Air Resistance Effect And Deformation Law In Unsaturated Seepage Process Of Slope Under Rainfall Conditions

Our country is seriously affected by geological hazards,especially in the southwest of China.Because of the complex geological conditions and heavy rainfall,various geological hazards have brought about great loss of life and property.Among all kinds of geological hazards,slope instability induced by rainfall is the most common form.The change of slope stability caused by rainfall slope infiltration is the key problem.Therefore,the analysis of the infiltration process of slope under rainfall conditions is helpful to understand the slope failure.Most of our research objects are unsaturated soils.In this case,the infiltration process is different from the saturated seepage which we usually study.The characteristics of unsaturated seepage are due to the unsaturated characteristics of soil and the gas resistance effect.In view of this situation,this paper studies the unsaturated seepage and air-resistance effect under rainfall conditions and the deformation characteristics of slope,and analyses the interaction of various phenomena,so as to obtain the infiltration process of slope under rainfall conditions and the influence of air-resistance effect on slope stability.The results show that:1.Generally,slopes are unsaturated in engineering practice.The interaction of gas and liquid phases in soil pore affects rainfall infiltration,slope stability and failure forms.Therefore,it is necessary to consider the matric suction,water content and permeability coefficient of unsaturated soils by using SWCC and HCF to expand the single-phase flow to two-phase flow.2.The factors control infiltration under rainfall conditions should consider the combined influence of gravity,matrix suction and air resistance.During rainfall,the infiltration process can be divided into 3 stages:matrix suction control stage,matrix suction+gravity control stage and gravity control stage.The effect of gas resistance can be divided into two parts:residual bubbles and frontal air pressure.The residual bubbles reduce the saturation of seepage zone.The frontal air pressure acts on the front of wetting front.3.Based on the Mein-larson infiltration model,we consider three infiltration control factors and expand the Mein-larson infiltration model.In order to consider the effects of gas resistance on residual bubbles and closed air pressure,the permeability coefficient K(7)?(8)is related to residual bubbles(water content).The closed air pressure is based on the relationship between rainfall intensity and saturated permeability coefficient,the air entry value and the depth of soil layer.We propose characteristic headh_f.4.We carried out one-dimensional soil column infiltration model test and numerical simulation.Through the research in this chapter,we analyzed the one-dimensional infiltration law under the same condition of the slope rainfall.Infiltration rate is controlled by transient depth Z_n and gas resistance effect in seepage area.The influencing factors of gas resistance effect include the relationship between rainfall intensity and saturated permeability coefficient of sand,and transient depth Z_n in seepage area.In this paper,the rainfall intensity is less than the saturated permeability coefficient of sandy soil.As the depth increases,the release channel decreases and the gas resistance effect gradually becomes obvious.When the wetting front reaches the bottom boundary,the"rebounding effect"appears.5.Observing and analyzing the wetting front,water content,matrix suction and pore pressure in slope rainfall model test,the infiltration law of slope is revealed.The pore pressure curve can be divided into four stages:the pore air pressure rising stage,the relative stabilization stage,the rebounding stage and the pore water pressure dissipating stage.Compared with one-dimensional soil column infiltration,slope model test has unique characteristics because of geometry(slope thickness,slope angle),slope size and underlying bedrock.6.The main factors leading to slope deformation during rainfall infiltration include the contractile skin,slope consolidation and lateral sliding of slope along bedrock surface.The development of horizontal and vertical deformation at the crest and middle of slope shows two stages at the characteristic time point(the time when the wetting front reaches the bedrock surface),and the deformation reaches its peak soon after the wetting front reaches the bedrock surface.7.Infiltration and deformation is a interactive process.On the one hand,we know that the increase of pore air pressure during rainfall is caused by the decrease of pore volume due to the downward movement of wetting front and consolidation deformation.On the other hand,slope deformation leads to the increase of slope density,which has two effects on soil-water characteristic curve:the increase of density reduces the permeability coefficient of soil and the increase of air entry value of soil.In the early stage of rainfall,the unsaturated seepage process of slope is beneficial to the prediction and study of slope instability.It provides us with a new way of thinking in slope treatment and summarizes the relationship between infiltration and deformation.Because of the interaction between them,we can use capillary barrier and improved permeability coefficient to control the infiltration process.By reducing the effective infiltration amount,we can control the infiltration process.To reduce the influence of rainfall on slope stability.