Role of slope stability in cumulative impact assessment of hydropower development: North Cascades, Washington

Two environmental assessments considered the potential cumulative environmental impacts resulting from the development of eight proposed hydropower projects in the Nooksack River Basin and 11 proposed projects in the Skagit River Basin, North Cascades, Washington, respectively. While not identified as a target resource, slope stability and the alteration of sediment supply to creeks and river mainstems significantly affect other resources. The slope stability assessment emphasized the potential for cumulative impacts under disturbed conditions (e.g., road construction and timber harvesting) and a landslide-induced pipeline rupture scenario. In the case of smallscale slides, the sluicing action of ruptured pipeline water on the fresh landslide scarp was found to be capable of eroding significantly more material than the original landslide. For large-scale landslides, sluiced material was found to be a small increment of the original landslide. These results predicted that hypothetical accidental pipeline rupture by small-scale landslides may result in potential cumulative impacts for 12 of the 19 projects with pending license applications in both river basins.     

Techniques for slope stability analysis: Site specific studies from Idukki district,Kerala

The occurrences of slope failures are frequent in Idukki district of Kerala state particularly along the road cuttings and hill slopes causing disruption in traffic, loss of lives and property. This demands a critical evaluation of stability of slopes along the hill roads. This paper deals with stability analysis of a typical hard rock profile at Chuzhappu and a lateritic profile at Kumili along the road connecting Kottayam and Kumili. A large number of factors have been examined and studied; the orientation of discontinuities has been identified as one of the major inherent factors influencing slope instability along Chuzhappu hard rock profile. These have been analysed carefully using stereographic/equal area projection technique in order to determine the vulnerability to slope failure and to understand the type of rock slide that can occur in this profile. The buoyant force of water acting along the discontinuities after heavy rain storm further aids the down slope movement. As the laterite slope is mostly homogeneous, Bishops method and Swedish method were adopted for stability analysis of laterite slope at Kumili. The study also examines the efficacy and applicability of the different methods employed in soil mechanics to assess the stability of laterite slope.The results obtained by this method are compared by actual field conditions. The stability assessment indicates that two sectors at Chuzhappu and one sector at Kumili profile are at the geo-technical threshold of failure, when piezometric head rises during rainstorm. The study indicates that these methods are highly useful in determining the Factor of Safety in profiles with similar geological setting.     

东南沿海台风暴雨型单体斜坡灾害风险评价——以泰顺仕阳北坡为例

在东南沿海地区每年汛期由台风暴雨诱发的坡积层滑坡灾害事故众多,给当地人民生命财产安全造成巨大威胁。斜坡单体风险评价是地质灾害治理与防控的重点、难点。在野外调查、工程地质钻探及岩土体力学测试的基础上,以仕阳镇仕阳北坡为例,结合气象资料分析了不同降雨条件下斜坡的稳定性;采用蒙特卡洛方法计算了斜坡安全系数的统计特性;基于斜坡破坏概率研究了承灾体的易损性,并定量计算了不同降雨条件下建筑物及人员的风险值。结果表明：随着降雨强度的增加,滑坡发生概率随之增加,其风险值也逐渐增加,特大暴雨工况风险最大,其人员风险为94人/年,经济风险为1.41亿元/年。研究结果对东南沿海地区该类滑坡的防治工程有重要的参考意义,可为该类滑坡的防灾减灾决策提供建议。     

Slope stability analysis on a regional scale using GIS: a case study from Dhading,Nepal

A spatially distributed physically based slope stability model combined with a hydrological model is presented and applied to a 350-km² area located in Dhading district, Nepal. Land slide safety factor maps are generated for five cases, including three steady state conditions assuming either completely dry soils, half saturated soils, or fully saturated soils, and two quasi-dynamic conditions, i.e. soil wetness resulting from storm events with, respectively a 2 or 25-year return period. For the quasi-dynamic cases, two methods are used, one based on accumulation of groundwater flow from upstream areas, and the other on accumulation of soil water from direct infiltration. The methodology delineates areas most prone to shallow land sliding in function of readily available data as topography, land-use and soil types. For the study area only 29% of the soils are unconditionally stable, while 25% of the soils are found to be unstable under fully saturated conditions. The comparison between the methods based on contributing area or on infiltration for quasi-dynamic conditions show that the approach based on infiltration is more reliable for the study area. The proposed methodology for predicting landslide susceptibility on a regional scale, based on basic data in GIS form, may be useful for other remote regions where detailed information is not available.     

