Global Stability Analysis Of CFG Pile Composite Foundation Under Embankment Based On Muitiple Failure Mechanism

With the gradual implementation of the National Comprehensive Transport System Plan,the construction of transport infrastructure has been developing vigorously,especially with the rapid development of high-speed railways and expressways,especially with the increase of design speed,the requirements of subgrade structure and foundation stability are more and more strict.Traditional Foundation treatment methods can not meet the requirements of postconstruction settlement of embankment and foundation stability,rigid pile composite foundation is widely used in engineering because of its good settlement control ability and different treatment methods can be chosen according to different site environment and construction conditions.However,even if the rigid pile composite foundation,the overall instability of the foundation engineering accidents also occur from time to time.In view of the checking calculation of the stability of the Composite Foundation with rigid piles under the embankment,the analytical method is not clearly given in the code,and the related research results only propose the checking calculation method for the single failure mode,which lacks consideration for the actual failure mode of the foundation,there is no unified method for stability analysis of rigid pile composite foundation.Therefore,taking the CFG pile as the research object,the whole stability analysis of the CFG pile composite foundation under the embankment based on various failure modes is carried out:(1)The pile-soil interaction and stress analysis under six failure modes of CFG pile composite foundation including sliding failure,overturning failure,bending-tension failure,bending-compression failure,shearing failure and flow-around failure are discussed,a set of stability analysis method of CFG pile composite foundation under embankment is established,which considers the pile-soil mechanical failure characteristics under different failure modes.The study shows that different failure modes of CFG pile present different failure characteristics of pile and soil,and for the main failure mode of CFG pile ——Bending failure,the non-uniform failure characteristics are characterized by introducing the Coefficient of flexural capacity of pile body at different section positions.(2)Based on the analysis of eight main factors affecting the stability of CFG pile composite foundation,the contribution of pile,soil and reinforcement belt to the anti-sliding of CFG pile composite foundation is discussed.The results show that there is a negative correlation between embankment height,pile spacing and CFG pile composite foundation stability Factor of safety;The cohesive force of the soil,the angle of internal friction of the soil,the tensile strength of the cushion reinforcement,the length of the pile cap,the diameter of the pile and the strength grade of the pile material are positively related to the Factor of safety of the CFG pile composite foundation For CFG pile composite foundation,the average contribution is 63%,the average contribution is 31%,and the average contribution is6%.(3)The influence of various factors on the stability of CFG pile composite foundation is analyzed by range analysis and variance analysis with orthogonal table,and the influence of these factors on the Factor of safety of CFG pile composite foundation is obtained,the multiple linear regression is used to get the regression equation which can predict the stability of CFG pile composite foundation Factor of safety.The results show that the influence of various factors on the stability of CFG pile composite foundation is as follows:embankment height > internal friction angle of foundation soil > cohesion factor of foundation soil > pile spacing > width of pile cap > material strength of pile body > ultimate tensile strength of cushion reinforcement material > pile diameter.The height of the embankment,the angle of internal friction and the cohesion of the soil have a significant influence on the stability of the CFG pile composite foundation,the distance between piles and the width of the pile cap have a significant influence on the stability of the CFG pile composite foundation,other factors are not significant.The relative error between the prediction result and the calculated value of the regression equation is within ± 10%,which has a good prediction effect and can provide some guidance for the design work.