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1.
第四纪冰期大型山岳冰川运动遗留下的大型冰水堆积体是我国西南高山峡谷地区一类重要的第四系堆积物.本世纪以来,随着该地区大型基础工程的陆续上马,这种大型冰水堆积体的存在常常成为工程建设必须面临的工程地质问题,这些冰水堆积体因其形成演化过程的特殊性,使得其在结构、物质组成、力学特性、水理特性等诸多方面与一般松散堆积体存在显著差别,因而研究其结构特征、形成演化过程以及带来的工程地质问题具有重要意义.以澜沧江某电站坝前冰水堆积体为例,在调查分析其结构特征的基础上,对冰水堆积体的形成演化过程进行分析和研究,并对冰水堆积体的工程特性,以及带来的工程地质问题进行了探讨,认为该冰水堆积体的工程特性明显好于其他第四系松散堆积体,电站蓄水后整体失稳的可能性较小,但其前缘仍存在局部失稳的可能. 相似文献
2.
泥石流堆积体的抗剪强度指标包括内擦角φ和凝聚力C。φ、C值是泥石流防治工程设计中的重要参数,影响着防治工程建筑物的投资费用和运行安全性。目前国内外对泥石流堆积体抗剪强度试验的文献尚不多见。因此在泥石流防治工程设计中,多沿引水工等有关资料或凭经验采用。为了进一步探讨泥石流堆积物的抗剪强度指标,1985年夏,在泥石流暴发频率较高的云南东川蒋家沟,进行了泥石流堆积体的抗剪强度试验。 相似文献
3.
澜沧江乌弄龙电站坝前崩塌堆积体发育特征及稳定性评价 总被引：1，自引：0，他引：1
云南澜沧江乌弄龙电站地处滇西北山区,坝前500 m处有一近480×104m3的大型堆积体。该堆积体长1 200 m,宽100~200 m,厚8~10 m,具有上部收敛、中部约束、下部发散的分区特征,各区段内堆积物在块度组成、剖面结构、植被发育、坡度变化等方面都显示出一定的对应特征。这样一个大型堆积体置于坝前显然对未来建坝蓄水存在安全隐患。因此,在分析其现有变形动态的基础上,结合大剪试验和对堆积体休止角的统计资料,选择合理的力学参数进行稳定性计算。结果表明,该堆积体在天然状况下处于临界稳定状态,这与其目前的实际情况一致,但在蓄水后堆积体会产生失稳破坏。最后,针对堆积体自身的结构和分区特征,提出相应的防护措施和建议。 相似文献
4.
利用理学DMAX-3C衍射仪(CuKa,Ni滤光)、偏光显微镜、扫描电镜(SEM)、岩石直接剪切蠕变试验系统等对武隆鸡尾山滑坡滑带软岩进行矿物成分、岩性鉴定并分析构造和组分,自然风干和饱水后两种状况的显微结构观察,并对其流变特性进行试验研究。其结果为:软弱带方解石含量占68%、有机质13%、滑石9%、蒙脱石5%、石英4%、白云石1%,滑动面的镜面物质没有变化。显微结构测试结果表明:自然风干后在扫描电镜下,样品中出现大量的线型擦痕、微孔隙和微裂隙,粘土矿物呈定向排列。充分饱水后试样出现新的微裂纹,并有扩张现象,孔隙明显增大,也较好的吻合了该滑坡滑动的一些基本事实。对直剪流变试验与快剪试验获得的抗剪强度参数相比较发现,前者的长期抗剪强度有显著降低,摩擦系数降低31.53%,凝聚力降低37.61%,且凝聚力对剪切流变特性的影响高于内摩擦系数。这些试验结果与野外对滑坡的调查结果相吻合,促进了对滑坡的机理研究;滑带软岩的微观结构及流变力学性质是该滑坡发生蠕滑效应的重要因素。 相似文献
5.
通过压力板仪、temple仪和直剪仪对非饱和粉土经过脱湿之后和不同含水量状态分别进行抗剪强度试验研究。试验结果表明:如果采用净应力来描述,非饱和土的有效粘聚力随着含水量的增大而减小,或随着基质吸力的增大而增大,但有效内摩擦角基本保持不变。当饱和度相同时,经过脱湿之后的土体有效粘聚力较大,反映出滞回效应。如果采用有效应力来描述,抗剪强度曲线则归一化为一条临界状态线,而与含水量大小和水力路径无关,从而证明了采用有效应力的合理性与有效性。在修正剑桥模型基础上,将饱和度和基质吸力作为内变量,提出屈服强度的硬化函数,建立渗流与变形耦合模型,从而可以考虑前期降雨历史对非饱和土边坡稳定性的影响。 相似文献
6.
