|Alternative Title||Experimental Study on the Formation Process of Rainfall-Induced Gravel Landslide post Earthquake|
|Place of Conferral||北京|
|Keyword||碎石土滑坡 模型试验 地震 动力响应 降雨|
地震作用改变了震区内斜坡岩土体的结构和物理力学性质，导致震后降雨诱发滑坡的数量和规模有明显的增大趋势。现有关于震后降雨型碎石土滑坡的研究，多采用理论分析与数值分析的方法，缺乏验证手段。因此，本文以汶川地震灾区震后降雨型碎石土滑坡为研究对象，基于资料查阅和现场调查，分析震后降雨型碎石土滑坡的地质特征、成因，建立了均质和含顺倾软弱夹层的碎石土斜坡的地质力学模型。通过开展一系列的振动台模型试验，分析震后降雨型碎石土滑坡的形成过程。本文得到的主要结论如下：（1）地下水对均质碎石土斜坡动力响应特征及变形破坏规律的影响无地下水的碎石土斜坡内部加速度峰值(PGA)放大系数呈高程放大，水平向PGA明显高于竖直向，随振动荷载强度的增加，坡体内部同一高程水平及竖直PGA增加；含地下水的碎石土斜坡内部PGA放大系数随高程的增加，呈先减小后增大的趋势；随着地下水位的增高，PGA放大系数的高程减弱区域增大，坡顶加速度动力响应效果减弱；随振动荷载强度的增加，坡体中下部同一高程水平或竖直向PGA减小。因此，地下水具有减震效果。 无地下水碎石土斜坡坡顶易发生破坏，随着地震荷载强度的增大，坡顶破坏程度加剧；含地下水碎石土斜坡易发生坡脚破坏，随着振动加速度及地下水位的增大，坡脚破坏的程度加剧。（2）含顺倾软弱夹层碎石土斜坡动力响应特征及变形破坏规律在地震荷载作用下，相比均质斜坡，含顺倾软弱夹层碎石土斜坡易发生滑动破坏。破坏模式为水平位移的动力响应呈高程放大，朝向临空面运动；竖直位移的动力响应呈高程增大，方向竖直向下；由于水平抛射及上下错动，软弱夹层或附近易产生裂缝，上覆土体发生滑动破坏。随软弱夹层倾角的减小或坡面角度的增加或地震加速度增大，坡体表面最大位移增大，坡体的稳定性下降。（3）坡体结构对坡顶加载压力的影响随着软弱夹层倾角的减小或坡面角度的增加或振动强度的增大，坡顶加载的影响区域增大，滑裂面位置在坡体内部更深的位置贯通，坡顶最大加载压力减小；与均质斜坡相比，顺倾软弱夹层的存在，使坡顶最大加载压力减小。（4）震后降雨型碎石土滑坡形成过程均质斜坡与含顺倾软弱夹层碎石土斜坡的形成过程既有相似性，也存在一定差异。相似性为：在地震荷载施加过程中，坡顶及坡面易形成横裂纹，坡体结构发生变化，下部振密，上部振松。坡体上部降雨入渗速度快，坡体下部降雨入渗速率慢，由于下部排水不畅，易产生超孔隙压力，细颗粒富集层积累水分，易成为潜在滑面，使抗剪强度下降，另外地表径流冲刷坡肩及坡面，发生表面侵蚀；差异性：在地震扰动作用下，软弱夹层易发生破碎，成为降雨入渗优先通道，又是潜在滑动面，较均质斜坡更易发生滑动破坏。 （5）震后降雨型滑坡孔隙水压力增长分为两种模式：a.缓慢上升型：前期无优先流通道产生，雨水经基质域入渗到传感器，逐渐积累，形成孔隙水压力；b.快速上升型：雨水沿优先流通道入渗，孔隙水压力快速上升。（6）采用水平条分法，利用Bishop对安全系数的定义，同时引入斜坡岩土体抗剪强度影响参量λi，计算推导了满足土条力和力矩平衡的，在振动荷载施加过程中以及振动荷载施加后降雨作用下斜坡稳定极限平衡计算公式。;
The structure and physico-mechanical properties of slope soils have been intensively changed by the effect of earthquake. The quantity and scale of rainfall-induced landslide post earthquake increases obviously. The existing researches on rainfall-induced gravel soil landslide post earthquake are mainly focused on theoretical analysis and numerical analysis, the means of verification is lack. Therefore, the rainfall-induced gravel soil landslide post 5.12 Wenchuan Earthquake is chosen as the objects. Based on the data access and field survey, the geologic feature and formation mechanism is analyzed. The geo-mechanical model slopes with uniform structure and dip weak interlayer are built up. Series of shaking table model tests and rainfall model tests are carried out to analyze the formation process of rainfall-induced gravel soil landslide post earthquake. The main results are as follows.(1)The effect of groundwater on the characteristics of dynamic response and the law of deformation and failure of uniform slopeThe amplification coefficient of peak acceleration of the uniform slope without groundwater increases as elevation increasing. The horizontal amplification coefficient of PGA is greater than vertical coefficient. As the increase of vibration load, the amplification coefficient of PGA of the same position increases.As elevation increasing, the amplification coefficient of PGA of the slope with groundwater decreases firstly and increases than. As the increases of water level, the region that PGA smaller than 1 enlarge and the dynamic response of acceleration on slope shoulder become weaker. As the increases of vibration load, the amplification coefficient of PGA of the same position in the lower-middle part of slope decreases. The groundwater have the effect of shock absorption.The existence of groundwater makes the slope easy to develop slope toe deformation. The slope without groundwater is more easily to develop slope shoulder deformation.