Application Research Of CFG Pile In Road Soft Soil Foundation Treatment

With the rapid development of economy in coastal areas,urban road construction has been experiencing astounding advances.Fujian coastal soft soil foundation has its own characteristics compared which is different from that in mountainous areas and inland plain areas,such kind of soft soil is quite deep and special that the main soil layer is marine silt with high water content,large porosity ratio and low compression modulus,thus its natural foundation has low bearing capacity,large compressibility and poor mechanical properties.Moreover,the bearing capacity of road foundation cannot be met in road construction which makes the study of soft soil foundation treatment in coastal areas of Fujian a representative technical problem in urban road construction.Nowadays,the utilization of cement fly-ash gravel pile(CFG pile)composite foundation has been used mature.This kind of foundation is widely used in road engineering due to its merits of high bearing capacity,small settlement,low cost and short construction period.This paper studies the CFG pile composite foundation of Houpu Road construction project in Fuzhou city and the main work is as follows:Firstly,the geological condition of the project is analyzed,then the model of natural foundation and CFG pile composite foundation are established according to its design scheme by using ABAQUS software,in addition,the road bearing capacity and settlement values calculated by finite element are extracted to analyze the defects of natural foundation and the advantages and mechanism of CFG pile composite foundation;Secondly,participate in the construction of CFG pile composite foundation and extract the settlement monitoring data after the completion of the project,then the obtained data are compared with the results of finite element calculation to verify the rationality of finite element calculation;Finally,ABAQUS software is used to establish different models for calculation,and the influence of four parameters including pile length,pile diameter,pile spacing and cushion thickness on bearing capacity and ultimate settlement of CFG pile composite foundation,in addition,three parameters which are pile length,pile spacing and cushion thickness are combined to optimize the parameter selection of CFG pile composite foundation in this project.The main research results are as follows:(1)The CFG pile composite foundation model is established by ABAQUS software,and the result obtained by the model is close to the theoretical calculation value and the field monitoring value.The model can be used as a practical reference.(2)The increase of pile length and pile diameter can increase the foundation bearing capacity and reduce the settlement of CFG composite foundation.However,when the pile length and pile diameter are large enough to a certain value,the effect trend on the foundation becomes smaller;The reduction of pile spacing can increase the bearing capacity of foundation and reduce the settlement amount of CFG composite foundation,but the number of piles must be made up and as the pile spacing decreases,the decreasing trend of settlement of composite foundation also diminishes.(3)By calculation,the selected thickness of the bedding in this project is between 258mm and 571mm.The bearing capacity of CFG pile composite foundation will not be affected by the change of cushion thickness.When the cushion thickness is between 300 and 500mm,the larger the cushion thickness is,the larger the settlement of CFG pile composite foundation will be.(4)Based on the cost of pile and cushion in the market,the cost of different schemes is calculated.Through comparative analysis,it is concluded that the most economic parameters in the selection of CFG pile composite foundation in this project are:16m of pile length,400mm of pile diameter,1600mm of pile spacing and 300mm of cushion thickness.