干湿循环下非饱和土持水特性及边坡稳定研究

发布时间：2018-03-24 16:46

本文选题：干湿循环　切入点：非饱和土　出处：《南昌航空大学》2017年硕士论文

【摘要】：土质边坡常常处于干湿循环的环境中,在每个循环过程中土体的性质都在发生变化。目前对于干湿循环下土体性质变化的研究主要集中于土体抗剪强度的衰减,而长期处于干湿循环状态下的土质边坡,其土体持水特性变化的累计效应同样是不可忽略的,将直接影响到边坡的稳定性,从而成为导致边坡失稳的主要原因之一。本文以砂土、粉土和粘土为研究对象,重点研究不同类型非饱和土的持水特性受干湿循环作用的影响规律。在此基础上,采用数值计算的方法,首先研究干湿循环作用下,考虑非饱和土持水特性的变化与否对边坡渗流和稳定性的影响。其次,分析了干湿循环下不同土体饱和渗透系数、不同降雨条件和不同坡比条件对不同土质边坡的渗流场和稳定性的影响。最后,对比不同土质边坡在土工膜覆盖前后,其边坡渗流和稳定性的变化规律,探讨土工膜覆盖法加固边坡的可行性和有效性。本文的主要研究成果如下:(1)干湿循环作用导致非饱和土的持水特性发生变化,具体表现为随着干湿循环次数的增加,相同含水率条件下土体的基质吸力变小,即土体的持水能力出现不可逆的衰减。其中,粘土的持水能力受干湿循环的影响最小、粉土次之,砂土最大。随着干湿循环次数的增加,单次干湿循环对土体持水能力的衰减作用减弱。(2)干湿循环下,非饱和土持水特性的变化在一定程度上影响了边坡土体含水率的分布和边坡稳定性的变化。其中,雨强较大时,土体持水能力的衰减对粉土边坡的渗流和稳定性的影响较大;雨强较小时,土体持水能力的衰减对粘土边坡的渗流和稳定性的影响较大。(3)干湿循环下,土体饱和渗透系数大小和不同降雨条件对不同土质边坡的渗流和稳定性的影响程度主要取决于大气降雨强度和土体渗透系数之间的相对大小关系。坡度较缓的边坡稳定性较好。(4)土工膜覆盖法对粘土边坡的防护效果好于粉土边坡。对于粉土和粘土边坡,分别以膜覆盖边界水平向里约为3m和1m处开始,膜下土体基本不受大气降雨和蒸发的干扰。土工膜不同铺设方式的护坡效果对比:对于粉土边坡,土工膜直线形铺设的效果好于阶梯形,土工膜包边长度越短效果越好;而粘土边坡的规律正好相反。
[Abstract]:Soil slope is often in the environment of dry and wet circulation, and the properties of soil are changing during each cycle. At present, the research of soil property change under dry and wet circulation is mainly focused on the attenuation of soil shear strength. However, the accumulative effect of the change of soil water holding property is also not negligible when the soil slope is in dry and wet cycle for a long time, which will directly affect the stability of the slope. Therefore, it becomes one of the main causes of slope instability. In this paper, the effects of dry and wet cycles on the water holding capacity of different types of unsaturated soils are mainly studied with sand, silt and clay as the research objects. In this paper, the numerical method is used to study the influence of the variation of unsaturated soil water holding property on the slope seepage and stability under dry and wet cycles. Secondly, the saturated permeability coefficient of different soils under dry and wet circulation is analyzed. The influence of different rainfall conditions and slope ratio conditions on the seepage field and stability of different soil slopes. Finally, the variation of seepage and stability of different soil slopes before and after geomembrane covering is compared. This paper discusses the feasibility and effectiveness of geomembrane covering method for slope reinforcement. The main research results in this paper are as follows: 1) the dry and wet cycle results in the change of water holding capacity of unsaturated soil, which is manifested by the increase of dry and wet cycles. Under the condition of the same moisture content, the soil matrix suction becomes smaller, that is, the water holding capacity of the soil is irreversibly attenuated, among which, the water holding capacity of clay is the least affected by dry and wet cycle, and that of silt is the second. With the increase of dry and wet cycle times, the attenuation effect of single dry and wet cycle on the water holding capacity of soil is weakened. The variation of water holding capacity of unsaturated soil influences the distribution of soil moisture content and the stability of slope to some extent, and the attenuation of soil water holding capacity has a great influence on the seepage and stability of silt slope when the rainfall intensity is high. When the rain intensity is small, the attenuation of soil water holding capacity has a great influence on the seepage and stability of clay slope. The influence of soil saturation permeability coefficient and different rainfall conditions on the seepage and stability of different soil slopes depends mainly on the relative relationship between the atmospheric rainfall intensity and the soil permeability coefficient. The stability of slope is better than that of silt slope. For silt and clay slope, the effect of geomembrane covering method is better than that of silt slope. The horizontal direction of the film cover boundary is about 3m and 1m, respectively, and the soil under the film is not disturbed by atmospheric rain and evaporation. The slope protection effects of different laying methods of geomembrane are compared: for silt slope, The effect of geotextile linear laying is better than that of step, and the shorter the envelope length of geomembrane is, the better the effect is, but the law of clay slope is just the opposite.
【学位授予单位】：南昌航空大学
【学位级别】：硕士
【学位授予年份】：2017
【分类号】：TU43

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