The role of sedimentation rate and permeability in the slope stability of the formerly glaciated Norwegian continental margin: the Storegga slide model

Despite the gently dipping slopes (ca 1°), large-scale submarine slope failures have occurred on the mid-Norwegian continental margin (Storegga, Sklinnadjupet, Traenadjupet), suggesting the presence of special conditions predisposing to failure in this formerly glaciated margin. With a volume estimated between 2,400 and 3,200 km³ and an affected area of approximately 95,000 km², the Storegga slide represents one of the largest and best-studied submarine slides of Holocene age known worldwide. Finite element modeling of slope failure indicates that a large (6.5 < Ms < 7.0) seismic triggering mechanism would not be sufficient to cause failure at more than 110 m below the seabed as observed for the slip planes at Storegga (northern sidewall). This implies that other factors (e.g., liquefaction, strain softening, gas charging, rapid burial) are needed to explain the occurrence of the Storegga slide with a deep surface of failure. In this paper, we discuss the importance of the compaction effect of rapidly accumulated sediments in the slide area. During compaction, sediment grains reorganize themselves, thereby, expelling pore water. Consequently, depending on sedimentation rate and permeability, excess pore pressures might result beneath less permeable sediments. Our modeling and cross-checking illustrate how excess pore pressure generation due to high sedimentation rate could explain the development of layers of weakness, and thus, how such a large slide might have been initiated in deep sediments. Using the highest sedimentation rate estimated in the area (36 and 27 m/kyr between 16.2 and 15 kyr BP), 1D modeling shows excess pore pressure values of around 200 kPa at a depth of 100 m below the seafloor 15 kyr BP and 60 kPa at a depth of 100 m at the time of the slide (8 kyr BP). Excess pore pressure apparently drastically reduced the resistance of the sediment (incomplete consolidation). In addition, 2D modeling shows that permeability anisotropies can significantly affect the lateral extent of excess pore pressure dissipation, affecting, that way, normally consolidated sediments far from the excess pore pressure initiation area.     

The role of slump scars in slope channel initiation: A case study from the Miocene Jatiluhur Formation in the Bogor Trough,West Java

This paper investigates slope channel initiation by seabed irregularities that were initially formed by slump scars in the lower to middle Jatiluhur Formation, part of the middle- to late Miocene successions in the Bogor Trough, West Java. This Miocene succession is up to 1000 m thick in the study area, and is interpreted as a prograding slope–shelf system that formed during a period of falling- and lowstand stages in relative sea level. The lower part of the formation is a siltstone-dominated siliciclastic succession, containing slump deposits, slump-scar-fill deposits, and minor channel-fill deposits, which formed in slope and shelf-margin environments. In contrast, the middle part, which gradationally overlies the lower part, is characterized by shallow-marine carbonates.The slump-scars-fill deposits have an overall lenticular geometry, and are 140–480 m wide and 0.4–1.6 m thick. Some have distinct erosional bases, which cut into the underlying siltstones, in association with medium- to coarse-grained sandstones with lateral-accretion surfaces and tractional structures common in channel-fill deposits. The incident link of slump-scar-fill deposits and channel-fill deposits in the prograding slope–shelf succession of the lower to middle Jatiluhur Formation suggests that some slump scars formed incipient seabed irregularities that may have played an important role in the development of slope channels. The present study provides one example of the various potential mechanisms that can result in channel formation in a slope setting.     

