Optimal Scheme Of Loess Fill Slopes And And Its Application In The Hilly Areas With Low Height And Gentle Slopes In Lanzhou City

The design of fill slopes is one of the important tasks in the field of geological engineering.Designing safe and economical fill slopes has always been one of the hot topics in the field of geological engineering.Lanzhou city is restricted by topographic conditions,land resources are scarce.Engineering practices including land reclamation(removing mountains)are started for city sprawl in 2008.The loess slopes which are constructed by removing the mountains are distributed in the hilly areas with low height around the city.The safety and stability of loess fill high slope formed in the project is one of the most concerned problems of the local government.Therefore,the research on the optimal scheme of high loess slope has significant theoretical significance in the field of geological engineering,and has a more important practical value for construction in Lanzhou city.720 loess fill slopes with different compaction degree,slope height,slope of gully,platform height and platform width,slope rate are designed by uniform test method according to the characteristics of loess high slope in land reclamation(removing mountains)area.The safety scheme and dangerous scheme of slope are obtained by calculating the stability of loess fill slope under different working conditions based on the coupling of SEEP/W and SLOPE/W modules in GeoStudio.The optimal filling scheme of loess fill slope is determined based on the safety and economic principles.The safe slope envelope surface and dangerous slope envelope surface of loess fill slope are determined by using Matlab tool.The slope stability of the loess in the Taipingyang site was evaluated,and Flac3 D which is a finite difference numerical simulation software was used to predict the failure deformation modes and damage conditions of the dangerous fill slope in the Qingbaishi site.(1)It needs 720 trials when platform height,slope rate and platform width of different compaction degree of filled soil,slope of gully and slope height are designed through the uniform experimental design method,and even if the parameters are encrypted near the stability factor,the number of trials is greatly reduced compared to the full 7920 trials.(2)The rainstorm condition with the greatest influence on slope stability is obtained through the SEEP/W module of GeoStudio and the stability under the present condition,the heavy rain condition and the earthquake condition are evaluated though the SLOPE/W module.It is concluded that the earthquake has a great influence on the stability of the slope,and the influence of rainstorm on the stability of the slope is small.(3)The slope shape parameter and the single-width fill amount corresponding to the target stability factor can be searched using the uniform test design,and then encrypting the slope shape parameter of the target stability factor,the different slope shape parameter combinations of the dangerous and safe boundary can be searched out.And the optimal filling scheme can be searched out.(4)Using MATLAB to fit the slope parameters of the target stability coefficient boundary,dangerous and safe envelope surfaces can be obtained.According to the safe envelope,it is suggested that 90% and 95% degree of compaction should be adopted for the slope which is above 90 meters height,and the 80% degree of compaction is recommended for the slope which is below 60 meters slope height.(5)When the compaction degree,slope height and slope of gully are certain,the sensitivity of the slope parameters to the stability of loess fill slope is platform width,slope rate and platform height in turn.The stability increased significantly with the increase of platform width,and the stability decreased with the increase of slope rate and slope height.(6)The quantitative evaluation of the fill slope in the Qingbaishi site shows that the slopes of section 1-1,3-3 and 5-5 are basically stable or stable in both natural and rainstorm conditions,and the slopes of 1-1,3-3 section are in the basic stable state in the earthquake condition,and the slope of 5-5 section will be unstable under the earthquake condition.The results of qualitative and quantitative evaluation are basically the same.The reliability of the qualitative evaluation is determined by the slope parameters.The closer the parameters to the ideal fill model,the more accurate the results will be.On the contrary,it can only be roughly evaluated,and the reliability of the evaluation results will be reduced.(7)Analyze the deformation and failure pattern of 5-5 fill slope under earthquake condition.The unstable slope body will run through the loess layer of the original slope,resulting in deep sliding and cutting out from the foot of the slope.So the instability of the slope has nothing to do with the filled soil under earthquake condition.But it is related to the original nature of loess slope and slope shape.