7.
孔隙率对黄土抗剪强度具有非常重要的影响,然而,孔隙率对黄土抗剪强度影响效果的认识并不充分。本文以陕西省延安黄土为研究对象,开展不同孔隙率的黄土直剪试验研究,探讨了孔隙率对粘聚力与内摩擦角的定量变化关系;并以此为基础,构建了基于孔隙率的延安黄土抗剪强度模型,并对其进行了验证。研究结果表明:(1)延安黄土粘聚力与孔隙率间呈幂函数变化关系;(2)延安不同孔隙率黄土内摩擦角取值呈现出两个区间,当孔隙率n≥0.4时,其内摩擦角在25±2.5°的范围内变动,而当孔隙率n<0.4时,其内摩擦角在29.5±2°的范围内变动;(3)通过分析得到了基于孔隙率的延安黄土抗剪强度模型,且该模型得到的黄土抗剪强度理论值与实测值间的误差较小,相对误差均在7%以内,具有较高的精确度。研究成果不仅能为延安黄土抗剪强度研究等提供技术支持,而且还能为该地区的工程建设等方面提供理论参考。 相似文献
8.
重塑黄土抗剪强度对黄土重大工程的长期稳定与安全有着极其重要的影响,然而,由于传统测试方法的限制,对于结合水与抗剪强度之间关系的认识并不充分。本文基于无损、可靠、精确与便捷的核磁共振技术,针对不同含水率的重塑黄土开展了结合水发育特征与重塑黄土抗剪强度的试验研究。利用结合水与自由水的冰点不同,寻找二者的核磁共振信号界限—T_2截止值,然后获取不同含水量直剪试样的核磁共振驰豫曲线,最后结合快剪试验分析结合水含量与土体抗剪强度的关系。试验结果表明:(1)重塑黄土内结合水含量随含水量的上升而增多,且增长趋势逐渐变缓,结合水所占比例也在不断地下降。(2)当土体内含水量增大时,并不会单独发育某一赋存状态的水,而是在某个含水率区间内主要发育某一种赋存状态的水。(3)重塑黄土中结合水的增加会导致粘聚力的降低,对内摩擦角没有明显影响。重塑黄土试样内结合水主要是通过削弱土体的粘聚力从而降低黄土土体抗剪强度,且土体内结合水含量与粘聚力c值及抗剪强度大小呈线性负相关。本文研究成果可为非饱和黄土边坡与高填方工程的稳定性计算等方面提供技术支持与理论参考。 相似文献
9.
水蚀作用下土壤抗蚀能力的表征 总被引：18，自引：2，他引：18
研究区为黄土高原南部淳化县泥河沟流域 ,在未经翻耕的自然或人工 (耕地 )坡面上 ,选择 5 6个 1m2样地 ,(土壤为黄土 ,体积含水率 7.1%～ 2 0 .1%,干容重 1.0 1g/cm3～ 1.2 9g/cm3) ,采用南京土工仪器厂出产的WI- 3型便携式直剪仪 ,对表层 0～ 5cm土层进行现场取样剪切 ,3次重复剪切的结果表明 ,表层土壤抗剪强度与土壤含水率及容重均密切相关。抗剪强度起初随含水率增加而缓缓增大 ,在含水率 12 %～ 14%时达最大 ,然后较迅速减弱。容重的影响表现为 :随容重增大 ,土壤抗剪强度呈直线趋势较快增大。通过室内降雨侵蚀实验 (坡面面积为0 .3m× 1.0m ,雨强分别为 1.39、1.49、1.88和 2 .6 6mm/min) ,经对收集的溅蚀物及冲刷物称重分析发现 ,无论击溅侵蚀还是径流击溅共同作用 ,在土壤干容重不变 ( 1.2 g/cm3)情况下 ,试验土壤含水率达 16 %时 ,其抗蚀能力最强。考虑到容重的影响 ,把抗剪强度作为抗蚀力指标还是较为合理的。对于表层为松散状态的坡面 ,将分别采自农耕地、荒地、草地、灌木地表层的原状土块 ( 2 5cm× 6cm× 2 .5cm)用水饱和后 ,置于长 10 0cm、宽 6 .2cm、高 6 .0cm的冲刷槽中 ,在坡度 15° ,流量 5L/min条件下进行等时冲刷。用冲刷前后同一土样重量之差除以流量 ,即可求出冲刷模数值。经对 相似文献
10.
