【作者】 刘雪梅；

【导师】 殷坤龙；

【作者基本信息】 中国地质大学 ， 地质工程， 2010， 博士

【摘要】 滑坡是斜坡破坏的一种典型模式,也是地貌演化过程的一种表现形式,滑坡的形成与地貌的演化过程密切相关。三峡库区具有典型的河谷型地貌特征,且层状地貌十分明显,库区内地貌的演化和区域构造背景和新构造运动密切相关,层状河谷地貌为库区滑坡的形成提供了基本条件。区内滑坡受地貌、地质构造等共同影响,具有区域集中、活跃期一致的特点。万州区是三峡库区地质灾害防治的重点区域,集中分布了多个特大型近水平地层滑坡,很难通过力学平衡解释近水平地层滑坡的成因。普遍认为,岩层内原生的软弱夹层是滑坡滑带形成的介质,暴雨引起后缘拉裂缝充水,形成的静水压力是推动滑坡启滑的关键。在此过程中,河谷地貌的演化对近水平地层滑坡的作用不容忽视。万州区近水平地层滑坡具有相似的地貌、地质组合特征,根据高程分布,自上而下依次为,危岩陡崖、古滑坡和前缘松散堆积体,这种组合体现了河谷不同演化阶段的地质特征。为了揭示万州区近水平地层滑坡的启滑机制,分析地貌演化和滑坡成因间的关系。首先,论文在总结前人研究成果的基础上,将区域地质背景和新构造活动特点相结合,分析了三峡库区典型河段河谷地貌的演化过程,将系统演化的基本模式用于地貌和滑坡形成过程分析。然后,总结了三峡库区万州区滑坡的特点,并系统地分析了滑坡区的地质环境和古气候环境,研究了万州区苎溪河古河道的变迁过程,进而探讨了万州区古滑坡与区内地质环境演化过程之间的关系。最后,以万州区山湾滑坡后缘拉裂槽钻孔资料为基础,将地质判别和数值模拟分析相结合,重建万州区河谷地貌的演化过程,探讨区内近水平地层滑坡的成因机制。论文取得了以下阶段性、创新性研究成果。(1)根据三峡库区构造和地貌格局,以奉节为界,将库区地貌划分为东西两个单元。东段为三峡峡谷,西段为四川盆地东部的低山丘陵区,河谷地貌以宽谷为主。两大地貌单元分别受四川台坳和八面山台褶带两个大地构造单元影响。在新构造运动期,地壳阶段性隆升,形成了以高山峡谷兼多级夷平面和阶地为特点的河谷地貌,剖面图上层状地貌明显。(2)库区内构造线通常控制着水系、山体的延伸。库首至巴东段地貌主要受黄陵背斜和秭归向斜影响,大的水系从向斜周边流经,如香溪河。沿向斜核部发育的水系,多呈枝状分布。巴东至奉节段受齐耀山断裂带和一系列紧密型褶皱影响,长江河谷与构造线多近于平行或斜交。奉节至重庆段属川东褶带,由一系列NE向的紧密背斜和宽缓向斜组成。(3)新构造运动以来,阶地相对河床的抬升速度有所增加,库区内地壳隆升在空间上分布不均衡,奉节和巫山一带处于相对快速隆升区,这种相对快速隆升趋势自更新世即存在,全新世更加明显,使得阶地在奉节地区存在明显的拐点。同一地区阶地发展规律基本相似,均表现为时代新的阶地抬升速度快,老阶地抬升速度慢。现今地壳主压应力方向NEl2°～60°,地壳主压应力近似水平。根据万州和巴东地区河谷地貌,认为前期坡体以下切运动为主,在侵蚀基准面下降后,岸坡表现为陡崖的不断崩塌后退或滑坡,后期则表现为水平的改造,总体上讲,河谷坡体演化过程均以水平下降为主。(4)三峡库区河谷地貌演化过程受内部营力子系统、外动力子系统及地质体子系统的综合作用。前两者属于相对较活跃的子系统,容易发生物质和能量的变化。地貌演化通常表现为系统的缓变过程,而滑坡则是系统的突变过程。将地貌和滑坡看作开放系统,采用信息熵理论对区域斜坡危险性进行预测,选择地形地貌、地表岩组、松散堆积层厚度、不良地质现象、库岸再造、土地利用类型和治理加固工程等指标对万州区斜坡危险性进行了预测。(5)万州城区斜坡具有明显的“上崩下滑”特点。斜坡后缘普遍存在陡崖,以崩塌为主,陡崖逐渐后退；斜坡中部为近水平古滑坡体,古滑体后缘普遍发育拉裂槽,裂槽底部连接深部滑面,滑面由岩层原生软弱夹层形成。斜坡前缘发育崩滑堆积体,堆积体地表和底面均呈现为多级台阶状,是区内主要的变形体。目前,城区滑坡的危害主要来自前缘的崩滑堆积体变形。(6)受河流的侧蚀和下切作用,苎溪河岸坡临空,在暴雨时,发生大面积的崩滑,迫使河道持续变化,总体呈由南向北变迁的趋势。河流阶地是万州区滑坡形成的基础,七大古滑坡除草街子和太白岩滑坡滑面平均高程较低(滑面高程为191m和186m),对应于万州河谷Ⅲ级阶地高程,其他的古滑坡滑面高程均分布在215-240m高程范围内,对应着万州地区Ⅳ级阶地高程,即Q22～Q23(第四纪中更新世中、晚期)的产物。岩层间原生软弱夹层以蒙脱石等亲水矿物为主,遇水易软化形成滑带。古滑坡形成时期均处于全球气候暖期,降雨在岸坡后缘裂缝内形成静水压力,具备发生平推式滑坡的条件。万州红层的互层结构岩体,在水位变动带易崩解,随着河流持续下切,古滑坡前缘形成崩塌堆积体。在此过程中也存在河流的沉积,形成了与阶地高程对应的混杂松散堆积体基座平台。苎溪河南岸前缘堆积体滑坡均与二级阶地形成时间相当或在二级阶地形成后发生。局部边缘地带在T1时期发生滑动,如草街子滑坡东侧,和平广场滑坡前缘松散体。松散堆积体表现为多级滑动的模式。(7)山湾滑坡拉裂槽钻孔资料显示,沉积物白下而上分布为：完整基岩、碎裂岩、碎石土(块石)和粉质粘土(淤泥),其中碎石土和粉质粘土来自崩塌堆积物和山湾堰塘沉积。崩塌堆积物具有明显的崩塌旋回特征,松散堆积物测年显示,形成时代自下而上依次变新,最底层层堆积物对应于万州区Ⅲ级阶地的形成时期。山湾滑坡典型剖面的拉裂槽内,松散堆积物共有10次崩塌旋回,在崩塌旋回6以前的平均崩塌堆积速率为44.43m2/ka,崩塌旋回7-10的平均崩塌堆积速率为36.92m2/ka。根据典型剖面推测,单次崩塌旋回堆积物厚度平均值为3.2m,滑坡后缘陡崖的后退速率约0.31～0.37m/ka。根据阶地的高程和测年结果,将滑坡区河谷看作五次的分期下切,通过数值模拟分析了河谷下切和山湾古滑坡的形成的关系。由于万州区原生沉积的软弱夹层中含蒙脱石和伊利石等亲水粘土矿物,在河谷下切初期的卸荷回弹作用下,沿软弱夹层首先发生塑性变形。河谷下切至T3阶地时,夹层临空,在上覆坡体的自重压力作用下向临空方向发生塑性挤压,沿软弱夹层形成剪张破裂区。之后,后缘坡面拉裂区和内部软弱夹层拉裂区共同扩展,致使后缘拉裂缝贯通。在暴雨期,后缘拉裂缝充水,形成较大的静水压力,推动山湾滑坡启动。随之,形成后缘拉裂槽,水头迅速降低,滑体也很快制动。在后期,由于降雨无法再形成高的水头,古滑坡处于稳定状态。目前,河谷斜坡的破坏区主要分布在河谷前缘的崩滑堆积体分布区。更多还原

