| 题名 | 元谋干热河谷主要崩塌类型的发生机制 |
| 作者 | 陈安强 |
| 学位类别 | 博士 |
| 答辩日期 | 2012-05-18 |
| 授予单位 | 中国科学院研究生院 |
| 授予地点 | 北京 |
| 导师 | 刘刚才 |
| 关键词 | 元谋干热河谷 崩塌类型 发生机制 稳定性分析 |
| 其他题名 | Development Mechanism of the Main Landslip Styles in the Yuanmou Dry-Hot Valley |
| 学位专业 | 自然地理学 |
| 中文摘要 | 元谋干热河谷区沟蚀崩塌充分发育，冲沟的发育为崩塌的发生提供了崩塌潜势，而崩塌的发生又促进了冲沟的发育，沟蚀崩塌成为该区侵蚀产沙的主要来源。本研究通过对元谋干热河谷土体崩塌类型的全面调查和运用模拟试验等手段，对影响崩塌的因素和崩塌形成的过程机制进行了详细研究，主要研究结果如下：（1）元谋干热河谷土体崩塌类型分为沟头掏蚀形成的坠落崩塌、沟壁侧蚀形成的滑落崩塌和土柱的倾倒崩塌。元谋干热河谷崩塌的发生与冲沟的发育、特殊的地质构造、土体特性、气候特征和水流特征密不可分。冲沟发育为崩塌的发生创造了崩塌潜势；元谋组地层特殊的地质构造，为沟头和沟壁近似直立发育创造了条件，并形成了不同的地形地貌特征；燥红土、变性土和砂土层（来源于河湖相沉积的砂层）由上往下成层分布，以及三种土层机械组成、力学特性、入渗特性及抗侵蚀能力等特性的差异，引起降雨和径流的选择性侵蚀，最后在元谋干热河谷气候干、热，干湿季明显的气候背景下，各种因素相互影响，相互作用造成了干热河谷内不同类型崩塌的大量形成。（2）沟头表层径流对下层砂土层的冲掏引起了坠落崩塌的发生。每次冲刷试验过后，沟头淘洞形态具有相似变化的特征。流量越大，形成的跌水流所占总流量的比重就越大；壁面流的掏蚀作用要大于跌水流。壁面流占总流量比重随雷诺数和弗汝德数的增加呈指数函数降低，跌水流占总流量比重随雷诺数和弗汝德数的增加分别呈对数函数和幂函数增加。淘洞的发育使上层粘性土呈悬空状态，当掏蚀达到临界深度时，悬挂土体发生了崩塌。悬挂土体存在拉张裂缝时，裂缝的发育加速了坠落崩塌的发生。根据崩塌时崩塌体的形态特征，建立的两层崩塌土体的稳定性分析模型，运用该模型能够较好的预测沟头的坠落崩塌。（3）沟道水流对下层砂土层的侧蚀是引起沟壁崩塌的主要因素，试验中不同流量的水流切应力（1.71～8.55 Pa）远大于砂土起动的临界切应力（0.13 Pa）；水流冲刷引起的沟壁砂土层的侧向后退距离公式为ΔBs = 20.131Ct Δt (t - tc) e -1.3τc/ γs +0.0047；砂土层的侧向后退是引起沟壁悬挂土体的崩塌，并建立了沟壁发生剪切破坏和拉伸破坏时的稳定性分析模型。在80 cm和120 cm构造土体的冲刷试验中，砂土层的侧向冲刷距离分别为0.312 m和0.35 m时，悬挂土体发生旋转破坏（Fsb和剪切破坏（Fa=0.974﹤1），悬挂土体上部拉张裂缝的发育加速了土体的失稳而发生崩塌。 = 0.767﹤1）（4）变性土胀缩过程中，土体在垂直方向和水平方向变形是各向异性的，其胀缩过程特征曲线可以用三直线模型较好的拟合；变性土的膨胀收缩引起裂缝的发育，裂缝的连通度、宽度和面积随着循环次数的增加而增加。黏聚力和内摩擦角随着裂缝发育的增加而降低，裂缝发育对黏聚力的影响程度明显大于内摩擦角。裂缝发育及土体强度的降低造成了变性土的不断剥落。土墙或土柱下层变性土的剥落是引起倾倒崩塌的主要因素。根据土墙和土柱倾倒崩塌时的发生机制，建立了4种稳定性评价模型。对4类倾倒崩塌的稳定性分析，表明下层变性土不断剥落形成的崩塌潜势比潜在崩塌体底部结构面贯通对土体稳定性的影响要大，而且后缘裂缝的充水高度的增加也降低了土体的稳定性。 |
| 英文摘要 | Gully erosion and landslip are outstanding and main sources of erosion and sediment yield in Yuanmou Dry-Hot Valley area. The gullying developed the potential of landslip occurrencefield survey and the simulation experiment in Yuanmou Dry-Hot Valley. Main results were summarized as follows:, while the landslip occurrence in turn accelerated the gully development. In this study, the influence factors and formation mechanism of landslip were studied by the (1) The landslip could be divided into three types in Yuanmou Dry-Hot Valley: the falling collapse of gully head, the sliding landslip of gully cliff and the topplinglandslip of soil column. The landslip occurrence was closely related to gully development, special geological structure, soil body properties, climate features and flow characteristics. The gully development formed the potential of landslip occurrence. The special geological structure of Yuanmou Formation formed the settings for the approximation vertical development of gully head and gully cliff, and developed the different topography and geomorphology. The dry red soil, vertisol and sand soil layer (from fluvio-lacustrine deposits of sand layer) were stratified from top to bottom. There were significant differences in soil particle size distribution, mechanical properties, infiltration characteristics and anti-scourability between the three layers. These differences caused the preferential and selective erosion of rainfall and runoff. The mutual influence and interaction of setting factors resulted in the formation of different types of landslip under the climate background with the dry-hot and distinct wet and dry season in Yuanmou Dry-Hot Valley. (2) The surface runoff on gully head scoured the lower sand soil layer and caused the occurrence of falling landslip of the upper hanged soil body. The change of scour hole shape was similar after every scour test. The greater the flow was, the greater the proportion of off-wall flow