《山地学报》2016,(6)
为研究雨林乔木类树种的根系存在对红粘土土质边坡的加固效果,并从根系形态、几何特征方面研究其加固机理,选取海南热带雨林地区常见的四类直根系乔木树种进行现场大型剪切试验和根系实地统计,获取不同深度下根-土复合体的剪应力与位移关系曲线,并取相应的原状土进行室内直剪试验,将现场剪切试验条件下测得的根-土复合体抗剪强度与室内素土抗剪强度进行比对,计算出不同根-土复合体土体抗剪强度增长率,最终得出在现场原位条件下,四类树种根系中小叶榄仁根-土复合体抗剪强度的增长率最大,其次是重阳木根系和凤凰木根系,非洲楝根系最差;对于四类树种来说都存在一个最优根土面积比,使得根系能最大限度地发挥自身提高土体抗剪强度的作用。 相似文献
11.
The final stage of deglaciation of Hudson Bay was a major Holocene catastrophic event marked by the drainage of Lake Agassiz/Ojibway at ~ 8.47 ka cal BP and the rapid collapse of the Laurentide Ice Sheet. Previous work undertaken in the Nastapoka River area (eastern Hudson Bay) demonstrated that during the relative sea level highstand that shortly followed the drainage of the lake, the western margin of the Québec–Labrador ice sector rapidly retreated eastward to reach a stillstand position in a coastal hill range. In this study, an analysis of Landsat 7TM images has allowed a mapping of large-scale glacial landforms (outwash deposits, eskers, flutings, and De Geer and Rogen moraines) between Kuujjuaraapik (SE Hudson Bay) and Puvirnituq (NE Hudson Bay). The key results from this mapping are: i) ice-contact outwash deposits mapped along the entire arc-shaped coastline of the eastern Hudson Bay outline a major ice stillstand phase in the coastal hills that extended at least from Kuujjuaraapik to Inukjuak. The presence of these hills allowed a stabilisation of the ice margin that led to the accumulation of thick and extensive ice-contact submarine fans. ii) The position of these deposits on the down ice side (west) of large sets of flutings indicates an important phase of sediment delivery by a rapid ice flow phase toward a marine-based ice margin. iii) A second system of outwash deposits observed farther inland indicates a subsequent phase of stabilisation of the ice margin during its retreat toward central Québec–Labrador. 相似文献
12.
MA&#;GORZATA PISARSKA-JAMRO&#;Y 《Geografiska Annaler: Series A, Physical Geography》2008,90(3):237-249
The study area in Mysliborz Lakeland (Western Pomerania), NW Poland, is located in the glaciomarginal zone of the Pomeranian Phase (Weichselian glaciation). Three subenvironments of deposits are exposed in the six analysed pits: glacial ice-contact subenvironment, transitional subenvironment and glaciofluvial subenvironment. The glacial ice-contact subenvironment is dominated by coarse-grained, massive and thick beds derived from debris flows and also horizontally laminated sand and gravel deposited by sheet flows. The transitional subenvironment represents deposits between end moraine and proximal outwash plain (sandur). The transitional subenvironment is dominated by coarse-grained diamicton derived from debris flows, horizontally laminated beds deposited by sheet flows, and additionally cross-stratified sediments from channel flows and massive sand from hyper-concentrated flows. The glaciofluvial subenvironment corresponds with the distal part of the glaciomarginal zone. The processes of sediment deposition in the glaciofluvial subenvironment are derived from shallow sheet flows and channelized flows. Architectural element analysis highlights the change in lithofacies associations from glacial ice-contact, through transitional to glaciofluvial subenvironments. This sedimentological zonation of the glaciomarginal zone may have been developed in other glaciomarginal belts and remains to be recognized. 相似文献
13.