【Abstract】 Landslide is not only a typical model of slope failure, but also an expression form of landform evolution, so the generating process of landslide is related to landform evolution closely. The Three Gorges Reservoir Region has the typical characteristics of valley-type topography, and the layered terrain is very apparent. The geomorphic evolution inthe reservoir is closely related to the regional tectonic setting and the new tectonic movement, the landform also provides a basic condition to the formation of landslides in reservoir area.Wanzhou City is a key area in prevention and control of geological disasters in the Three Gorges Reservoir Region, a number of large gentle-dipped landslides are concentrated in this district, but it is difficult to explain the causes of formation of approximately horizontal strata landslide through the mechanical balance theory. It’s generally considered that the weak intercalated layer native in rock is the medium with the formation of landslide zone, when there is a heavy rain, hydrostatic pressure caused by water-filled in pull cracks in the back edge is a key point to make landslide happen by pushing the approximately horizontal strata. In this process, the role of the river valley landform evolution to the approximately horizontal strata of landslides can not be ignored. Gentle-dipped landslides in Wanzhou District have similar combined features of landforms and geology, the elevation distributions of from top to bottom are unstable rock cliffs, ancient landslides, and loose accumulation body, which reflects the evolution of geological features of ancient landslides in different stages.In order to reveal the slip mechanism of gentle-dipped landslides in Wanzhou District and to analyse the relationship between landform evolution and landslide formation causes, Firstly, based on the summy of research combined the regional geological setting and the new features of tectonic activity, the papar analyses the evolution process of a typical river landscape in the Three Gorges Reservoir Region and analyse the evolution of geomorphology and landslide by using the basic model of the system evolution. Secondly, the characteristics of landslide in Wanzhou District is summarized, geological environment and ancient climate environment in the landslide area systematically analysed, as well as the changes in the process of the ancient riverway of Zhuxi River in Wanzhou District are studied in the paper, then explore the relationship between the ancient landslide in Wanzhou District and the local geological environment evolution. Lastly, based on the borehole data of back edge of rupture of Shanwan landslide in Wanzhou District, the author combines geology differentiation and numerical simulation analysis, studies the river valley landform evolution and explore the formation mechanism of the gentle-dipped landslides in this area. This paper has got the following stage, innovative research results.(1) According to tectonic and landscape patterns in the Three Gorges Reservoir Region, with the boundary of Fengjie, physiognomy of the reservoir divided into two units, east part and west part, the east unit is the Three Gorges canyon, the west unit with main area of wide vale is the low hill area of the east part of Sichuan basin. Two topography units are respectively impacted by those two tectonic units, Sichuan col and Bamian Mountain fold belt. Affected by the new tectonic movement of crustal uplift stage, topographic features of the reservoir which with characteristics of high mountains and canyons, as well as multi-level terrace and planation surface, have significant layered profile landforms.