Research On Embankment Load Transfer Mechanism And Parameters Optimization Of Road Embankment Supported By Rigid Piles

In this paper, soft soil foundation supported by rigid pile under roadembankment is studied. Pile-net composite foundation and piled embankment arechosen test objects. Through field tests and simulate calculation, the load transfermechanism of road embankment is analyzed. Characteristics of the two treatments arestudied through a more reasonable analysis model and improved formulas.Meanwhile, the design parameters of each treatment are optimized. The maincontents of the research are as follows:①Pipe pile test section is set in GuangWu expressway, and soft soil foundationsupported by PHC pipe piles is studied through field tests, which are carried out infour different conditions, two of them are pile-net composite foundation withdifferent cushions and the other two are piled embankment with pile caps anddifferent cushions. Based on the pore pressure and settlement data of differentsections, soil arching and failure mechanism of embankment are discussed. Pile-soilcooperation process can be divided into two phrases, whose division point is the peakvalue of pile-soil stress. Stress ratio of pile to soil and beating capacity of the pile andsoil are obtained through data processing. And characteristics of pile and soil stressand load transfer mechanism of each treatment are studied. The proposals of designand construction of soft soil roadbed reinforced by pipe piles are proposed.②To explain the deformation and stress characteristics in the field test, wholeworking models are built for pile-net composition foundation and piled embankmentrespectively. As to pile-composition model, 'sliding piercing model' is built, whichcan well explain the intermittent piercing of piles. For piled embankment,'compaction arch' model is put forward, which consider the steady basic structure tobe an arching whose spring is the pile top. The model can well explain thecharacteristics of stress and settlement of the piled embankment in the tests.③Calculation model for the load transfer of embankment is built by FLAC^3D,and three-dimensional perspectives of displacement and stress are plotted. Accordingto the perspectives, principle stress and displacement in the embankment are analyzed,and distribution of arching effect is obtained. The in being calculation models andmethods are summarized. The 'rigidity core arch model' is put forward. Formulas forload transfer ratio and stress reduction ratio are derived based on Hewlett method.The calculation results of each method are compared with the filed test results, andthe 'rigid core arch model' is reasonable. ④Presently, pile-net composition foundation and piled embankment can not bewell distinguished, and the field test items are insufficient, so the stress-strain relationof pile and soil can not be fully understood. To meet this problem, calculation modelsfor pile-net composition foundation and piled embankment are built respectivelyusing the numerical model analysis software, FLAC^3D, and are verified byobservational data. The deformation characteristic of soil mass at pile-top limitingsurface and pile stress of the two treatments are distinguished. The total settlement ofpiled embankment is less than pile-net composition foundation, and reduced by about2/3. The pile axial force of the two treatments is nearly the same. Negative friction onpiles exists in pile-net composition foundation, and the maximum value of the axialforce is at the position of 3/5 pile length below pile-top, while the negative skinfriction in piled embankment is so smaller that the maximum value of the axial forceis at the position near pile-top. The shear and moment of out piles in piledembankment is bigger than pile-net composition foundation, so a higher strength ofout piles is needed. In conclusion, the treatment effect of piled embankment is betterthan pile-net composition foundation, while pile-net composition foundation is easierto construct and more economical.⑤Through the distinguishing between pile-net composition foundation andpiled embankment, parameters optimization of each treat method are done. Forpile-net composition foundation, numerical tests are done by changing cushionparameters and pile spacing. For piled embankment, numerical tests are done bychanging cushion parameters, pile spacing and pile cap. Results show that, as topile-net composition foundation, a higher module and internal friction angle ofcushion filling, as well as a thicker cushion will reduce the relative displacement ofsoil, then a better reinforcement effect will be obtain. A proper value for cushionmodule is 80MPa～150MPa, and a filling with high cohesion is adoptable, pilespacing should be no more than 3.0m, and 2.0m～2.5m is advisable. For piledembankment, cushion is necessary. The advisable pile spacing is still 2.0m～2.5m,however the treatment effect is better than pile-net composition foundation when thepile spacing is the same. The optimal area ratio of pile area cap to total area is 0.25when pile spacing is 2.0m～2.5m.