Study On Multi-Scale Seepage Of Unsaturated Soil And Its Effects On Stability Of Soil Slope

Unsaturated soil is widespread in nature,the seepage and stability analysis of which have been a reach focus in geotechnical engineering.The soil medium,meanwhile,is a typical porous material with multi-scale structure.And in recent years,analysis concerning its seepage characteristics from different scales has attracted more and more attention.Using analysis programme programed by FORTRAN language,the paper has carried out some analysis about the seepage and stability of unsaturated slope through a multi-scale model by introducing several multi-scaled parameters and combining with a project example.At last,some studies about the dilatancy of unsaturated soil slope and its effects on the stability of soil slope have been carried on.The specific research content are as follows:(1)This paper completed the seepage boundary of the finite element program:water head boundary condition and flux boundary condition..On the basis of saturated-unsaturated seepage field,stability analysis has been carried out.Numerical results about water level fluctuation disclose that the evolution of slope stability is effected by the evolution of unsaturated zone and the water pressure.And under the same range of water level decline,rapid decline leads to a fast drop of FOS.(2)Researches about the effects of different forms of Bishop effective stress parameters reveal that the order of size of computed FOS is:Vanapalli,Alonso,Fredlund,Oberg,Sun.The following researches are about the contrastive effects when including additional strength caused by matric suction to equivalent normal stress and equivalent cohesion.After completing the calculation of equivalent cohesion in integral point of stability analysis,the following works contrasted its effect on stability of slope with unit equivalent method.(3)Proposing a multi-scale infiltration model of unsaturated soil by choosing coefficient of variation,macro-pore area ratio and the rock content as multi-scale factors and completing their program implementation,this paper shows the influence of this model on seepage field by several examples.Based on the multi-scale infiltration model,analysis has been carried out about a landslide accident occur in Guangming new district of Shenzhen.Simulations about original slope body under several working conditions display:short intense rainfall has an obvious impact on the stability of slope and caused the rapid decline of FOS,and drainage by blind ditch can increase the FOS of slope,and infiltration caused by top seeper has a negative influenceon the stability of slope.(4)This paper analyzed the effect of dilatancy on the stability of slope.Using Davis equivalent formula,non-associated plastic materials can be equivalent to associated plastic materials before carrying out the stability analysis.And some analysis have been done about the dilatancy of horizontal layered soil,results display that compared to the upper layer,the dilatancy of lower segment of soil has more significant impacts on whole stability,and the volume of soil layer has more remarkable influence on the FOS than the position of soil layer.