Study On Stability Analysis And Control Of Expressway Slope Subgrade Under Seismic Conditions

In the construction of expressway in the mountainous plateau area of Yunnan,Guizhou and Sichuan,the proportion of slope subgrade accompanied by high fill is relatively high,but the seismic activity is frequent in this area,which not only brings troubles to the design and construction of slope subgrade,but also makes the stability control of slope subgrade more difficult under seismic conditions,and poses a serious threat to the later safe operation.Based on the Yibi Expressway Project from Yibin in Sichuan Province,through Zhaotong in Yunnan Province,to Bijie in Guizhou Province,this paper takes the high fill slope subgrade of expressway as the research object,the dynamic analysis model of slope subgrade of expressway is established on the basis of the analysis of slope engineering geological conditions,the slope subgrade under seismic conditions is calculated by GeoStudio numerical analysis software,and the slope subgrade under seismic conditions is also analysed.The influence of seismic horizontal acceleration,slope gradient,embankment filling height,filling-excavating ratio and other factors on the dynamic response and stability of subgrade is studied,and the reinforcement measures of subgrade slope and subgrade are analyzed.The main research contents and achievements are as follows:(1)Based on site engineering geological conditions and seismic characteristics,a dynamic analysis model of slope subgrade considering slope gradient,filling height and filling-excavating ratio is established,which lays a foundation for dynamic response and stability analysis of expressway slope subgrade under seismic conditions.(2)The dynamic response of slope subgrade with different slope gradient,filling height and filling-excavating ratio under different seismic horizontal acceleration conditions is calculated.The analysis results show that:With the increase of seismic horizontal acceleration,slope gradient,fill height and fill-excavating ratio,the dynamic response of slope top of slope subgrade,such as peak acceleration,velocity and displacement,increases in varying degrees.There are two critical filling heights.With the increase of filling height,the acceleration decreases when the filling height is lower than the first one.The acceleration amplification effect increases when the filling height is between the two heights,and decreases when the filling height is higher than the second one.The acceleration amplification effect on the downhill slope is greater than that on the uphill slope,and the greater the slope gradient,the more significant it is.The peak acceleration amplification effect on the downhill slope of 22 degree slope embankment can reach 6.4 times of that on the uphill slope.(3)The safety factor and permanent displacement of the slope subgrade slope and the subgrade under various working conditions are calculated,The analysis shows that:Quasi-static safety factor,minimum average safety factor and permanent displacement are used together to evaluate the stability of slope subgrade under seismic conditions,which is more reliable and reasonable.With the increase of seismic horizontal acceleration,slope gradient,filling height and filling-excavating ratio,the stability of slope subgrade decreases on the whole,but exist the stability increases with the increase of slope gradient or filling height,with an increase of about 5%.(4)Typical sections of slope subgrade are selected for reinforcement.It is found that dense reinforcement in the middle of slope subgrade slope and dense reinforcement in the lower part of slope subgrade surface are more conducive to improving stability.When the amount of reinforcement is equal,the safety factor of dense reinforcement in the lower part can be increased by 4%and 2%respectively compared with that in the upper part and the middle part.