安徽芜(湖)-铜(陵)高速公路高边坡岩体结构特征与稳定性评价

根据芜-铜高速公路高边坡的实地调查与评估,论述了高边坡有不同的地层岩性和结构体所确定的边坡岩体结构类型,并且分析了各类边坡岩体结构的变形破坏与失稳模式。同时采用定性及定量分析方法确定岩石高边坡的稳定状况,由此对沿线高边坡的变形与失稳状况做出系统的分析与评价,预测和分析高边坡的变形与失稳破坏,对其提出针对性的防治工程意见与建议。     

Eolian processes,ground cover,and the archaeology of coastal dunes: A taphonomic case study from San Miguel Island,California, U.S.A.

Geomorphological evidence and historical wind records indicate that eolian processes have heavily influenced San Miguel Island environments for much of the Late Quaternary. The island is almost constantly bombarded by prevailing northwesterly winds, with peak velocities exceeding 75 km/h and wind gusts reaching over 100 km/h. These strong winds played an important role in the location, formation, and preservation of the island's more than 600 archaeological sites. Excavation and surface collection at a stratified Middle and Late Holocene archaeological site on the island's north coast suggest that wind related disturbances result in significant displacement of light fish bones, produce concentrations of shellfish and heavy mammal bones, and cause significant abrasion, etching, and polishing of bones, shells, and artifacts. These data illustrate that wind not only alters surface materials but can significantly disturb subsurface deposits to a depth of at least 20 cm. Working in concert with a variety of taphonomic processes, wind can play a fundamental role in the preservation of archaeological sites and careful scrutiny during excavation and laboratory analysis is required to delineate its effects. © 2002 Wiley Periodicals, Inc.     

The micromorphology of paraglacial and periglacial slope deposits: a case study from Morfa Bychan,West Wales,UK

Micromorphological analysis of the crudely stratified diamictons exposed in coastal sections at Morfa Bychan, west Wales, is presented and discussed. Three major units, Yellow Head, Blue Head and Brown Head, have been recognised, and their crudely stratified nature, plus clast orientations, indicate that they were all subject to mass movement down the flanks of the adjacent coastal hills. Earlier workers have suggested a periglacial environment for this mass movement, but recently it has been proposed that the Blue Head, at least, may have accumulated in a paraglacial environment through gravitational redistribution of recently deposited unstable till. It is shown here that the Yellow Head contains occasional dense silt-rich coatings on the upper surfaces of sand and gravel grains, although other cryogenic micromorphological phenomena were not observed. The Blue Head, however, contains no clear cryogenic micromorphological features, although there is abundant evidence for sediment shearing and grain rotation within the matrix. The Brown Head contains diffuse grain coatings and lenticular aggregates very similar to those observed elsewhere in periglacial solifluction deposits. Thus it is concluded that accumulation of the Blue Head was rapid, and took place in a paraglacial environment as a result of mudflow. The Yellow Head may represent periglacial solifluction immediately prior to glaciation, whereas the Brown Head accumulated above the Blue Head as a result of periglacial weathering of the adjacent exposed hill tops, and subsequent downslope solifluction of the weathering product. © 1998 John Wiley & Sons, Ltd.     

Application of rock mass classifications: a case study from Ituango hydroelectric diversion tunnel,Colombia

ABSTRACT

The local site experience is a valuable component for the success of rock mass classification systems as tunnel design methods. The Ituango hydroelectric project is a very important source of information in order to evaluate the usefulness of the main rock mass classification systems. The objective of this research is to improve understanding of some important features of excavated rock mass, such as discontinuities, block size, shear strength and joint alteration, by analyzing some hundreds of data obtained during excavation cycle.

The field study included a survey of exposures after drilling and blasting rounds. Rock mass classification and support measures for each type of terrain along 1400 m tunnel were performed. The rock mass classes could be better explained if shear strength, alteration or block size is calculated. The assessment of these data allows evaluating the block fall risk, improving support and liner. A local correlation between the RMR and Q system was also obtained.     

