Model Test And Numerical Simulation Of Piled Embankments With Analogical Soil Fillings

With the national regional and integral economic development,inter-city rapid railway lines and national high-speed railway network which is suitable for national conditions is planning and under large-scale construction.The railway network is becoming more and more concentrated.The original place with bad geological conditions(dredger fill,organic soil,expansive soil and other high-compression or medium compressed soil)which should not be considered as engineering embankment will inevitably be planned for high-speed railway route.Pile-supported embankment has great advantages in increasing the bearing capacity of foundation,controlling construction settlement,post-construction settlement and uneven settlement.It has obvious advantages in construction speed and economic benefit as well.The study of piled embankment is also making brisk headway.In recent years,more and more attention is paid to the embankment deformation and soil arch evolution.The project group developed a multi-trapdoor test box installation which can model how the pilesupported embankment works.The model tests of piled embankments use elliptical steel rods as the embankment fillings.Particle Image Velocimetry(PIV)technique was adopted to achieve the whole deformation and several load cells were used to measure the load distribution under the fill.In the test group,the parameters such as the pile spacing,pile width and packing height were adjusted to obtain the deformation regularity of embankment evolution under different conditions.And then another test group was carried out under the reinforced condition.The similarities and differences between the reinforced condition and the non-reinforced condition were analyzed,and the effect of the reinforcement parameter change on the load transfer and the soil arch structure was researched as well.In order to observe the regularity of the load transfer mechanism in the embankment,the numerical model corresponding to the model test is established,and the force chain in the simulation is observed to show the development of the soil arch structure.Get the following conclusions:(1)Steel analogical soil filling has similar characteristics with slightly dense sand.it can reflect the peak intensity and dilatancy of sand,but it has lower actual coefficient of friction and irregularity than sand filling.(2)The evolution patterns of piled embankment with steel analogical soil have three types: triangular expansion pattern,tower-shaped evolution pattern and equal settlement pattern.All evolution process begins with the initial triangular,and the height of the packing,the spacing between the piles and the width of the pile determines the type of the embankment arch.(3)In the three evolution patterns,the pile-soil stress ratio of the equal settlement pattern is the largest,and the ratio decreases less than the other two patterns after the peak.This reflects that the soil arching effect of equal settlement pattern is the highest and most stable.(4)After the reinforcement adopted,the settlement of the fillings is limited,and the uneven settlement and settlement are reduced.The types of soil arch evolution include equal settlement pattern and non-equal settlement pattern.The equal settlement pattern of reinforced steel analogical soil filling embankment has a uniform displacement surface.It is suitable for practical engineering.(5)The final settlement of the grids in reinforced embankment test is positively correlated with the net pile spacing and negatively correlated with the geo-grid strength,it has no connect to the pile width and its relationship with height of the filling is not significant.The efficiency of load transfer is closely related to the final settlement of geo-grid.When the settlement approaches the final value,the grid's tensioned membrane effect play a leading role,and load transfer efficiency grows rapidly.(6)The reinforcements have effects on the soil arching effect of the embankment,which may be caused by the decrease of the displacement between the pile and the soil.The practice of placing the geo-grid on top of the pile can maximize the tensioned membrane effect and reduce the effect on soil arching,it can improve the efficiency of embankment load transfer as well.(7)The results of numerical experiments are similar to the model tests.Numerical simulations can simulate the stress-strain characteristics of model tests and reflect the evolution of piled embankment under indoor test conditions.The force chain evolution of the embankment in numerical test is obtained,and the process of the "soil arch structure" evolution can be described as "development-stability-destruction and reconstruction".