Research On Reliability Analysis Of Loess Cutting High Slope Of Yan’an East Ring Expressway Study

China is one of the most widely distributed areas of loess in the world.As a typical area of loess distribution,Yan’an area has a large number of deep excavation cutting slopes in infrastructure construction projects such as expressways.Due to the special properties of loess and numerous stratigraphic divisions,the spatial variability of slope soil strength parameters is large,which affects the accuracy of parameter determination.Therefore,the stability and reliability analysis and evaluation of loess slope has become the key research content in engineering.Based on the slope engineering of Yan’an East Ring Expressway,this paper studies the slope type design and reliability of the high loess cutting slope of the project,and determines the slope failure probability and reliability index with the Loess Strength Index of the slope in the project area as the analysis parameter.The main conclusions of this paper are as follows:(1)Consult the research methods,research contents and development status of loess slope stability and reliability at home and abroad,and determine the slope shape design content and reliability analysis idea of loess cutting high slope.(2)This paper expounds the general situation of the project slope engineering,and makes it clear that the Loess in the project area is mainly Malan loess layer and Lishi loess layer;The point statistical method is used to count the physical property indexes and strength parameter indexes of loess in the project area.It is concluded that the water content,cohesion and internal friction angle of loess property indexes in the project area comply with the linear change law along the depth direction.Further inspection shows that the distribution of cohesion and internal friction angle indexes in Loess Strength Parameters comply with the normal distribution law.(3)Through engineering analogy and stability calculation,it is concluded that the designed comprehensive slope rate of loess cutting high slope is 1:1.20～1:1.35,and the slope stability coefficient is required to be greater than 1.25;In Malan loess and silty clay layer,the single-stage slope ratio is 1:1 and the single-stage slope height is 8m;In Lishi loess and hard plastic silty clay layer,the single-stage slope rate is 1:0.5,and the single-stage(4)slope height is 3～5m;The width of stepped slope platform is 3～5m,and 2～3wide platforms with a width of 6～10m can be set as required.(5)The basic concepts of reliability analysis are introduced.It is clear that the reliability analysis method can take into account various uncertainties in slope engineering and reflect the failure of slope;The principles and steps of three reliability analysis methods,first-order second moment method,point estimation method and Monte-Carlo method,are discussed,including cohesion(c)and internal friction angle of soil strength parameters(φ)And its coefficient of variation(δc)、(δφ),It is the most important variable affecting slope reliability.(6)The results of three reliability calculation methods are analyzed,and it is clear that when the variation coefficient of strength index is combined with δc=0.3,δφ=0.15,the corresponding slope failure probability is about 10%;For the case that the combined mean value of loess strength parameter variation coefficient of the whole line of the project isδc=0.15,δφ=0.08,and the combined mean value of loess strength parameter variation coefficient of 6 slopes with different slope heights is δc=0.12,δφ=0.04,and the difference of loess strength variation coefficient is less than the combined δc=0.3,δφ=0.15,that is,the failure probability of the project slope is less than 13%,which meets the requirements of loess cutting high slope for reliability.