Geochemical diagnostics of metasedimentary dark enclaves: a case study from the Peninsular Ranges Batholith,southern California

Dark enclaves rich in amphibole and biotite are ubiquitous in granitoid rocks and typically represent fragments of mafic magmas, cumulates, restites, or country rocks. To develop criteria for identifying dark enclaves of non-magmatic origin, we investigated dark enclaves from a complete spectrum of light (carbonate- or feldspar-rich) to dark (amphibole-rich, biotite-rich, or composite) enclaves, reflecting progressive thermal and chemical equilibration with the host tonalite, the Domenigoni Valley pluton in the Peninsular Ranges Batholith, California. Metasedimentary dark enclaves have geochemical characteristics that overlap those of literature-compiled igneous dark enclaves. When compared with modelled igneous differentiation paths, metasedimentary enclaves can have anomalous CaO and K₂O contents for a given SiO₂, but other major-element systematics may not deviate noticeably from igneous differentiation trends. In addition, the fact that literature-compiled mafic enclaves trend towards high K₂O + CaO suggests that not all mafic enclaves are of igneous origin. In this work, we provide criteria for identifying enclaves of possible metasedimentary origin.     

The potential of point clouds for the analysis of rock kinematics in large slope instabilities: examples from the Swiss Alps: Brinzauls,Pizzo Cengalo and Spitze Stei

Landslides - Lidar measurements and UAV photogrammetry provide high-resolution point clouds well suited for the investigation of slope deformations. Today, however, the information contained in...     

岩石物性对油气成藏过程的控制作用——以塔里木盆地麦盖提斜坡为例

岩石物性能够影响和控制油气的运移和聚集过程.依据油藏物理模拟实验结果,我们认为塔里木盆地麦盖提斜坡古油气藏自新近纪上新世末期（大约2.0Ma）至今经历了一次重要的油气动态调整过程,这一过程将该区域在此之前形成的油气藏进行了重要改造,形成了现今油气藏.该区域的古油气藏动态调整与输导层和储层岩石的孔隙度φ密切相关,当岩石的孔隙度φ≤10%时,构成油气运移和聚集中的阻挡边界,油气沿阻挡边界运移,形成构造圈闭和岩性圈闭的复合型油气藏,在麦盖提斜坡群5井以北区域有发育和形成大型油气藏的有利地质条件.     

深层火山碎屑熔岩形成机理及其指相意义研究:以松辽盆地庆深气田为例

基于不同岩性、岩相条件从根本上决定了储集空间的发育程度与规模,所以找火山岩的储层集中表现为火山岩相、亚相的识别。文中以松辽盆地庆深气田为例,重点研究了深层火山碎屑熔岩形成机理及其在火山岩地质相和测井相识别中的意义。研究表明,火山碎屑熔岩类火山岩常见火山碎屑流、泡沫熔岩流、岩流自碎作用、近地表隐爆作用、再熔结(胶结)型5种成因类型,且不同成因火山碎屑熔岩具有明显不同的矿物岩石学特征和测井响应特征。根据其形成机理、矿物岩石学特征和FMI成像特征,认为上述5种成因类型的火山碎屑熔岩分别发育于爆发相热碎屑流亚相、介于爆发相和喷溢相之间的爆溢相、喷溢相、火山通道相隐爆角砾岩亚相、火山通道相火山颈亚相或近火山口相。该研究成果对于促进火山岩相、亚相的准确识别和优质储层的有效预测具有重要的指导意义。     

Continental growth at convergent margins facing large ocean basins: a case study from Mesozoic convergent-margin basins of Baja California, Mexico

