Study On Logistic-Hyperbola Combination Prediction Model For Post Construction Settlement Of Loess High Fill Embankment

Driven by the continuous growth of China's economy,the scale of highway construction is increasing and the technology content is increasing continuously.When constructing highways in mountainous areas,high fill embankments are usually used.The loess is widely distributed in the northwest,the North China Plain and the northeast and south parts of the northeast.In these areas,high embankments of loess high fill are usually used in local conditions.The post construction settlement is the main disease of the high embankment.The settlement of the high fill embankment can be solved,so as to ensure the basic requirements of the highway safety and durability.Many scholars at home and abroad have studied the post construction settlement of high fill embankment,but most of the research is aimed at soft embankment,and there is little research on post construction settlement of high fill embankment.Therefore,it is of great significance to deeply study the law of post construction settlement and related prediction models of loess high fill embankment.In this paper,the Loess High Fill Embankment Engineering in Taihang section of Taiyuan is taken as the research object.Indoor geotechnical test,in-situ settlement monitoring test,settlement prediction model comparative analysis and establishment of combined forecasting model are carried out:1.Laboratory test conclusions of Loess Fill?1?The pore ratio of Loess Fill specimen has the same periodic variation with dry density,and the extreme value appears at 3m and 6m,and the change period is 3m.The reason for the periodic change is that every 3m loess packing is to be rammed.It indicates that the compaction effect of loess compaction is remarkable.?2?The liquid limit value of loess filler is?_L=29.03%,plastic limit value is?_p=20.21%,plasticity index I_p=?_L-?_p=8.82.So the Loess Filler for embankment fill is sandy silt loess.?3?Through the unconfined compression test,compression coefficient3m,4m,5m depth of loess samples were:0.06MPa^-1,0.07MPa^-1,0.08MPa^-1,the compression modulus E_s are:26.37MPa,23.51MPa,20.39MPa,with two sets of indexes,it can be concluded that the Loess at three different depths is low compressible soil.The compression coefficient and compression modulus of loess at the depth of 3m are the smallest and the compression modulus is the largest,which indicates that the compaction effect of the filling body is good at this depth,which proves again that the compaction effect of the heavy tamping method is remarkable.2.In situ settlement monitoring test of high embankment on Loess?1?Settlement,monitoring section of the embankment foundation of loess compression deformation variation,pavement settlement is similar:90 days ago,the settlement grew rapidly,90¹50 days between settlement led to slowdown,affected by the temperature in 150 days,a period of rapid growth of settlement gradually after the convergence,stability.?2?Settlement,monitoring section of the embankment foundation of loess compression deformation variation,pavement settlement is similar:90 days ago,the settlement grew rapidly,90¹50 days between settlement led to slowdown,affected by the temperature in 150 days,the settlement after a period of rapid growth in loess high embankment settlement of the highway is mainly due to the compression deformation of loess subgrade.The loess embankment compression settlement accounts for 90%of the total settlement,settlement of the foundation of the accounting for 10%.There is a positive correlation between the settlement of the Loess Fill and the height of the fill.The greater the height of the fill,the greater the settlement of the fill.Gradually converge and stabilize.?3?The Loess High Embankment in the same section of the early settlement had little difference,but in the late settlement due to various factors?soil particles with high discreteness,geological conditions,groundwater,dynamic load,traffic impact etc.?while significant differences,the same section settlement order on the west side is greater than that of the middle East is greater than.?4?The settlement of loess soil fill is different.The order of settlement of four layers of soil is as follows:third layers of soil are larger than second layers of soil,larger than the first layer of soil is larger than fourth layers of soil.Third layers of soil stress history is short,the consolidation degree of soil is low,the weight and the loads,the soil will be larger compression deformation,settlement of section three layer soil,second layer soil settlement times.The first layer of soil has a long time of self gravity stress,high degree of consolidation,so the settlement is small.In the fourth layer soil,there are 6%lime soil fillers.The strength and stiffness of the soil particles are large,and the compression deformation is the smallest,so the settlement is the smallest.3.Research conclusions of multiple settlement prediction models for predicting the settlement of high embankment in Loess.?1?Using the Logistic model,Hyperbola model,Gompertz model,power model of K4+120 section monitoring settlement numerical fitting,comparative analysis showed the same rule:the prediction accuracy of Logistic model,Hyperbola model,power model is better,can better fit the early settlement of loess high embankment,after 250D,three models has a different growth trend,prediction curve of Hyperbola model,power model,sustained growth and showed no convergence trend,cannot predict the final settlement of embankment,the Logistic model inflection point into the convergence stage at about 250D,but the convergence speed is too fast,can not predict the final settlement,in late three the independent model of loess high fill embankment the settlement fitting errors;although Gompertz model in engineering is widely used for settlement prediction,but the It is proved that the adaptability of the model to the settlement of high embankment on loess high embankment is too poor,and it is not recommended to fit,calculate and predict the settlement of high embankment of loess high fill embankment.?2?The prediction accuracy of Logistic model and Hyperbola model than Gompertz model,power model precision is high,the two models can better fit the early settlement of loess high embankment,good and high embankment in Loess adaptability,but the two model in the prediction of late show different growth trend,therefore,the two is reasonable based on a combination of variable weight combination forecasting model,combines the advantages of the two kinds of independent model.The prediction accuracy of Logistic-Hyperbola combined model is higher than that of the two independent models,indicating that the combination model has better adaptability to the settlement of loess high fill embankment.?3?The final settlement of the three measuring points on the K4+120section can be predicted through the Logistic-Hyperbola combined model,K3X,K3Z,K3D,the final prediction of the settlement are:29.12mm,20.74mm,18.90mm,that is 18.90^K4+120 range of settlement section of loess embankment 29.12mm.