Geomorphology and engineering geology of a landslide in ultramafic rocks,Dawson City,Yukon

The Dawson City Landslide is located at the northern edge of Dawson City, Yukon and took place prior to 1740 years B.P. The landslide occurred at the contact between the metasedimentary rocks of the Yukon–Tanana Terrane and the overlying altered ultramafic rocks of the Slide Mountain Terrane. The main part of the failure comprises altered ultramafic rocks, which have a lower Geological Strength Index (rock mass quality) than the underlying metasedimentary sequence. Division of the study area into smaller structural domains identified discontinuity sets associated with faulting along the contact of the two lithological units. A kinematic analysis of the identified discontinuity sets suggests that a toppling failure mechanism may be feasible. Due to the highly fractured nature of the ultramafic rock mass, a circular failure controlled by the low strength of the rock mass is considered a potential mechanism for the Dawson City Landslide. Limit equilibrium and finite difference numerical modelling codes support a circular failure mechanism hypothesis. However, a combination of high pore water pressure (ru = 0.3), and seismic loading are required to produce a factor of safety < 1.0.The dominant trends of linear geomorphic features (tension cracks, trenches, anti-slope scarps, ridges) correspond to a discontinuity set recognised in the headscarp of the failure. Tension cracks exposing roots and split trees indicate recent movement of a small section of the headscarp that is potentially unstable. The downslope risk represented by this unstable block is difficult to assess due to the uncertainties related to entrainment of talus material and potential travel distance over the rough and irregular surface of the middle coarse debris material. The movement rate of this block should be monitored and the surrounding area routinely investigated for the development of other potentially unstable sections of the landslide. Sheared trenches, stretched roots and split trees suggest that the middle to lower section of the debris is currently moving.     

Stability analysis of the 2007 Chehalis lake landslide based on long-range terrestrial photogrammetry and airborne LiDAR data

On December 4th 2007, a 3-Mm³ landslide occurred along the northwestern shore of Chehalis Lake. The initiation zone is located at the intersection of the main valley slope and the northern sidewall of a prominent gully. The slope failure caused a displacement wave that ran up to 38 m on the opposite shore of the lake. The landslide is temporally associated with a rain-on-snow meteorological event which is thought to have triggered it. This paper describes the Chehalis Lake landslide and presents a comparison of discontinuity orientation datasets obtained using three techniques: field measurements, terrestrial photogrammetric 3D models and an airborne LiDAR digital elevation model to describe the orientation and characteristics of the five discontinuity sets present. The discontinuity orientation data are used to perform kinematic, surface wedge limit equilibrium and three-dimensional distinct element analyses. The kinematic and surface wedge analyses suggest that the location of the slope failure (intersection of the valley slope and a gully wall) has facilitated the development of the unstable rock mass which initiated as a planar sliding failure. Results from the three-dimensional distinct element analyses suggest that the presence, orientation and high persistence of a discontinuity set dipping obliquely to the slope were critical to the development of the landslide and led to a failure mechanism dominated by planar sliding. The three-dimensional distinct element modelling also suggests that the presence of a steeply dipping discontinuity set striking perpendicular to the slope and associated with a fault exerted a significant control on the volume and extent of the failed rock mass but not on the overall stability of the slope.     

A geotechnical investigation of the retrogressive Yaka Landslide and the debris flow threatening the town of Yaka (Isparta,SW Turkey)