Mesozoic rocks of the Baja California Peninsula form one of the most areally extensive, best-exposed, longest-lived (160 my), least-tectonized and least-metamorphosed convergent-margin basin complexes in the world. This convergent margin shows an evolutionary trend that may be typical of arc systems facing large ocean basins: a progression from highly extensional (phase 1) through mildly extensional (phase 2) to compressional (phase 3) strain regimes. This trend is largely due to the progressively decreasing age of lithosphere that is subducted, which causes a gradual decrease in slab dip angle (and concomitant increase in coupling between lower and upper plates), as well as progressive inboard migration of the arc axis.This paper emphasizes the usefulness of sedimentary and volcanic basin analysis for reconstructing the tectonic evolution of a convergent continental margin. Phase 1 consists of Late Triassic to Late Jurassic oceanic intra-arc to backarc basins that were isolated from continental sediment sources. New, progressively widening basins were created by arc rifting and sea floor spreading, and these were largely filled with progradational backarc arc-apron deposits that record the growth of adjacent volcanoes up to and above sea level. Inboard migration of the backarc spreading center ultimately results in renewed arc rifting, producing an influx of silicic pyroclastics to the backarc basin. Rifting succeeds in conversion of the active backarc basin into a remnant backarc basin, which is blanketed by epiclastic sands.Phase 1 oceanic arc–backarc terranes were amalgamated by Late Jurassic sinistral strike slip faults. They form the forearc substrate for phase 2, indicating inboard migration of the arc axis due to decrease in slab dip. Phase 2 consists of Early Cretaceous extensional fringing arc basins adjacent to a continent. Phase 2 forearc basins consist of grabens that stepped downward toward the trench, filled with coarse-grained slope apron deposits. Phase 2 intra-arc basins show a cycle of (1) arc extension, characterized by intermediate to silicic explosive and effusive volcanism, culminating in caldera-forming silicic ignimbrite eruptions, followed by (2) arc rifting, characterized by widespread dike swarms and extensive mafic lavas and hyaloclastites. This extensional-rifting cycle was followed by mid-Cretaceous backarc basin closure and thrusting of the fringing arc beneath the edge of the continent, caused by a decrease in slab dip as well as a possible increase in convergence rate.Phase 2 fringing arc terranes form the substrate for phase 3, which consists of a Late Cretaceous high-standing, compressional continental arc that migrated inboard with time. Strongly coupled subduction resulted in accretion of blueschist metamorphic rocks, with development of a broad residual forearc basin behind the growing accretionary wedge, and development of extensional forearc (trench–slope) basins atop the gravitationally collapsing accretionary wedge. Inboard of this, ongoing phase 3 strongly coupled subduction, together with oblique convergence, resulted in development of forearc strike-slip basins upon arc basement.The modern Earth is strongly biased toward long-lived arc–trench systems, which are compressional; therefore, evolutionary models for convergent margins must be constructed from well-preserved ancient examples like Baja California. This convergent margin is typical of many others, where the early to middle stages of convergence (phases 1 and 2) create nonsubductable arc–ophiolite terranes (and their basin fills) in the upper plate. These become accreted to the continental margin in the late stage of convergence (phase 3), resulting in significant continental growth.     

冻结滞水效应及其促滑机理 ——以甘肃黑方台地区为例

冻融期地质灾害的不断发生,愈来愈引起社会关注并被更多的学者所重视,甘肃黑方台地区冬春交接时期滑坡频发,是研究季节性冻融作用的首选之地.为了探索是否存在冻结滞水效应,揭示冻融作用诱发滑坡灾害机理,建立了气温、地温和地下水位动态等协同观测网.监测数据显示:黑方台地区存在季节性冻融现象,可划分为冻结期(秋冬)、完全冻结期(冬)、冻融期(春夏)、融化期(夏秋)的年季循环过程,也存在昼夜气温变化引起的循环冻融过程;斜坡中段冻结引起的地下水位上升了1.0m,证实了冻结滞水效应的存在.地下水模拟结果表明,冻结滞水引起斜坡坡脚水位壅高幅度超过3m,水平影响距离达到30m以上.冻结前坡体稳定系数为1.19;冻结后仅考虑冻结滞水效应引起的地下水位上升,稳定系数减小到1.09;反复冻融后,考虑黄土强度降低因素,坡体稳定系数降至0.97,说明冻结滞水效应和循环冻融的双重作用是滑坡在春季频发的根本原因.     

