Stability Analysis Of Loose High Slope Under Excavation Unloading Condition

China is one of the countries with the most serious geological disasters and the most threatened population in the world,especially in southwest China,landslides,debris flows and other geological disasters occur frequently for a long time.The frequent tectonic activities in the region,coupled with the physical and chemical processes such as valley downcutting,weathering and dissolution,make the loose accumulation layer slopes widely distributed in southwest China.This kind of natural slope is generally in a stable state under natural conditions,but once the engineering construction is excavated,the stability of the slope will be greatly affected,and some slopes will be unstable and sliding during the construction process.It seriously affects the safety of engineering construction.This paper is in combination with the long-term engineering site.On the basis of investigation and reference to the previous research data,taking the slope excavation of the project under construction in Songkan area of Tongzi County,Guizhou Province as the research object,the regional geological environment conditions and the main diseases existing in the process of slope excavation are consulted and analyzed.The deformation and failure characteristics and instability mechanism of loose slope excavation are investigated and studied.on this basis,the stability change,displacement and the development of plastic zone in the process of slope excavation are calculated by GEO-Studio.FLAC3D simulation.The main conclusions are as follows:(1)The study area mainly belongs to the humid subtropical monsoon climate.with concentrated precipitation and abundant rainfall.Based on the analysis of rock and soil mass and its unique structure in Songkanzhen area and the long-term on-site investigation,it is concluded that there are four main diseases in the excavation process of loose high slope,including instability landslide,slump failure,slope surface spalling and mud flow.(2)The excavation destabilization of loose high slope mainly occurs in the shallow surface of the slope.According to the composition of rock and soil,the content and structure of gravel,it can be divided into landslide and slump.When the content of gravel is small,the size of gravel is small,and the structure is suspended in gravel soil with large size,the failure of landslide occurs;when the content of gravel is large and the size of gravel is small,the failure of landslide occurs.Larger,the structure is large-size block stone forming skeleton,which is filled with gravel soil,and then it shows slump failure.(3)Among the I#and 3#slopes,the cracks with length between 10 and 20 m are the most developed,which are the dominant length intervals,accounting for 34.48%and 40.54%of the cracks in the two characteristic loose slopes,respectively.When the width of cracks exceeds 10 cm,the slope is likely to be destabilized,which provides a statistical theoretical basis for monitoring and early warning of construction and excavation of loose high slope to a certain extent.According to the deformation and failure characteristics of the loose high slope during excavation,the evolution mode of the unstable failure of the loose high slope during excavation can be divided into two types:creep-pull-slip,sliding-pull-slip.(4)The influence of excavation on loose high slope is one of the important factors affecting its slope stability.Under natural conditions,the slope stability coefficients are 2.062,1.117 and 1.015.The slope stability coefficients are reduced by 45.35%-50.68%by excavation,1.892,1.013 and 0.773 by rainstorm,and the slope stability coefficients are reduced by 55.98%-59.14%by excavation.(5)Excavation disturbance and rainfall are two main factors affecting the stability of excavation of loose high slope.These two factors interact with each other,and the coupling effect becomes more and more obvious with the excavation of slope.The stability coefficient decreases by 4.93%-8.24%in the case of no excavation,9.31%-11.92%in the upper stage after excavation and 22.485%-23.99%in the case of the third stage after excavation.(6)The simulation results show that the loose slope is disturbed and displaced in a large range after excavation,and the stability of the slope is significantly affected by excavation.Large displacement occurs at the fifth grade edge and middle and lower parts of the slope.The top of the slope belongs to the tension and crack deformation after excavation,and the middle and lower part is the bulging area during the stress adjustment of the slope after excavation.When the excavation height of the slope reaches 10m,the slope will enter an under-stable state.After the excavation of the upper three levels of the slope,the slope will be destroyed.