In this study the factors affecting the retrogressive Yaka Landslide, its mechanism and the hazard of debris flow on the town of Yaka are investigated. In the landslide area, the first landslide was small and occurred in March 2006 on the lower part of the Alaard?ç Slope near the Gelendost District town of Yaka (Isparta, SW Turkey). The second, the Yaka Landslide, was large and occurred on 19 February 2007 in the soil-like marl on the central part of Alaard?ç Slope. The geometry of the failure surface was circular and the depth of the failure surface was about 3 m. Following the landslide, a 85,800 m³ of displaced material transformed to a debris flow. Then, the debris flow moved down the Eglence Valley, traveling a total distance of about 750 m. The town of Yaka is located 1,600 m downstream of Eglence Creek and hence poses a considerable risk of debris flow, should the creek be temporarily dammed as a result of further mass movement. Material from the debris accumulation has been deposited on the base of Eglence Valley and has formed a debris-dam lake behind a debris dam. Trees, agricultural areas, and weirs in the Eglence Creek have seen serious damage resulting from the debris flow. The slope angle, slope aspect and elevation of the area in this study were generated using a GIS-based digital elevation model (DEM). The stability of the Alaard?ç Slope was assessed using limit equilibrium analysis with undrained peak and residual shear strength parameters. In the stability analyses, laboratory test results performed on the soil-like marls were used. It was determined that the Alaard?ç Slope is found to be stable under dry conditions and unstable under completely saturated conditions. The Alaard?ç Slope and its vicinity is a paleolandslide area, and there the factor of safety for sliding was found to be about 1.0 under saturated conditions. The Alaard?ç Slope and the deposited earthen materials in Eglence Creek could easily be triggered into movement by any factors or combination of factors, such as prolonged or heavy rainfall, snowmelt or an earthquake. It was established that the depth of the debris flow initiated on the Yaka Landslide reached up to 8 m in Eglence Creek at the point it is 20 m wide. If this deposited material in Eglence Creek is set into motion, the canal that passes through Yaka, with its respective width and depth of 7 and 1.45 m, could not possibly discharge the flow. The destruction or spillover of this canal in Yaka could bring catastrophic loss to residents which are located within 3–5 m of the bank of the canal. Furthermore, if material present in the landslide source area slides and this displaced material puts pressure on the unstable deposited material in Eglence Creek, even more catastrophic loss would occur to the town of Yaka. In this study, it was determined that debris flows are still a major hazard to Yaka and its population of 3,000. The results provided in this study could help citizens, planners, and engineers to reduce losses caused by existing and future landslides and debris flow in rainfall and snowmelt conditions by means of prevention and mitigation.     

The 2007 Fox Creek landslide,Peace River Lowland,Alberta, Canada

Fox Creek is a small tributary of the Saddle River, a tributary of the Peace River in northwestern Alberta. It has several dormant landslides with degraded scarps and grabens. A new, reactivated landslide on the north bank of the Fox Creek occurred on 5 May 2007. The landslide formed two major sliding blocks. A rapid translational block slide, it mobilized 47 Mm³ of displaced materials, blocked the creek, and made a natural dam with a maximum height of 19 m at the tips of the displaced blocks. The rupture surfaces of the 2007 landslide were within the advance phase glaciolacustrine sediments. The residual friction angles are about 10° similar to those of the previous landslides in the Peace River Lowland. Precipitation and snow melt prior to the landslide are likely triggers of the 2007 Fox Creek landslide. The farmlands on the crest of the river valley and timber resources were impacted. The current landslide dam in Fox Creek does not have any evidence of seepage downstream; it may last for many years. Eventually, the creek will overtop and erode the dam. The same cycle of actions, landsliding, damming, and erosion will continue in the foreseeable future.     

The January 10, 1997 Pozzano landslide, Sorrento Peninsula, Italy

From 1997 to 1999, a huge number of slides, often turning into extremely rapid debris-earth flows, repeatedly affected the late Quaternary volcaniclastic deposits mantling the carbonate slopes of Campania region, Italy. The Sorrento Peninsula was the epicentral district of the 1997 regional slope-instability crisis. Some hundred shallow mass movements took place during January 1997 in this area. These were the last episode of a long series of slope failure events dating back to mid-18th century. Results from geological and geomorphologic surveys are presented. Landslide mechanism and triggering factors are analysed for the most important mass movement, which occurred during the January 9-11, 1997, regional event. On January 10, 1997, at about 8:15 PM, a rainfall-induced debris slide-debris flow occurred at Pozzano (province of Naples), mainly affecting the 79 AD pyroclastic products. Following a J-path, the landslide destroyed a private house and invaded the State Road no. 145. This event resulted in four deaths, 22 persons injured and road closure for about 2 months. There was less than 200 mm of rainfall in the 72-h period prior to the landslide, although intense precipitation had occurred during a preceding 4-month period. However, the slope failure event was not preceded by an extreme short-term antecedent rainfall, as already noticed in previous landslides of this type in Campania. Finally, following a preliminary geotechnical characterization of volcaniclastic soils, a slope-stability back analysis was carried out, which adopted the classical infinite slope scheme. This analysis gave further evidence of the role played by pore pressure in reducing the overall shear strength of pyroclastic soils.     