(2) Tectonic lines in the reservoir are usually in control of the water system and the extension of the mountain. The landform between the top of the reservoir and Badong is mainly affected by Huangling anticline and Zigui syncline, and large rivers flow from the peripheral of the syncline, such as Xiangxi river. It also has some water systems developing along the syncline core, distributing like branches. Affected by Qiyao fault zone and a series of compact folds, the Yangtze River almost paralleled to or oblique crossing the tectonic line. Fengjie to Chongqing belongs to Chuandong fold belt, which is composed of a series of compact anticlines and broad syncline in NE direction.(3) Since the neotectonics, the elevating speed of the Terrace is higher than the riverbed. The crustal uplift in the reservoir appears spatially unbalanced. There is a trend of rapid uplift between Fengjie and Wushan. The trend exists since the Pleistocene, more distinct in the Holocene, resulting in some inflexions to the terrace in the Fengjie region. However, the development of the terrace is basically similar in the same region. It appears that new terrace uplifts fast, while old terrace uplifts slow. Presently, the direction of the principal compressive stress of the crustal is NE12°～60°, which is parallel to the water level.(4) The geomorphological map of valley in Wanzhou and Badong shows that, in the prophase, the slope is mainly doing the undercutting movement. When the base level of erosion go down, it appears that the cliff on the bank slope may collapse backwards constantly or slide downhill. In the later stage it appears to be horizontal transformation. Generally speaking, the evolution of the valley slope is mainly the horizontal decline.The evolution process of the Three Gorges valley geomorphology is affected by the comprehensive effect of the inner agent subsystem, external force subsystem and geologic body subsystem, the former two subsystem are relatively more active, they are easily to change in material and energy. The geomorphology evolution is often a slow process, while the landslide is a mutation process.Considering geomorphology and landslide as an open system, using the information entropy theory in the risk prediction for the regional slope, choosing landform and geomorphology, surface rock group, the thickness of loose accumulation layer, bad geological phenomenon, reservoir bank rebuilding, land-use type and management reinforcement projects to predict the risk of slopes in Wanzhou.