第一章 地质环境
Chapter 1 Geologic Environment
三峡库区地层岩性较为齐全多样。前震旦系变质岩和岩浆岩分布于东端莲沱—庙河间及其两岸(黄陵背斜核部),坝址即位于其上;震旦系至三叠系浅海、滨海相碳酸盐夹碎屑岩,主要分布于庙河—香溪(黄陵背斜西翼),以及官渡口—大宁河和乌江等库段及其两岸;三叠系上统至侏罗系陆相碎屑岩,广泛分布于香溪—官渡口(秭归盆地)和奉节以西(川渝盆地,即原“四川盆地”东部)库段及其两岸。大坝以东的下游两岸(江汉盆地东部)尚有白垩—第三系陆相碎屑岩;第四系松散堆积物,零星分布。
The strata lithology of Three Gorges Reservoir Area is of great variety. Metamorphic rock and magmatic rock of pre-Sinian system are distributed between rivers Liantuo and Miaohe in the east and its two-side banks (the core of Huangling anticline where Three Gorges Dam lays on). The carbonate rocks with intercalated clastic rocks of neritic and littoral facies form Sisian system to Triassic system are mainly distributed from Miaohe to Xiangxi (the west flank of Huangling anticline), between the Guandukou and the Daning River, as well as Wujiang River reservoir section and their side banks. The clastic rocks of continental facies of upper Triassic system and Jurassic system are widespread from Xiangxi to Guandukou (Zigui Basin), west reservoir section of Fengjie County (the east of Sichuan Basin) and its side banks. The clastic rocks of continental facies of Cretaceous system and Tertiary system are distributed at side banks of lower reaches of the east of Three Gorges Dam (the east of Jianghan Basin). The Quaternary systems of loose deposits are sporadic distribution.
三峡库区地质构造复杂。东端为北北东向穹隆状黄陵背斜,其西,为鄂西渝东北北东(西部)到北东东(东部)向弧形梳状褶皱带;相邻的北部为大巴山与荆山—大洪山北西西(西部)至北西(东部)向弧形线状褶皱带;相邻的南部为八面山北东(西部)至东西(东部)向弧形箱状褶皱带。它们经历多次构造运动形成,但主要定型于侏罗纪末的燕山运动。新生代以来,三峡库区地壳运动主要表现为间歇性隆起。
Geological structure of Three Gorges Reservoir Area is quite complicated. Its eastern part is vault Huangling anticline with a strike NNE. Its western part structurally lays in arc-comb fold belt with an axial strike from NNE in the west to NEE in the east within the range of west Hubei Province and northeast Chongqing City. Its adjacent northern part is arc-line fold belt of Dabashan Mountain, Jingshan Mountain and Dadongshan Mountain with an axial strike from NWW in the west to NW in the east. Its southern part is arc-box fold belt of Bamianshan Mountain with an axial strike from NE in the west to EW in the east. They have undergone multiple tectogenesis and fixed in the Yanshan movement at the end of Jurassic period. The crustal movement in Three Gorges Reservoir Area has been intermittent uprising movement since Cenozoic era.
三峡库区地形,以奉节为界,以西以渝东低山丘陵,河谷较为开阔,仅局部狭窄;以东为鄂渝中低山地,河谷深切,间有宽谷。库区地形特征与岩性相吻合,山地走向与构造基本一致。
Bounded on Fengjie County, the topography of the west of Three Gorges Reservoir Area mainly takes the shape of low hills in eastern Chongqing City, and valleys are fairly wide and a few is narrow. The topography of the east is low-mean mountainous region in Hubei Province and Chongqing City, and the valleys are deep dissection and a few are wide. The topography feature of Three Gorges Reservoir Area is coincident with strata lithology, and the strike of the mountains is in coincidence with the structure as well.
三峡库区气候为亚热带季风气候,温和湿润,降雨充沛。多年平均气温16.7~18.7℃,多年平均降雨量987~1326mm,5~9月多暴雨。
The climate of Three Gorges Reservoir Area belongs to subtropical monsoon climate that is mild and humid with abundant rainfall. Its perennial average temperature is 16.7℃ to 18.7℃ and its perennial average rainfall is 987mm to 1326mm. There are lots of storms from May to September.
长江干流宜昌站多年平均年径流量约4510亿m3,多年平均流量14300m3/s,最大洪峰流量71100m3/s,最枯流量2770m3/s,每年5~10月为汛期。
Perennial average runoff of Yichang City oberservation station lying in Yangtze River mainstream is about 4510×108m3 and perennial average flow is 14300m3/m. The flow of flood peak is 71100m3/s and the least flow is 2770m3/s. Flood season is from May to October every year.
三峡库区岸坡类型,按组成的岩性可分为四类:Ⅰ、松散松软土质岸坡;Ⅱ、块状结晶岩岸坡;Ⅲ、层状碳酸岩岸坡;Ⅳ、层状碎屑岩岸坡。其中:Ⅳ类岸坡占绝大多数,崩塌、滑坡最发育;Ⅲ类岸坡居第二位,崩塌、滑坡发育程度次之;Ⅰ类岸坡分布零星,滑坡较发育;Ⅱ类岸坡最少,在其表部风化壳中,可发育小型滑坡。Ⅲ、Ⅳ两类层状岸坡,按岩层产状与岸坡坡面产状关系,可分为顺向、斜向、横向、反向等岸坡。层状岸坡,用其他指标还可进行细分。在不考虑其他因素情况下,其崩塌、滑坡发育程度由强到弱的顺序是:顺向坡—斜向坡—横(反)向坡,但岸坡的稳定性和崩滑变形破坏机制在很大程度上受控于组成岸坡的岩土性质及其软弱面(层、带)有有无、多少和产出状态以及坡体的形态。
The bank slope types of Three Gorges Reservoir Area can be classified into four categories according to lithological composition. The first is loose and soft earth slope, the second is massive crystalline rock slope, the third is bedded carbonate rock slope and the forth is bedded clastic rock slope. The forth is major slope and the easiest to collapse and landslide, and third slope is the next. The first slope is limited and easier to landslide. The second slope has the least distribution and only its weathering surface crust can slightly landslide. The third and forth bedded slopes can be classified into four types as the following: consequent slope, insequent slope, transversal slope and reversal slope according to the relation of slopes orientation and strata occurrence. They can be also classified detailedly using other indication. Generally, the order of the development of caving and sliding from strong to weak are consequent, insequent, transversal (reversal). However, slope stability and deformation and destruction mechanisms of collapse and slide are mainly controlled by the nature of rock and earth of bank slope, the existence, number and occurrence of its weak face (layer or zone), as well as slope pattern.
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郭希哲,黄学斌,郭满长等,三峡工程库区崩滑地质灾害防治图册[M],北京:中国水利水电出版社,2008