High-temperature rapid pyrometamorphism induced by a charcoal pit burning: The case of Ricetto,central Italy

Bulk chemistry and mineralogy of the peculiar rock of Ricetto (Carseolani Mts., Central Apennines, Italy) was studied to resolve its controversial origin: igneous dyke or anthropic product. This hybrid rock consists of a colorless, felsic component made up of glass plus quartz, and a brown, femic component made up of fans and spherulites of diopside, calcic plagioclase, wollastonite, and melilite. Textural relationships indicate very rapid cooling and immiscibility phenomena. The bulk chemistry of the rock is the same as that of the surrounding siliciclastic sandstone. The ¹⁴C analysis of a coal fragment from bottom of the body yields the conventional age of 227(±50) years. The Ricetto occurrence is an example of pyrometamorphism of a siliceous limestone induced by a charcoal pit burning. The small size of the heat source at Ricetto caused an intense but short-lived melting of the country rock. Prograde metamorphism caused a temperature increase up to 1,000–1,100 °C when melilite crystallization conditions were reached at appreciable P(CO₂) and high f(O₂). Melting occurred in a close system represented by the simplified equation: 3Cal+16.5Qtz+Ms+BtMel+Melt+2H₂O+3CO₂+0.5O₂. Diopside+calcic plagioclase+wollastonite formed by melilite breakdown during rapid cooling, through the reaction: 6Mel+6Qtz+0.5O₂3Di+2An+7Wo. Liquid immiscibility caused the separation between the felsic melt component and the femic melilite-bearing component. Immiscibility was characterized by different fractionation of alumina and alkalies between these two phases. Differences in bulk, glass, and mineral chemistry between the Ricetto and other melilite-bearing pyrometamorphic rocks can be attributed mainly to different protoliths.An erratum to this article can be found at     

Effects of fracture lineaments and in-situ rock stresses on groundwater flow in hard rocks: a case study from Sunnfjord, western Norway

Systematic field mapping of fracture lineaments observed on aerial photographs shows that almost all of these structures are positively correlated with zones of high macroscopic and mesoscopic fracture frequencies compared with the surroundings. The lineaments are subdivided into zones with different characteristics: (1) a central zone with fault rocks, high fracture frequency and connectivity but commonly with mineral sealed fractures, and (2) a damage zone divided into a proximal zone with a high fracture frequency of lineament parallel, non-mineralized and interconnected fractures, grading into a distal zone with lower fracture frequencies and which is transitional to the surrounding areas with general background fracturing. To examine the possible relations between lineament architecture and in-situ rock stress on groundwater flow, the geological fieldwork was followed up by in-situ stress measurements and test boreholes at selected sites. Geophysical well logging added valuable information about fracture distribution and fracture flow at depths. Based on the studies of in-situ stresses as well as the lineaments and associated fracture systems presented above, two working hypotheses for groundwater flow were formulated: (i) In areas with a general background fracturing and in the distal zone of lineaments, groundwater flow will mainly occur along fractures parallel with the largest in-situ rock stress, unless fractures are critically loaded or reactivated as shear fractures at angles around 30° to σ_H; (ii) In the influence area of lineaments, the largest potential for groundwater abstraction is in the proximal zone, where there is a high fracture frequency and connectivity with negligible fracture fillings. The testing of the two hypotheses does not give a clear and unequivocal answer in support of the two assumptions about groundwater flow in the study area. But most of the observed data are in agreement with the predictions from the models, and can be explained by the action of the present stress field on pre-existing fractures.     

地面伽马能谱测量在铀矿找矿中的应用研究--以黑龙江省嘉荫县磨石山地区为例

黑龙江省嘉荫县磨石山地区为火山岩分布区,为研究该地区的铀矿分布特征,采用地面伽马能谱测量方法对该地区进行测量,通过地面伽马能谱在该地区的应用,探讨了磨石山地区的铀异常分布特征,表明该方法在铀矿找矿中应用效果明显,为寻找铀矿提供了途径。