Study On Stability Of Bedrock Loess Fill Slope Under Rainfall

With the promotion of western development and the "Belt and Road" national strategy,the social and economy development of the Loess Plateau area has developed rapidly,and the construction of the new urban area is changing with each passing day,and the scale is large and unprecedented.The vertical and horizontal geographical conditions of the hilly and gully of the Loess Plateau seriously restricts the sustainable and rapid development of the city.For this reason,many cities of the Loess Plateau have carried out large-scale cutting hills to bulid cities and gully land consolidation to solve the contradiction between the special geographical environment constraints and the urban and social and economic development.However,many fill slopes have been formed in cutting hills to bulid cities and gully land consolidation.Excavation and fill interface,bedrock or loess and the filling loess rock and soil media structure have a great influence on the stability of the fill slope,so the stability of the fill slope has become an important issue in the current project of cutting hills to bulid cities and gully land consolidation in the Loess Plateau.Taking the cutting hills to bulid cities in Yan'an New Area as background.Based on the field investigation,data analysis,and indoor geotechnical tests in the Yan'an New Area.The stability of bedrock(I.e.rigid foundation)loess-filled slopes under rainfall in Yan'an New Area was studied through model test and the Geo-studio finite element numerical simulation method,which initially revealed the seepage law and failure mode of bedrock-loess-filled slopes under rainfall conditions,as well as different rainfall methods,fill soil parameters and slope types The influence of parameters on the stability of bedrock-loess fill slope.The results can provide a scientific basis and guidance for the design of bedrock-loess fill slopes and the prevention and treatment of bedrock-loess-filled slopes diseases generated by the construction of cutting hills to bulid cities and gully land consolidation in the Loess Plateau.The main results are as follows:(1)Through collecting data and field geological investigation,the meteorological conditions,hydrological conditions,topography,stratigraphic lithology and other engineering geological conditions of the study area and the failure form of the fill slope under rainfall conditions were identified.Based on the indoor geotechnical test,the basic physical and mechanical parameters of the slope soil in Yan'an New area were determined,which provided the basic data for the establishment of three-dimensional geomechanical model.(2)Based on the indoor rainfall model test,the law of infiltration,deformation and failure of the bedrock-loess fill slope and the failure mode are revealed,as follows:(1)The interface between the bedrock and loess fill slope is the dominant seepage area under rainfall;(2)Under the action of rainfall,the stress in the soil decreases when the slope slides.When the whole slope is unstable,the stress at the interior and the interface rises sharply and reaches a peak value.The amplitude of the increase in the soil pressure at the upper part of the slope is small and the slope foot is large;(3)Under the action of rainfall,the pore water pressure as a whole is stable-rising-declining.When the slope body slides on a large scale,the pore water pressure inside and at the interface reaches the peak,and the pore water pressure at the interface rises earlier than the interior of the slope body.The pore water pressure at the foot of the slope rises the most.(4)The water content in the slope body is stable-rising-steady during rainfall,and the slope is unstable when the whole is saturated;(5)The failure mode of bedrock-loess landslide under rainfall conditions is traction-type shallow landslide failure caused by slope foot instability failure,and the shallow layer of the slope forms a transient saturation zone,resulting in ultra-static pore pressure,and multiple secondary slip surfaces are formed during the failure.(3)Based on Geo-studio finite element numerical analysis,the effect of different rainfall methods,fill soil parameters and slope type parameters on the stability of bedrock loess fill slopes were studied.The result are as follows:(1)The stability coefficients of light rain,moderate rain,heavy rain,and heavy rain all decreased linearly under the rain intensity;under heavy rain conditions,they decreased exponentially.(2)Filled slopes with different degrees of compaction under rainfall The slope stability coefficient increases linearly with the increase of internal friction angle and cohesive force under the action of heavy rain.The internal friction angle has the greatest influence on the slope stability and the cohesive force has less influence;(3)The stability coefficient increases with higher permeability coefficient Rainfall declines linearly and...