Load Transferring Rules And Settlement Calculation Of The Gravel Pile Composite Ground Under Embankment Loads

With the composite foundations widely used in civil engineering, the relevanttheoretical research has also been continuously developed and improved. As one ofthe treatment technology, the gravel pile composite foundation is applied to treat thesoft foundation in expressways. Although there are quite some research work areavailable on this kind of composite foundation, such as studies on the bearingcapacity and settlement calculation, the understanding of its reinforcementmechanism and bearing capacity deformation properties is not deep enough. Forexample, under the vertical load, relative slipping will exit on the pile-soil interface,and the radical deformation will occur to gravel piles in the shallow subsoil region,which will result in a complicated bearing behavior of the pile shaft instead of thetraditional equivalent-strain model. Therefore, it is essential to explore and establish amodel suited to the actual conditions. At the same time, how to exactly calculate thesettlement of gravel pile composite foundation under embankment load has becomethe key point and difficult problem of the current research. Based on summarizing andabsorbing the previous research results, analysis method of calculating the settlementof gravel pile composite foundation under embankment load is studied further in thispaper. The main work is listed as follows:(1) Based on the available achievements, the consolidation behavior, deformationmechanism and failure modes under vertical load of gravel pile composite foundationwere first discussed in detail. Then, a few common calculation models to calculate thebearing capacity of gravel pile composite foundation under embankment load weresummarized.(2) By introducing more appropriate vertical and radial deformation models, andtaking such factors into consideration as the neutral point of pile side frictiondistribution, bulging deformation of the gravel pile and pile-soil interaction, thecontrol equations of inner forces and displacement of pile bodies under embankmentload were set up. Then, the analytical solutions of pile side friction resistance, pilebody stress and the additional stress distribution of surrounding subsoil were derivedrespectively. On this basis, by introducing corresponding boundary conditions,simplified formulas to calculate the compression deformations of the pile shaft andthe reinforcement region were obtained with the determining methods of the necessary parameters presented as well.(3) Finally, combined with an engineering example, comparative analysis wascarried out. The results show that, the composite modulus method overestimates theeffect by the pile shaft. Without considering the radical deformation of the gravel pile,calculation result of the settlement is less than the actual value. As the analysis modelin this paper considers the bulging deformation of pile shaft, the pile-soil interactionand the neutral point distribution of pile side friction, the result by the present methodis more in line with the stresses and deformation characteristics of practicalengineering than the composite modulus method. Through a further parameteranalysis, the distribution laws of pile body stress and the side friction in the gravelpile composite foundation under embankment load were found out. And influencingrules on the gravel pile composite foundation under embankment load by theembankment height, modulus ratio of pile to soil, the pile soil Poisson’s ratio and areareplacement ratio were discussed respectively.