R. Rieu † P.A. Allen‡ † J.L. Etienne§ † A. Cozzi¶ † U. Wiechert&#; 《Basin Research》2006,18(4):471-496
The Ayn Formation of the Neoproterozoic Mirbat Group comprises <400 m of little‐deformed, glacially influenced basin margin deposits. These deposits are preserved in several palaeovalleys eroded in crystalline basement and overlain by a discontinuous cap carbonate. The Ayn Formation and the cap carbonate, which are superbly exposed along a 20 km SW–NE‐striking escarpment in south Oman, provide important insights into the processes operating on a basin margin during a Neoproterozoic glaciation and its demise. The Ayn Formation comprises units of glacimarine rain‐out diamictite and sediment gravity flow deposits, alternated with units of fluvial and deltaic sandstones and conglomerates, which may have formed by proglacial outwash. The stratigraphic evolution of the Ayn Formation indicates a highly active hydrological cycle during a phase of overall (glacio‐eustatic?) low stand when glaciers advanced into and receded upon bedrock valleys. The transgressive cap carbonate was deposited primarily in shallow marine or shallow lacustrine environments over palaeohighs during the deglaciation, and was partly reworked into deeper parts of the basin through sediment gravity flow processes. Locally, the cap carbonate transgresses over crystalline basement containing a network of fissures filled with carbonate originating from the cap. The δ13C isotopic composition of the cap carbonate varies systematically between ?3.5 and +5.8‰ Pee Dee Belemnite standard, in common with other older Cryogenian examples. 相似文献
14.
Juraj Janocko 《Geografiska Annaler: Series A, Physical Geography》1997,79(1-2):57-66
Southeast-northwest trending longitudinal ridges are conspicuous morphological features at Lågjæaren, southwest Norway. They have been interpreted as either marginal push-moraines, deposited by a southwesterly flowing glacier, or drumlins, which originated during advance of a northwesterly flowing glacier. The paper presents results of morphological, sedimentological and glaciotectonic analyses of one of these ridges at Obrestad. It is suggested that the ridge has been formed by drumlinization of outwash deposits by a glacier advancing towards the northwest and subsequently deformed by a southwesterly flowing glacier. 相似文献
15.
天山南麓台兰河口丘状堆积物成因及时代的新见解 总被引：2，自引：0，他引：2
研究表明台兰河口的丘状堆积体属古泥石流成因，物质组成显示泥石流形成于中低山带的峡谷段，泥石流可能由谷坡堆积物（主要为钙质胶结的冰碛）滑塌阻塞河床发展而成。其形成时代晚于末次冰期，应在全新世中期或更晚一些。 相似文献
16.
François Charlet Marc De Batist Emmanuel Chapron Sébastien Bertrand Mario Pino Roberto Urrutia 《Journal of Paleolimnology》2008,39(2):163-177
Prior to the collection of a series of sediment cores, a high- and very-high-resolution reflection seismic survey was carried
out on Lago Puyehue, Lake District, South-Central Chile. The data reveal a complex bathymetry and basin structure, with three
sub-basins separated by bathymetric ridges, bedrock islands and interconnected channels. The sedimentary infill reaches a
thickness of >200 m. It can be sub-divided into five seismic-stratigraphic units, which are interpreted as: moraine, ice-contact
or outwash deposits (Unit I), glacio-lacustrine sediments rapidly deposited in a proglacial or subglacial lake at the onset
of deglaciation (Unit II), lacustrine fan deposits fed by sediment-laden meltwater streams in a proglacial lake (Unit III),
distal deposits of fluvially derived sediment in an open, post-glacial lake (Unit IV) and authigenic lacustrine sediments,
predominantly of biogenic origin, that accumulated in an open, post-glacial lake (Unit V). This facies succession is very
similar to that observed in other glacial lakes, and minor differences are attributed to an overall higher depositional energy
and higher terrigenous input caused by the strong seismic and volcanic activity in the region combined with heavy precipitation.
A long sediment core (PU-II core) penetrates part of Unit V and its base is dated as 17,915 cal. yr. BP. Extrapolation of
average sedimentation rates yields an age of ca. 24,750 cal. yr. BP for the base of Unit V, and of ca. 28,000 cal. yr. BP
for the base of Unit IV or for the onset of open-water conditions. This is in contrast with previous glacial-history reconstructions
based on terrestrial records, which date the complete deglaciation of the basin as ca. 14,600 cal. yr. BP. This discrepancy
cannot be easily explained and highlights the need for more lacustrine records from this region.
This is the second in a series of eight papers published in this special issue dedicated to the 17,900 year multi-proxy lacustrine record of
Lago Puyehue, Chilean Lake District. The papers in this special issue were collected by M. De Batist, N. Fagel, M.-F. Loutre
and E. Chapron. 相似文献
17.
