Preferential Flow And Stability Analysis Method For Fissure Clay Slopes

The existence and properties of fissures are the key factors that affect the engineering properties of fissure clay,and are also the inherent reasons that cause engineering problems of fissure clay slopes. Preferential flow is referring to the phenomena that water and solutes move quickly bypassing the soil matrix but from the preferential flow paths in the media including macropores. Preferential flow in the cracks of fissure clay is the exterior inducement that causes engineering problems of fissure clay slopes. So it is valued to carry out the research of preferential flow and stability analysis method for fissure clay slopes both for academic study and engineering application.The concept of preferential flow has been imported to the fissure clay slope seepage fields and stability analysis referring to the research achievement of soil preferential flow from the domestic and overseas scholars. The planar fissure clay preferential flow model has been established based on theoretical analysis and experiment. The influence of preferential flow in fissure clay has been showed by numerical simulation.The main research work and achievements of this paper are as the following:Firstly, the basic research of cracks in fissure clay has been carried out. An experimental device that can precisely control the local environmental humidity has been designed to explore for the rules of the formation,transformation,expanding of the cracks in fissure clay under climatic actions. The crack evaluation process reappears. The crack evaluation rules in the experiment have been summarized and the experimental phenomenon has been theoretically analyzed. The equation for crack emerging state and the conclusion that the direction of crack propagation turns by the stress boundary and the final crack development level reduces when the balance relative humidity rises have been gained.Secondly,the concept of the preferential flow has been introduced. The establishment thought,assumption conditions,basic mathematic-physics equations of preferential flow models are introduced, and the advantages and disadvantages of all the models have been compared. The contrast shows that there isn't a perfect model that has very strict physics meaning and has very simple mathematical expression form currently.Thirdly,laboratory and locale experiments have been designed and carried out aimed to preferential flow in fissure clay based on the introduce of theory. The laboratory experiment is the soil column drainage experiment. The great change of the soil seepage characteristics due to the existence of cracks has been showed by the contrast of the water movement rules of fissure clay and integrity clay under manual rainfall. The dyeing-tracing experiment and infiltration experiment have been carried out in locale. The measure data shows that the average infiltration capacity of different crack development level may be different by orders of magnitudes and it is mainly caused by the existence of cracks as preferential paths in fissure clay.Fourthly,the simple preferential flow model that is easily for engineering use for fissure clay slope has been established based on interrelated theory and experiments. The model that is based on the two-domain describes the water flow in crack-domain with kinematical method, and describes the water exchange between crack-domain and matrix-domain during the rainfall process as radiation from the crack-domain to the matrix-domain. The influence of preferential flow to the slope seepage fields has been studied with calculated examples.Finally,the results of the seepage have been used to the slope stability analysis and the influence of the preferential flow to the slope stability has been researched. The method of limiting-balance analysis and the unsaturated soil stress theory have been used. The analysis shows that the safety factors reduce greatly when the diminution of the fissure clay shearing capacity is considered and the controlling collapsing mode is parallel to the surface layer. The safety factors of cases when preferential flow is considered are less than cases when preferential flow is not considered, and the safety factors reduce constantly when the rainfall continues.