Study On Mechanism Of CFG Pile Composite Foundation In Collapsible Loess Area

The CFG pile composite foundation has the engineering characteristics of improving foundation bearing capacity and reducing foundation deformation,and is widely used in high-rise and super high-rise buildings in the loess area.The parameters in the design of most CFG pile composite foundations are based on experience and lack scientific basis.Therefore,it is of great significance to study the factors affecting the bearing capacity and settlemeof CFG pile composite foundation in collapsible loess area.Based on the engineering background of a high-rise building in Xianyang City,this paper studies the bearing capacity characteristic value and settlement of CFG pile composite foundation based on current norms and field tests,and uses MIDAS/GTS finite element software to establish engineering calculation model.The influence of factors such as cushion modulus,thickness,internal friction angle and replacement rate on the pile-soil stress ratio and settlement value.The main research results are as follows:?1?The reinforcement mechanism of the composite foundation,the action mechanism of the cushion and the calculation formula of the bearing capacity and settlement are summarized,which is the theoretical basis for the actual engineering calculation.The meaning and value of each coefficient in the calculation formula are systematically explained.?2?Based on the engineering background of a residential building in Xianyang City,the experimental principles and methods of geotechnical test,static load test and low strain dynamic test are expounded.After sorting and arranging the test data,the test results show that the engineering scheme meets the specifications and design requirements.?3?Combining the measured data of the project and calculating the bearing capacity and settlement of the composite foundation according to the theoretical norms,and analyzing the results,the contribution value of the pile body is conservative in the design of the foundation treatment,that is,the value of ?₁ and ? is biased.The calculation of the bearing capacity of the foundation is greater than the test value..Furthermore,the calculation formula of ? is derived according to the bearing capacity formula,and the values of ? in different cases are explained.?4?Using MIDAS/GTS finite element software to establish the three-dimensional model to the stress and displacement cloud map of pile and soil,and compare the bearing capacity value obtained by data simulation analysis with the theoretical calculation value and test value to confirm the numerical simulation of CFG pile.Feasibility of composite foundation bearing capacity.The numerical analysis of the influencing factors of the stability of composite foundation shows that the modulus of the gravel cushion is 20-100MPa,the thickness is200-300mm,the internal friction angle is 40-45°,and the composite ground replacement ratio is0.06-0.08.