孟底沟坝前堆积体渗流特征及稳定性研究

发布时间：2018-07-09 13:58

本文选题：冰碛物 + 饱和-非饱和　；参考：《成都理工大学》2014年硕士论文

【摘要】：孟底沟坝前堆积体的稳定性对孟底沟水电站安全修建和运营有着至关作用和影响。通过现场详细的地质勘察,调查该工程区的工程地质特征,分析堆积体的空间展布、结构特征、地质成因,从整体上对孟底沟坝前堆积体作定性的判断。在整体认识的基础之上利用室内试验获得基本物理力学参数。由于坝前堆积体的工程特性,降雨和库水位变化时是对其稳定性影响最大的因素,本文运用饱和-非饱和土理论对孟底沟堆积体在不同降雨方案下和不同的库水位上升速率的条件下其渗流场特征进行全面的分析,得出孔隙水压力、体积含水率的变化规律,继而利用极限平衡法计算分析降雨、库水位变化对孟底沟堆积体稳定性的影响,这对工程建设是有指导性作用的。围绕堆积体的渗透特征和稳定性为中心,本文得到以下认识： 1.通过对堆积体所在地区地质历史、地形地貌特征、堆积体颗粒组成及结构特征等的调查分析,可以认为该堆积体应属我国西部地区末次冰期冰川运动遗留的冰碛堆积体。 2.通过室内大剪试验、大三轴试验、渗透试验获得了堆积体的天然和饱和抗剪强度指标、渗透系数,并提出了堆积体土样强度参数建议值。 3.降雨工况下,通过不同的降雨方案,同时考虑不同的渗透系数下堆积体的渗流特征,总体表现为：在总的降雨量保持相同的情况下,降雨强度较小,降雨历时较长的降雨入渗量更大,入渗深度更深,影响范围更大；同时由于在重力作用下,降雨呈现“坡脚汇集作用”,相比较而言,下部的入渗深度,入渗速率较上部大；从不同的渗透系数来比较,渗透系数越大其入渗能力越强,但非线性比例关系。 4.库水位上升的工况下,随着库水位按一定速率上升,堆积体前缘被水淹没,库水入渗,孔隙水压力上升,体积含水率增加趋于饱和直至库水上升至最大蓄水位2254m,地下水位达到稳定。在这一过程中地下水位的抬升相对于库水位的上升有明显的后滞,呈现库水位上升速率越快、渗透系数越小,滞后效应越明显的规律。 5.从稳定性变化来看,降雨入渗条件下决定堆积体稳定性的是最危险滑面的强度,三种降雨方案对孟底沟堆积体(k=k1取渗透性系数下限时)的稳定性系数在1.51左右几乎无影响,堆积体稳定性较好；当且仅当k=k2取渗透性系数上限时,降雨强度较小,降雨历时的越大的方案才会降低堆积体稳定性,而且表现出降雨历时越长,稳定性降低幅度越大的特点；对于库水位上升过程中,随着前缘逐渐淹没,稳定性系数逐渐降低,稳定性系数从1.151降低至1.06左右,直至地下水位稳定性,处于极限平衡状态。稳定性降低的幅度只与库水位上升的幅度有关,与库水位上升速率、渗透性系数无明显关系,而稳定性系数开始下降的时间和下降的速率与水位上升速率和渗透系数有关,总体表现为库水位上升速率越快渗透性系数越大,稳定性系数开始下降的时间越短,下降的速率也越快。
[Abstract]:The stability of the accumulation body in front of the mongdi gully dam has a vital role and influence on the safety construction and operation of the Mencian hydropower station. Through the detailed geological survey on the site, the engineering geological characteristics of the project area are investigated, the spatial distribution, structural features and geological causes of the accumulation body are analyzed, and the qualitative judgment of the accumulation body in front of the Mondi gully dam is made. Based on the overall understanding, the basic physical and mechanical parameters are obtained by indoor experiments. Due to the engineering characteristics of the pre dam accumulation, the variation of rainfall and reservoir water level is the most important factor for its stability. In this paper, the saturated unsaturated soil theory is used to determine the rising rate of the water level of the monddic gully accumulation under different rainfall schemes. Under the condition of the comprehensive analysis of the seepage field characteristics, the pore water pressure and the change law of the volume water content are obtained. Then the influence of the change of the reservoir water level on the stability of the Mondi gully accumulation body is calculated and analyzed by the limit equilibrium method. This has a guiding role for the construction of the project. It is centered around the permeability characteristics and stability of the accumulation body. This article gets the following understanding:
1. through the investigation and analysis of the geological history, topography and geomorphology, the composition of the particles and the structure characteristics of the accumulation body, it is believed that the accumulation body should be a moraine deposit left over by glacial movement in the last glacial period in the western part of China.
2. through the indoor large shear test, the large triaxial test and the permeability test, the natural and saturated shear strength indexes and the permeability coefficient are obtained, and the suggested values of the strength parameters of the soil sample are put forward.
Under 3. rainfall conditions, through different rainfall schemes and considering the seepage characteristics of the accumulations under different permeability coefficients, the overall performance is that under the same total rainfall, the rainfall intensity is smaller, the rainfall duration is longer, the depth of infiltration is deeper, and the influence range is greater; at the same time, the effect of gravity is greater. In comparison, the infiltration rate in the lower part is larger than that in the upper part, and the greater the permeability coefficient, the stronger the infiltration capacity, but the nonlinear proportional relation.
4. under the condition of rising water level, as the reservoir water level rises at a certain rate, the front edge of the accumulation body is flooded, the reservoir water is infiltrated, the pore water pressure rises, the volume water content increases to saturation until the reservoir water rises to the maximum water level 2254m, and the groundwater level reaches stability. The uplift of the groundwater level in this process is relative to the rise of the reservoir water level. The obvious hysteresis shows that the faster the water level rises, the smaller the permeability coefficient is, the more obvious the hysteresis effect is.
5. from the stability change, the stability of the accumulation body is the most dangerous sliding surface strength under the rainfall infiltration condition. The stability coefficient of the three rainfall schemes has almost no effect on the Mencius gully accumulation (k=k1 permeability coefficient lower limit), and the stability of the accumulation body is better. When and only when the permeability coefficient of the k=k2 is limited, the rainfall is limited. The smaller the intensity, the larger the rainfall duration will reduce the stability of the accumulation body, and show the longer the duration of the rainfall, the greater the stability reduction, the stability coefficient gradually decreases with the front edge drowning, and the stability coefficient decreases from 1.151 to about 1.06, until the groundwater level is stable. The amplitude of stability reduction is only related to the rise of reservoir water level, which has no obvious relation to the rising rate of reservoir water level and permeability coefficient, while the time and the rate of falling stability coefficient are related to the rising rate and permeability coefficient of the water level, and the overall performance is the faster permeability of the rise rate of the reservoir water level. The greater the coefficient, the shorter the time to start the descent of the stability coefficient and the faster the rate of descent.
【学位授予单位】：成都理工大学
【学位级别】：硕士
【学位授予年份】：2014
【分类号】：TV223.4

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