Analysis On Pile Cap Effect In Piled Embankment Of High Speed Railway

With the development of high speed railway, piled embankment has been widely used in offline engineerings. Previous studies showed that the two effects above the pile cap (arching in the filling and membraning of geogrid) and the pile soil joint action below the cap are main aspects of working mechanism in this stucture. However, studies nowadays, considering these effects, aiming at optimizing designing and building of high speed railway, are hard to meet the needs of practices. Further study in this field is in sore need and quite worthy.The paper focuses on the effects in piled embankment in high speed railway caused by various rate of coverage of pile caps. First based on the field test, the working mechanism of the structure is analysed. Then the identity element FEM model is established according to the construction. At last, the orthogonal test based on FEM is adopted to analyse the diameter of cap and distance between the piles. Conclusions are:(1)Field test shows:as the main phase of settling,60% of base surface settlement and 85% of relative settlement appears when filling. Arch coefficient varies between 0.22 and 0.24 after filling. The height of arch is deduced at about 1.5m above the cap, equaling to 2.14(s-a). The max strain of geogrid is 0.4%, while the relative strain being 0.1%, telling that the geogrid could be neglected.(2)FEM shows:height of equal settlement plane is 1.5m above the cap, agreed with the mutation height of vertical stress. Arch coefficient is 0.231. Membrane effect is not significant. Large deformation does not affect the settlement, soil stress and strain of geogrid remarkably when calculating; neighter does the interface reduction factor affect.(3)Orthogonal test based on FEM shows:the settlement of soil between piles, rather than that of pile cap, is changed obviously with the increase of pile spacing. The enlarging of cap increases both the settlement of pile cap and the steady rate of soil settlement. Through the range analysing, settlement is more sensitive to diameter of cap, while the arch coefficient is sensitive to them both. The combination of 2.5m in pile spacing and 1.4m of cap diameter in the orthogonal test is superior to that of 1.7m in spacing and 1.0m of diameter adopted in the field test in settlement controlling.