甘肃舟曲垭豁口滑坡复活机理及成因探讨

2019年7月19日18时许,甘肃舟曲县垭豁口滑坡复活,约3.92×106 m3的滑体顺坡而下,迅速流入岷江,堵塞河道,造成河道水位上升,江边公路中断,滑坡变形持续至8月中旬。基于野外勘察、遥感解译、钻孔勘探等方法获取了滑坡变形的基本特征,并开展了滑坡监测工作,并结合气象资料,探讨了该滑坡复活原因及启动机制。初步研究认为,该滑坡为降雨诱发。通过对滑坡变形历史进行梳理,结合滑带证据,滑坡复活机理可概括为:首先上部块体缓慢蠕变,降雨后发生塑性流滑;其次,因上部滑体堆积在滑坡中部,造成中部平台堆载,引发中部滑体变形;最终一滑而下,刮产连带下部滑体坠入河道。滑坡的上中下三部分滑体逐步被激活,最初缓慢变形,随后加速启动。滑坡变形模式为蠕滑—拉裂—流滑。对滑坡变形过程和机理的初步判断为滑坡灾害应急处置提供了科学依据。     

Landslide Hazard and Risk Assessment on the Northern Slope of Mt. Changbai, China

Landslide hazard and risk assessment on the northern slope of Mt. Changbai, a well-known tourist attraction near the North Korean-Chinese border, are assessed. This study is divided into two parts, namely, landslide hazard zonation and risk assessment. The 1992 Anbalagan and Singh method of landslide hazard zonation （LHZ） was modified and used in this area. In this way, an Associative Analysis Method was used in representative areas to get a measure for controlling factors （slope gradient, relative relief, vegetation, geology, discontinuity development, weak layer thickness and ground water）. For the membership degree of factor to slope failure, the middle range of limited values was used to calculate LHZ. Based on an estimation of the potential damage from slope failure, a reasonable risk assessment map was obtained using the relationship of potential damage and probable hazard to aid future planning and prediction and to avert loss of life.     

超孔隙水压诱发特大型近水平崩坡积层滑坡破坏研究

特大型近水平崩坡积层滑坡广泛发育于三峡库区重庆段万州城区及云阳地区。基于万州城区太白岩古滑坡以及云阳地区老药铺滑坡两个典型特大型近水平崩坡积层滑坡,分析了其结构特征及破坏特点;建立了强降雨作用下特大型近水平崩坡积层滑坡破坏的力学模型,解译了此类滑坡的破坏过程,并提出了滑带（面）超孔隙水压力是此类滑坡破坏的诱因。基于孔隙水压力与土体所处的应力状态的内在关系,推导了滑面处每个土条的孔隙水压力及水压力公式,并得出了考虑超孔隙水压力的滑坡稳定系数表达式。云阳地区老药铺滑坡算例表明,若将老药铺滑坡按zk5分为两个滑坡,两个滑坡的中心段是孔隙水压力值较高的区域;本文的孔隙水压力计算值略大于钻孔量测值,计算误差为5.8%～10%,原因在于滑面超孔隙水压力的消散;暴雨工况（含超孔隙水压力）下老药铺滑坡稳定系数为0.862,滑坡处于非稳定状态,并已发生破坏,验证了超孔隙水压力对滑坡体破坏的诱发作用;建议滑坡治理工程中应在按zk5分成的两个滑坡中间段打设排水孔,消除或降低滑面处的超孔隙水压力值,并结合滑坡周围及坡面的截排水工程以及封填裂隙治理老药铺滑坡。     

The Application of Artificial Neural Networks to Landslide Susceptibility Mapping at Janghung, Korea