was. On-wall flow played a more important role in the development of scour hole than off-wall flow did. The ratio of on-wall flow to total flow decreased in an exponential function with the increase of Reynolds number and Froude number, while the ratio of off-wall flow to total flow increased in a logarithmic function and a power function with the increase of Reynolds number and Froude number. The development of scour hole made the upper clay layer hanging. The hanged soil body collapsed when the scour hole reached a critical depth. When the tension cracks appeared in the upper hanged soil body, these cracks development accelerated the occurrence of falling collapse. The stability analysis model of two layered soil body for collapse was established according to morphological characteristics of the layered soil body. This model could well predict the falling landslip of the gully head. (3) The gully cliff landslip was mainly attributed to the lateral flow erosion at lower sand layer on gully cliff. The shear stresses of different flows were within 1.71～8.55 Pa, and they were much higher than the critical shear stress(0.13 Pa) of sand flow starting up. The flow scouring led to the lateral wall recession in sand layer. The formula of lateral wall recession distance was ΔBs = 20.131Ct Δt (t - tc) e -1.3τc/ γs +0.0047. The lateral wall recession finally resulted in the collapse of hanged soil body of gully cliff. The stability predition models of gully cliff for rotating failure and shearing failure were established. The overhanging soil body would make the occurences of rotating landslip (Fb = 0.767﹤1) and shearing landslip (Fa=0.974﹤1) when the lateral wall recession distance approached 0.312m and 0.35m for 80 cm and 120cm height of modelled gully cliff, respectively. The cracks development of hanged soil body accelerated the soil body instability and the occurrence of landslip. (4) Vertisol body deformations in vertical and horizontal directions were anisotropy in the expansion and contraction process. The characteristic curve of the expansion and contraction could better fit the three kinds of linear model. The expansion and contraction of vertisol caused the crack development. The connectivity, width and area of the cracks gradually increased with increase of thetest numbers. The cohesion and internal friction angle gradually decreased with the increase of crack development. The impact of crack development on the cohesion was greater than that on the internal friction angle. The crack development and reduction of soil body strength induced the constantly exfoliation of vertisol. The main factor of the toppling was the exfoliation of vertisol in the lower of soil column and soil wall. The four kinds of stability prediction models of toppling were developed according to occurrence mechanism of toppling of soil column and soil wall in Yuanmou Dry-Hot Valley. The results from the stability analysis of the four types of the toppling, showed that the impact of the formation of landslip potential cuased by constantly exfoliation of lower vertisol on the stability of soil body was greater than that of structure surface transfixion of potential landslip body bottom, and the increase of water-filled height of the trailing edge crack reduced the stability of soil body. |
| 语种 | 中文 |
| 公开日期 | 2013-01-15 |
| 内容类型 | 学位论文 |
| 源URL | [http://192.168.143.20:8080/handle/131551/4812]  |
| 专题 | 成都山地灾害与环境研究所_山地灾害与地表过程重点实验室 |
| 推荐引用方式 GB/T 7714 | 陈安强. 元谋干热河谷主要崩塌类型的发生机制[D]. 北京. 中国科学院研究生院. 2012. |
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