Christian Schlüchter Pierre Gander Thomas V. Lowell & George H. Denton 《Geografiska Annaler: Series A, Physical Geography》1999,81(2):347-358
Folded outwash occurs in four distinct clusters in an arcuate arrangement just west of the terminal Llanquihue moraines deposited by the Lago Llanquihue piedmont ice lobe at the last glacial maximum. These clusters are physically connected along the eastern side to the Llanquihue terminal moraines, and along the western side to the Llanquihue outwash plain. Each cluster consists of three to eleven elongated ridges. The maximum height of individual ridges varies from cluster to cluster beween 18 and 28 m; the maximum length of individual ridges is between 93 and 1074 m. The average orientation of the ridges ranges over a 60° sector relative to former ice-flow direction. The folded out-wash sediments are cut by two distinct internal fault systems with only a faint surface expression below the Holocene top soil.
The folded outwash ridges are interpreted as a push moraine system produced by the same mechanical forces that act in a critically tapered wedge. The folded sediment is a sandy gravel with an angle of friction on the order of φ = 40°. Interpretations of structural data and of mechanical comparisons point to a basal thrust plane in a sand unit with φ between 24° and 30° and with a pore water pressure index of l = 0.7.
It is very unlikely that the observed and analyzed features wereformed under permafrost conditions. 相似文献
The folded outwash ridges are interpreted as a push moraine system produced by the same mechanical forces that act in a critically tapered wedge. The folded sediment is a sandy gravel with an angle of friction on the order of φ = 40°. Interpretations of structural data and of mechanical comparisons point to a basal thrust plane in a sand unit with φ between 24° and 30° and with a pore water pressure index of l = 0.7.
It is very unlikely that the observed and analyzed features wereformed under permafrost conditions. 相似文献
18.
Sebastian H. Mernild M.Sc. & Ph.D. Bent Hasholt 《Geografisk tidskrift / udgivet af Bestyrelsen for Det Kongelige danske geografiske selskab》2013,113(2):13-25
A classification of watercourses proposed by Hasholt 1999 has been tested in Denmark using data from detailed field investigations from 42 watercourses and their surrounding area. Three types of landscapes are included: the moraine landscape from the Weichselian glaciation, the moraine landscape from the Saalian glaciation and the outwash plains. The performance of the classification in separating types of watercourses is discussed and modifications are suggested. 相似文献
19.
This paper provides data on the landforms, soils, and sediments within a unique northern Michigan landscape known as the Grayling Fingers, and evaluates these data to develop various scenarios for the geomorphic development of this region. Composed of several large, flat-topped ridges that trend N–S, the physiography of the “Fingers” resembles a hand. Previously interpreted as “remnant moraines”, the Grayling Fingers are actually a Pleistocene constructional landscape that was later deeply incised by glacial meltwater. The sediments that comprise the Fingers form a generally planar assemblage, with thick (>100 m), sandy glacial outwash forming the lowest unit. Above the outwash are several meters of till that is remarkably similar in texture to the outwash below; thus, the region is best described as an incised ground moraine. Finally, a thin silty “cap” is preserved on the flattest, most stable uplands. This sediment package and the physiography of the Fingers are suggestive of geomorphic processes not previously envisioned for Michigan.Although precise dates are lacking, we nonetheless present possible sequences of geomorphic/sedimentologic processes for the Fingers. This area was probably a topographic high prior to the advance of marine isotope stage 2 (Woodfordian) ice. Much of the glacial outwash in the Fingers is probably associated with a stagnant, early Woodfordian ice margin, implying that this interlobate area remained ice-free and ice-marginal for long periods during stage 2. Woodfordian ice eventually covered the region and deposited 5–10 m of sandy basal till over the proglacial outwash plain. Small stream valleys on the outwash surface were palimpsested onto the till surface as the ice retreated, as kettle chains and as dry, upland valleys. The larger of these valleys were so deeply incised by meltwater that they formed the large, through-flowing Finger valleys. The silt cap that occupies stable uplands was probably imported into the region, while still glaciated. The Fingers region, a col on the ice surface, could have acted as a collection basin for silts brought in as loess or in superglacial meltwater. This sediment was let down as the ice melted and preserved only on certain geomorphically stable and fluvially isolated locations. This study demonstrates that the impact of Woodfordian ice in this region was mostly erosional, and suggests that Mississippi Valley loess may have indirectly impacted this region. 相似文献