Research On Deformation Properties Of Composite Ground Under Flexible Foundation

Composite ground technology has been widely used in expressway construction. Comparing the composite ground under rigid foundation, the composite ground under road embankment(flexible foundation) has distinct differenence in mechanism, stress distribution and deformation pattern. Nowdays, the research on composite ground under flexible foundation mainly focused on bearing capacity and settlement, but by the reason of such composite ground's work mechanism complexity, it's deformation principle still has many fields needing exploration, especially about it's lateral deformation. In this paper, the settlement and lateral deformation principle of composite ground under flexible foundation was the main research content.In this paper, the total settlement of composite ground was divided into four parts: the settlement of reinforced area, the settlement of underlying layer, the depth of pile top inserting into road embankment and the depth of pile bottom inserting into underlying layer soil. In order to analysis the settlement of reinforced area, setting the proper displacement pattern of DJM piles composite ground under flexible foundation was the first step and, considering the top and bottom of piles inserting into the road embankment and underlying layer soil as well as slide occuring on interface of pile and soil were also necessary. And then, after according Mohr-Coulomb yielding principle to modify the friction stress of pile and soil, the analysis formula to calculate composite ground reinforced area's stress field and settlement was established.The depth of pile inserting into road embankment and underlying layer soil can be resolved according the analysis results of elements stress of pile top and bottom & Vesic ball expansion theory. Depending on the the bottom elememts average stress distribution of reinforced area, the additional stress field of underlying layer area can be calculated. Based on this additional stress result, the settlement of underlying layer area can be solvedd by using layerwise summation method.The lateral deformation of composite ground is always igored in normal ground deformation analysis. But as the up load is road embankment, such flexible foundation's restriction acpability far lower than the rigid foundation, and the lateral deformation will be larger than the composite ground under rigid foundation. In this paper, the reinforced area was regarded as an elastic body and the horizontal additional stress of the reinforced area, which was resolved by using Boussinesq Theory, was looked as the main reason to advance the lateral deformation. Based on the former proposal, the reinforced area was divided into soil and pile elements, and by this way, the lateral deformation of composite ground could be resolved. According to this paper's analysis results, the maximum lateral deformation value was at the composite ground surface under the shoulder of road but not at the toe of road embankment.Finally, by contrasting the calculated settlement result of composite groung and the settlement value from in-site observation in KaiTong expressway project, the credibility of this paper's theory was certificated.