The purpose of this study was to develop techniques for landslide susceptibility using artificial neural networks and then to apply these to the selected study area at Janghung in Korea. Landslide locations were identified from interpretation of satellite images and field survey data, and a spatial database of the topography, soil, forest, and land use. Thirteen landslide-related factors were extracted from the spatial database. These factors were then used with an artificial neural network to analyze landslide susceptibility. Each factor's weight was determined by the back-propagation training method. Five different training sets were applied to analyze and verify the effect of training. Then the landslide susceptibility indices were calculated using the back-propagation weights, and susceptibility maps were constructed from Geographic Information System (GIS) data for the five cases. Landslide locations were used to verify results of the landslide susceptibility maps and to compare them. The artificial neural network proved to be an effective tool for analyzing landslide susceptibility.     

Mechanism of the giant Seimareh Landslide,Iran, and the longevity of its landslide dams

Seimareh Landslide (SL) is globally recognized as one of the largest rock mass movements in the world. It is located along the border of Ilam and Lorestan provinces in southwest Iran, in the heart of the Zagros Mountain Range. There are controversial findings about the mechanism of the landslide formation. This field work study reviewed the possible mechanisms of failure and analyzed post-failure geomorphic features. Drainage pattern disturbance in the depositional region and consequent dammed lake formation are among the most significant characteristics of these features. Seimareh, Jaidar and Balmak are three large landslide-dammed lakes. The present study analyzed the processes responsible for the formation and erosion of the Jaidar and Seimareh Landslide dams using the available annual sedimentation and field measurements of the sediment deposited in these lakes. The results showed that the SL dam has been formed about 935 years after the landslide event. Detailed field investigations indicated a specific hydro-morphological condition in the landslide area. The results implied that the main causes of the failure were probably the particular hydro-morphological characteristic of the landslide source area together with the enormous eroding energy resulted from merging of two high-flow rivers which eroded the base of the southern flank of Kabir-kuh Mountain. However, the unusual size of the landslide suggests that an external factor, e.g., a huge earthquake, might have triggered the failure.     

甘肃通渭“9·14”常河滑坡成因机理

2019年9月14日11时,受多日降雨影响,甘肃省定西市通渭县常家河镇小庄村发生大规模黄土滑坡,体积约800万m³。滑坡造成部分农田、公路及阳坡大桥损毁,直接经济损失约2 347.2万元。在对滑坡现场进行大量地面调查的基础上,通过无人机航拍、现场测绘、走访调查和数值模拟等手段对滑坡的变形破坏特征进行了分析,并在此基础上探讨了其成因机制。结果表明:斜坡体是在震裂、蠕变、软化、水动力等多种条件下按照一定的先后顺序由稳态逐步演化至失稳;该滑坡的失稳演化过程和灾变机制可以概括为原始斜坡(黄土、泥岩二元层状结构)-地震触发(滑坡堆积体、坡体震裂损伤)-蠕变弱化(层间剪切带、裂缝和落水洞扩展)-降雨激发(滑带软化、泥化,水压力作用)-失稳滑动(滑面贯通)5个阶段;由于长期的蠕变和雨水的渗透冲蚀,坡体上的落水洞和地下暗河十分发育,且是控制本次滑坡边界的关键因素;滑坡后缘和前缘变形剧烈,中部变形相对稍弱,推断该滑坡为受地形及地下水作用控制明显的牵引-推移式复合滑坡。     

雅砻江甲西滑坡成因机制及其稳定性分析

甲西滑坡位于雅砻江中游某大型水电站水库库尾,是该区典型的一种滑坡类型。研究该滑坡的形成机制,对认识该区斜坡的变形破坏规律,评价库区斜坡的稳定性具有重要意义。该滑坡发育于由中薄层状砂岩与薄层状板岩互层组成的中陡倾角反向层状结构斜坡中,其变形破坏机制为倾倒弯曲-拉裂型。地质分析及简化毕肖普法稳定性计算结果表明,滑坡堆积体在自然状态下处于潜在不稳定状态,在特大暴雨和洪水作用下滑坡前缘有较大规模滑塌失稳的可能,但水库2 870 m蓄水位对滑坡的稳定性不起主导作用。     

