Soft Clay Micro-quantitative Research And Its Application

Soil as an engineering material has very complex properties, such as non-continuous, non-uniformity and nonlinear mechanical. But as a structural body, it also has systematic properties. Every parts of the system are interrelated and coordinated. A series of physical mechanics traits of the macroscopic manifestations are internal microscopic manifestations of the soil. In a certain extent, macroscopic properties of soil are affected by the changes of the microstructure. To get a further understanding of the links between macro and micro, as well as its applications in soil mechanics, many microstructure papers of home and abroad were summarized. And microscopic porosity of soft clay and its influencing factors, the relationship between macro and micro porosity, the average contact area rate and its influencing factors are studied. Some mechanics problems were analyzed by using the relationship between macro-porosity and the average contact area rate. The main research work and results are as follow:(1) Porosity structure characteristics of soft clay were qualitative analyzed by SEM images. Three-dimensional porosity calculation model was built basing on Image-Pro Plus (IPP) software. By calculus ideological, its calculating formula was derived and porosity was quantitative statistics. The relationship between plane porosity of binarization processing and three-dimensional porosity of statistic was also analyzed. The results show, the three-dimensional porosity calculation formula is feasible, comparing with plane porosity of binarization processing, three-dimensional porosity which got from statistic is closer to the real situation.(2) In order to get a reasonable microscopic three-dimensional porosity of soft clay, the influences of calculated step size, magnification, threshold size and analysis area size on porosity results were studied. The results show that, smaller step size is corresponding to a higher accuracy, and step size2can both satisfied the computing capacity and accuracy requirements. It is suitable to choose a magnification of1200±300times to calculate three-dimensional porosity. Threshold value size relates to magnification times, greater magnification should be increased threshold value accordingly. Area of analysis can not be too small, only by choosing over70%of the total area of the image can effectively reflect the entire information of the image.(3) By comparing the relationship between macro-porosity and model calculating porosity, quantitatively percentage of contact area of soft clay has been obtained. The concept of soft clay average contact area rate (Rac) was first proposed. The influences of calculated step size, magnification, threshold size and analysis area size on Rac were studied. The results show that, the Rac is relates to porosity, the more the porosity, the smaller the Rac is. The result is suitable for the objective laws of porosity distribution.(4) In order to get the relationship between soft clay porosity and its contact area rate, soft soil that in Hangzhou, Ningbo, Fenghua were taken to soil test. Many SEM images were got. By using the calculation methods proposed in this paper, the relation equation of porosity and average contact area rate was fitted and got, and its parameter range was studied.(5) Considering the contact area rate of soil in seepage, the new seepage velocity equation was obtained. Critical hydraulic gradient equation of soft clay had got by mechanical model. The seepage force in the exit is consisting of three parts, including seepage force, friction and cohesion. Without considering friction and cohesion, the seepage force equation which considers contact area rate changed into Terzaghi equation.(6) Supposing the soil as solid-liquid two-phase material, a new effective stress equation was obtained by considering soil contact area. The equation was used to consolidation analysis. The Terzaghi one-dimensional and Biot three-dimensional consolidation equations which considering the relationship between macro and micro were obtained.(7) A new water-and-soil pressure divided calculation equation was put forward by considering the soil contact area. The results got from the new equation were smaller than the traditional earth pressure theory. The formula which considering seepage, excess pore pressure were also deduced.(8) A new Swedish slice Method and simplified Bishop Method for slope stability analysis was put forward by considering the soil contact area. The porosity parameters influence on slope stability was studied. By studying the other influence conditions, slop stability analysis equations that consider the slope top overload, buoyancy or groundwater seepage force, seismic force were built combination porosity parameter.