(2)The characteristics of dynamic response and the law of deformation and failure of of slope with dip weak interlayerUnder the effect of earthquake, the slope with dip weak interlayer is easy to happen sliding. The failure mode is the dynamic response of horizontal displacement increases as elevation increasing, and the direction is toward the free face. The vertical displacement increases as elevation increaseing, the direction is downward. For the horizontal projectile and up-down movement, the position near weak interlayer is easy to produce fissure and the overlying soil layer occur sliding.As the decrease of interlayer angle or the increase of slope angle or the increase of acceleration, the displacement of slope surface increases and the stability decreases.(3)The effect of slope structure on the loading pressure on slope crest As the the decrease of interlayer angle or the increase of slope angle or the increases of acceleration, the effect region of loading pressure on slope crest enlarge , and the maximum pressure decreases. The position of slidng surface move backward and the shear opening move downward. The existing of dip weak interlayer decreases the maximum pressure of slope crest. (4)The formation process of rainfall-induced landslide post earthquake The formation process of slope with uniform structure and dip weak interlayer has both similarity and difference. The similarity is: Under the vibration load, the fracture formed on the crest and surface of slope, the upper part of slope becomes loose, the down part of slope becomes dense. The infiltrate speed of upper part of slope is fast and of middle-lower part is slowly. Because the down part is density, the drainage way is not clear. The excess pore pressure is forming. The concentration layer of fine particles accumulates water and become the potential sliding face. The shear stress decreases. The difference is: The weak layer is easily to be broken and form the preferential flow and potential sliding face, so it is easier to form landslide than uniform structure. (5) The mode of pore-water pressure increasing can be divided into two types:a. Increasing slowly: There is no preferential flow existing and the rainfall infiltrate into the slope through the matrix domain. The water accumulate little by little, pore-water pressure is formed. b. Increasing steeply: There is preferential flow existied and the rainfall infiltrate into the slope through the preferential flow firstly. The water accumulate quickly, pore-water pressure is formed. (6)Based on the horizontal slice method, the definition of Bishop safety factor and the influencing parameters λi which represents the shearing stress of slope soil, the limit equilibrium calculation formula of slope stability is deduced. This formula satisfis the equilibrium of forces and moment, and can calculate the stability under the effect of rainfall post earthquake or during the process of shaking.
|梁双庆. 震后降雨型碎石土滑坡形成过程试验研究[D]. 北京. 中国科学院大学,2016.|
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