Study On Road Loess Slope Stability Under Heavy Rainfall Based On Water-air Two Phase Flow Theory

The vast geological situation of our country is complex,and most of the central and western regions are plateaus,mountains and hills,so road slope engineering is inevitably involved in the process of road construction.Whether the slope is stable or not directly determines the safe operation of the road,so the research on the stability of road slope is a very important topic.Rainfall is an important factor leading to road slope instability,many researchers focus on this,to explore the relationship between rainfall and slope stability.At present,there are many related studies,but most of them ignore the influence of pore air.When the rainfall intensity is large,ignoring the influence of air may overestimate the total amount of Rain Water infiltrated into the slope,and then underestimate the stability of the slope is not conducive to the follow-up slope treatment,resulting in a waste of human,material and financial resources.Considering the influence of pore air on infiltration,the slope infiltration can be analyzed more accurately and closer to the actual situation.The slope safety factor calculated based on the infiltration results is also more accurate,which provides reliable information for slope treatment.Based on the theory of water-air two-phase flow and Geostudio software,this thesis evaluates the influence of pore air on the infiltration and stability of loess slope by comparing and analyzing the infiltration and stability of single-phase model and two-phase model.First of all,the definition of heavy rainfall is defined,and then the corresponding time when pore air begins to affect infiltration is discussed,and then the changes of loess slope stability in different rainfall intensity order phase model and two-phase model are compared and analyzed.Then the influence of soil hydraulic characteristic parameters on slope stability under the influence of pore air is studied.Finally,the loess slope of a road in northwest China is selected to compare and analyze the stability of the slope under the condition of heavy rainfall.The main work and conclusions are as follows:(1)The definition of heavy rainfall is defined.The rainfall intensity which is greater than the permeability coefficient corresponding to soil saturation 0.9 is defined as heavy rainfall.When the rainfall intensity conforms to the definition of heavy rainfall,the effect of pore air on infiltration must be considered.In addition,under the condition of heavy rainfall,the anti-seepage effect of pore air does not begin with the beginning of rainfall,but begins to be reflected when the surface layer of loess slope reaches high saturation.It is found that the greater the rainfall intensity of the soil is and the higher the initial saturation is,the earlier the impermeable effect of pore air is reflected.(2)The stability changes of loess slope under different heavy rainfall conditions are compared and analyzed.In the single-phase model,the decrease of slope safety factor increases with the increase of rainfall intensity.In the two-phase model,with the increase of rainfall intensity,the decrease of slope safety factor is obviously smaller than that of single-phase model.This is due to the fact that the impermeable effect of pore air weakens the effect of rainfall intensity on stability.(3)Under the influence of pore air,the infiltration conditions are studied when the air-entry value a,saturated volume water content θs,residual volume water content θr and saturated permeability coefficient ks are changed.The results show that in the single-phase model,the deeper the infiltration depth of Rain Water is,the greater the decrease of slope stability is with the increase of a,θr and ks values and the decrease of θs values.It also shows the same rule in the single-phase model,but the decrease is smaller than that in the single-phase model.This is mainly due to the influence of pore air,which hinders the infiltration of rain water.(4)Taking a loess road slope in Northwest China as an example,the slope stability of single-phase and two-phase models under extreme rainfall conditions is compared and analyzed.Under the influence of pore air,the slope safety factor of the two-phase model is significantly higher than that of the single-phase model after the end of rainfall,indicating that pore air is beneficial to the stability of the slope under the condition of heavy rainfall.