Study On Post-construction Settlement Deformation Laws And Prediction Of High Fill Embankment In Mountainous Areas

Due to the restrictions of line selection and terrain,multiple sections of the Xiasha high-speed road must take the form of fill embankments.And the maximum height of the fill embankments exceeds 60 m.Because high embankment usually has large post-construction settlement and long settlement period,it isprone to experience excessive settlement and uneven settlement,even pavement cracking and shrinkage.Therefore,it is necessary to monitor and predict the post-construction settlement of high fill embankment,which have important practical and research significance for guiding the construction and operation of Xiasha high-speed.Presented in this study are basic physical property test,triaxial test,field monitoring,numerical analysis,theoretical calculation that were systematically and deeply made for the purpose of investigating the physico-mechanical properties of filler soil of Xiasha high-speed A3 contract section and obtaining post-construction settlement monitoring data of high-filled embankment.Then,post-construction settlement law and influencing factors were analyzed.Finally,the post-construction settlement of highfill embankment was predicted from two aspects of numerical simulation and theoretical calculation,and prediction methods suitable for post-construction settlement of high embankment was obtained.The specific research results are as follows:1.The engineering geological properties,physical and mechanical properties of filler soil of Xiasha high-speed A3 contract section.The mineral and chemical composition,the basic physical property indexes,and the influences of water content and compactness on the strength characteristics of filler soil in the study area were preliminary mastered by X-ray diffraction experiment test,chemical analysis test and basic physical and mechanical properties test,which provided strength parameters for later numerical simulation.The study has shown that filler soil is in good gradation,and it meets the engineering filling conditions after certain construction compaction.The triaxial test shows that with the increase of compaction degree of filler soil,the cohesion force and internal friction angle increase.The cohesion force decreases as the water content of the filler soil increases,the internal friction angle increases first and then decreases with the increase of the water content of the filler soil,and reaches the maximum at the optimum moisture content.2.Site monitoring of settlement of high embankment.According to the site actual conditions,the monitoring program was designed to monitor the settlement and horizontal displacement of the high-filled embankment after construction.The monitoring lasted 241 days.The following conclusions were obtained:(1)With the increase of time,the settlement rate of high-filled embankment gradually decreases until it stabilizes.The settlement after 241 days is between 181-191 mm.The different sections of the high fill embankment subside differently,the filling layer subsides most and then the stone filling layer and then the original pavement.And settling time is also different,the filling layer subsides most and then the stone filling layer and then the original pavement.In addition,larger rainfall will accelerate the settlement velocity.(2)After filling the high-filled embankment,slight lateral deformation was occurred under gravity load.The maximum horizontal displacement is about 16.8mm,the deformation is small,so the overall stability of the embankment is better.3.Based on finite element software ANSYS,the post-construction settlement after 241 days of high-filled embankment was calculated,and the influence of compactness of filler soil and rainfall duration on post-construction settlement of high-filled embankment was analyzed.The simulation results showed that the settlement of high-filled embankment after 241 days is about 215 mm,which is larger than the monitoring value,the main reason is as follows:(1)In the process of numerical simulation,the compactness of the embankment was set as a constant(94%),but the actual compactness of the embankment will increase during the consolidation process,and the strength and compression modulus will increase.(2)The size of the simulation model is too large to keep the internal parameters of the model consistent with the real situation.Filler soil compactness and post-construction settlement: with the increase of compactness,the post-construction settlement of embankment decreases sharply first,then the decay rate slows down,and eventually becomes stable.Rainfall accelerates post-construction settlement velocity of high embankments,causing additional settlement of high embankments.4.A variety of calculation methods were used to predict post-construction settlement of high embankments,and the accuracy,advantages and disadvantages of each method were analyzed.Onthe basis of settlement monitoring data,used hyperbola method,logarithmic curve method,exponential curve method,Pearl curve method,NDGM(1,1)model and BP neural network to establish post-construction settlementprediction model,analyzed and discussed parameter selection andthe prediction precision of the model.Then,compared and analyzed theapplicable conditions,advantages and disadvantages of each method.The results show that the performance of exponential curve method and BP neural network are the best,and the prediction error is less than 3%.