(5) Wanzhou City has a significant slope "on the collapse down" feature. After the edge of cliffs slope common to collapse mainly cliffs recede; in the middle of the slope is nearly a level ancient landslide body, the ancient landslide margin after the general development of fracturing tank, split tank connected at the bottom of the deep sliding surface, sliding surface by the rock the formation of a native soft interlayer. Leading-edge developments slump-slope accumulation body, accumulation of body surface and bottom are presented as a multi-stage step-like deformation of the main body of the region. Urban landslide hazards mainly come from the leading edge of the slump-deformation accumulation.(6) Zhuxi River Slope overhead, during rainstorms by the river Side erosion and the downward cutting action, a large area of Slump, forcing river constantly changing, the overall change was from south to north trend.River terraces are formed by the landslide in Wanzhou District, besides the average height of Grass Street slip is low (slip surface elevation of 191m), the other seven ancient landslide slip surface elevation are distributed in 215-240m elevation range corresponds to the Wanzhou district gradeⅣterrace elevation is Q22～Q32 (Middle Pleistocene in the Quaternary and late) product. Soft interlayer between the native rock work as montmorillonite and other minerals mainly hydrophilic, with water forming easy to soften the sliding zone. The ancient landslide was formed from a global warming period, rainfall in the bank slope form the back edge hydrostatic pressure within the fractures with flat push sliding.The ancient landslide was formed earlier than the edge accumulation body, and in the river continued to the next cutting process, the leading edge of the ancient landslide accumulation of body transformation by rivers. Wanzhou red layer structure of alternating layers of rock, in the water level change with easy to collapse, in the collapse of river sediment accumulation at the same time there is formed with the terrace height corresponds to the base platform for hybrid loose accumulation body.Zhuxi River south edge accumulation landslides are related to the formation of the time gap two grade terraces occered or occurred after the formation of terraces. Local fringe slide occurred in the T1 period, such as sub-landslide east of Grass Street, Peace Square, loose body landslide front. Loose bodies piled up with multi-level sliding mode.(7) Mountain Bay Landslide fracturing tank borehole data show that from button to up distribution of sediments are:a complete rock,broken rock, gravel, earth (rock), and silty clay (mud). And silty clay deposits from the collapse and mountains bay weir deposition, landslides deposits have obvious features of collapse cycle, and loose deposits dating show that the formation of a new era of bottom-up changes followed, corresponds to the city of gradeⅢandⅣterraces formative years.In Mountain Bay landslide typical fracturing tank, the average failure rate of accumulation is roughly 44.43m2/ka when the Collapse cycle is below six cycles,and the average failure rate of accumulation 36.92m2/ka when the average collapsed cycles is 7-10,the average thickness of 3.2m in a single collapse cycle deposits, landslides trailing edge escarpment retreat rate is between 0.31 and 0.37m/ka.更多还原