青海尖扎盆地寺门村滑坡发育特征及成因分析

滑坡形成演化及复活一直是滑坡防灾减灾领域研究的热点问题。本文在对黄河上游尖扎盆地地质环境背景分析和滑坡体野外调查、遥感解译、实验测试的基础上,分析研究了盆地内寺门村滑坡的变形过程、滑带土和堆积体特征,还原了滑坡的演化过程,厘定了滑坡复活因素,提出了黄河上游滑坡堆积体开发利用对策建议,认为（1）该滑坡是2005年之前发生的老滑坡因河流侧蚀和2018年春季人工灌溉引发的复活性滑坡;（2）滑坡体综合治理应与土地整治相结合且应选择合适的灌溉方式。研究结果对于青藏高原东北缘黄河上游地区的滑坡防灾减灾及滑坡体开发利用具有重要意义。     

Engineering geomorphological interpretation of the Mitchell Creek Landslide,British Columbia,Canada

The recent assessment of the Mitchell Creek Landslide (MCL) in northern British Columbia is a good case history of engineering geomorphological analysis of a large landslide. It was completed using historic aerial photographs, with approximately 20-year time intervals dating back to the mid-twentieth century and field investigations completed between 2008 and 2014. The large bedrock slide initiated between 1956 and 1972 and continues to experience ongoing annual movements. Significant glacial downwasting and retreat has been observed in the photographic record, and it is hypothesized that alpine glaciation has contributed to development of the MCL. This paper documents four aspects of the engineering geomorphological assessment completed at the MCL: (i) topographic evolution, (ii) slope morphology, (iii) deformation features, and (iv) displacement behavior. Four distinct geomorphic zones have been defined at the MCL based on these analyses, controlled by different failure mechanisms. The extents of these zones have changed little over the documented history of the landslide, and rates of movement estimated from aerial photography have been consistent over the last 60 years. Retreat of the Mitchell Valley Glacier appears to have played an important role in landslide initiation, as the ice mass receded the kinematic freedom of the slope increased. This study of the initiation and development of the MCL demonstrates the capabilities of a multi-faceted approach to engineering geomorphology. The combination of historical aerial photographs with digital photogrammetric modeling and point cloud analysis techniques, and geomorphological mapping, allows for development of a robust understanding of landslide behavior.     

Mechanism of creep movement caused by landslide activity and underground erosion in crystalline schist, Shikoku Island, southwestern Japan

The mechanism of creep movement of the Zentoku landslide in crystalline schist has not been studied in detail because of the steepness of the slope, very slow movement, low population density and complex topographic and geologic characteristics. Sassa et al. (1980: Proc. INTERPRAEVENT 1, 85–106) and Sassa (1984: Proc. 4th International Symp. on Landslides, Toronto, vol. 2, pp. 179–184; 1985. Geotechnical classification of landslides, Proc. 4th International Conference and Field Workshop on Landslides, Tokyo, pp. 31–40; 1989: Landslide News, Japan Landslide Society, No. 3, pp. 21–24) monitored landslide movement and groundwater level at the Zentoku landslide on Shikoku Island, southwestern Japan, and suggested that the mechanism may be caused by underground erosion. To study the influence of underground erosion at this site, continual monitoring of suspended sediment and water discharge from a groundwater outlet (i.e. a spring) was implemented. The locations of groundwater flow paths were determined, as were the amounts of discharged sediment. Slope deformation was monitored by means of a borehole inclinometer. The conclusions were as follows: (1) the flow paths were found to be on or above the shear zones in which underground erosion has occurred; (2) in addition to being a result of precipitation and groundwater discharge, sediment discharge is affected by landslide activity; and (3) the mechanism of creep movement is an interrelated chain process that combines underground erosion caused by landslide activity with landslide activity caused by underground erosion. Thus, landslide activity increases erosion susceptibility and transportation of soils within the mass, and underground erosion causes instability of the landslide mass, in turn.

This mechanism can explain the observed phenomenon that the Zentoku landslide not only moves actively during heavy rain, but also continues to creep throughout the year.     

