭系基岩、第四系堆积物中的一些组成，泥页岩、残坡积红黏土以及残坡积黏性土等，在水及人类工程活动等因素的作用下极易发生工程滑坡，进而掌握了工程滑坡的机理，以减少或避免滑坡的发生。     

四川都江堰白依庵泥岩矿高陡边坡环境治理和生态修复

矿山创面高陡边坡是矿山地质环境治理与生态修复的难点。该文选取四川都江堰白依庵泥岩矿高陡边坡为研究对象,通过野外矿山地质环境详细调查,认为边坡失稳、滑坡灾害和创面边坡大面积裸露制约白依庵泥岩矿安全生产和环境保护的主要问题。识别出2处创面边坡滑坡,其中Ⅰ#滑坡堆积区岩土体处于欠稳定-稳定状态,Ⅱ#滑坡当前经历过整体失稳滑移,目前处于基本稳定-欠稳定状态。基于生态自循环理念,在创面边坡构建合理的土壤结构,以生态修复措施协助自然生态恢复。将创面边坡分为破碎岩面、完整岩面和滑坡面三种类型,根据泥岩面的特点分布设计生态修复方案和工艺流程。