Rainfall patterns and related landslide incidence in the Porretta-Vergato region,Italy

An analysis of landslide occurrence in the low permeability terrain of Porretta-Vergato, Italy, related to prolonged rainfall patterns is presented. Data sets collected over nearly a century are statistically analysed. The pattern of the landslide hazard is considered and related to precipitation at the basin scale in order to enhance the understanding between the two parameters and assess their temporal changes, as well as interrelationships. Landslide incidence generally follows the periodic pattern of precipitation with a lag of approximately six months, which is believed to relate to the time necessary for the ground water to reach a critical level to initiate slope failure. There also appears to be a two-stage pattern of precipitation which induces most landslides: a preparatory period, where the landslide is destabilized and conditioned for slope failure, followed by a more intense period of rainfall that triggers or provokes the event. These initial findings point to the need for further studies to verify such unstable situations.     

湖北省香溪河流域白家堡滑坡稳定性分析与评价

三峡大坝建成蓄水后,将导致库岸部分古滑体复活、新滑体产生,香溪河流域白家堡滑坡就是其中之一。文章在对该滑坡的工程地质条件、深部位移及伸缩计监测资料的研究基础上,分析了滑坡变形机理,得出白家堡滑坡只有一个滑动面,其总体变形趋势为推移式,目前仍具有微小的变形。滑坡变形与降雨及库水有密切联系。结合试验资料,针对滑坡变形的实际情况,采用反演分析方法进行了滑移面抗剪强度参数的反演计算。利用反演结果,在三峡水库蓄水4种不同水位工况下进行稳定性计算。结果表明,滑坡的稳定性系数经历了大→小→大的过程。正常蓄水位时稳定性处于较低状态。滑坡体饱水处于蠕滑或失稳状态,需尽快进行治理。     

Development of Taprang landslide,West Nepal

This paper is about a large landslide located at Taprang, on the right bank of the Madi River in the west Nepal Himalaya. It attempts to reconstruct the evolution of the landslide from its initial state to the present conditions. Many large landslides involve multiple failure incidents in different times to attain their present size and shape. The Taprang landslide has also been active for more than 75 years and experienced many failure episodes. The slide lies in a very complex geological setting characterized by the presence of Main Central Thrust and some other folds as well as several joint sets and shear zones. It is developed on weathered graphitic schists, highly fractured and jointed quartzites, marbles, gneisses, and a few amphibolites. Landslide mapping revealed that the rocks are deformed and fractured. They have also undergone intense weathering. Laboratory analysis of rock and soil samples collected from the landslide and surrounding area shows that the weathered rocks, joint infillings, and shear zones are rich in clay minerals, especially smectite and montmorillonite having swelling properties. Besides, hydrologic, climatic, and anthropogenic factors operating simultaneously since a long time have also contributed significantly to the enlargement of the slide. The study indicates that the landslide has a high potential of future enlargement towards upper slopes.     

Mechanism for the rapid motion of the Qianjiangping landslide during reactivation by the first impoundment of the Three Gorges Dam reservoir, China

The first impoundment of the Three Gorges Dam reservoir in China started from a water surface elevation of 95 m on June 1, 2003 and reached 135 m on June 15, 2003. Shortly after the water level reached 135 m, many slopes began to deform and some landslides occurred. The Qianjiangping landslide is the largest one; it occurred on the early morning of July 14, 2003 and caused great loss of lives and property. Field investigation revealed that, although failure occurred after the reservoir reached 135 m, the stability of the slope was already reduced by preexisting sheared bedding planes. To study the mechanism of the rapid motion of this reactivated landslide, two soil samples were taken from a yellow clay layer and a black silt layer in the sliding zone, respectively, and a series of ring shear tests were conducted on the samples. One series of ring shear tests simulates the creep deformation behavior, while the other series simulates different shear rates. Conclusions drawn from analysis of the ring shear tests indicate that the mechanism of the rapid motion of the reactivated landslide was caused by the rate effect of the black silt layer during the motion phase after the creep failure. The yellow clay layer did not play any important role in the rapid motion in the 2003 event.