Analysis Of Pile-Soil Interaciton Charcteristics And Effective Length Of Pile Of Composite Foundation Based On Fem

Composite foundation, for its good applicability and economy, has been widely used in subgrade of high-speed railway and highway. With the rapid development of high-speed railway and highway, design standards has been greatly improved. So it is very common that High-strength pile was used for foundation reinforcement treatment in high-speed rail and road subgrade. However, due to the theoretical study of the bearing mechanism of high-strength friction pile obviously lagging behind in engineering practice, increasing the length of the pile blindly in the engineering design in order to improve the reliability of engineering, resulting in not only improving the construction costs, but also bringing difficulties to the construction. Against this widespread phenomenon, the contact problem of structures with soil was investigated firstly by ADINA, the widely used general-purpose finite element software. Based on this, the finite element model of soil interaction of a single pile was established. The influencing factors of effective length of high-strength friction piles and the impact of the law on the effective length of pile were analyzed, our main work is as follows:(1) The constraint equations method was improved as dealing with friction element contact problem in ADINA, obtained tangential contact conditions similar to the Goodman unit, realized the extreme conditions of tangential contact in control of the critical relative displacement increment(the Sliding state).In analysis of the contact characteristics between the structure and soil structure, this outcome was of great significance for simulating the critical displacement of soil body when sliding-shearing. The numerical calculation of the slider model was carried out based on the conclusions through ADINA, the impact of the law of the conditions and parameters of contact calculation on the results was analyzed. Calculations show that: Friction and normal force is proportional to the coefficient of friction; The greater the critical relative displacement increment, the larger relative displacement of the slider sliding correspondingly, the smaller tangential friction of contact surface at the same displacement before sliding through calculate.(2) The conclusions that the simulation of that contact characteristics between the structure and soil based on ADINA, analysis model of pile soil interaction when top load on a single pile imposed was established, and has been verified by a geotechnical centrifuge model test. With the established finite element model of soil interaction of single-pile, the characteristics of load transform of flexible single pile and high-intensity single pile was analyzed. The characteristics of load transform in flexible single pile and high-intensity single pile with a bearing load of different length and a pile length of different bearing load were discussed. Based on it, the characteristics of interaction and load transform of flexible single pile and high-intensity single pile was analyzed. Analysis showed that:load transform capability of High strength friction pile was significantly better than flexible piles, the diversification of Pile length and load will cause body axial force of high-strength friction pile redistribution within the length of the pile, but have little affection on tip resistance and the settlement of pile top.(3) Combination of characteristics of pile-soil interaction between flexible piles and high strength piles, the concept of critical length and the effective length were distinguished, pointed out the core of both was the play of pile shaft resistance, and built a method of determining the effective length of the pile based on the play of pile shaft resistance. The affection on the effective length caused by factors such as the pile bearing load, modulus of soil between piles and the friction coefficient of pile-soil interface. The results show that, the effective length of the high-strength pile increases with the increasing of the pile bearing load, decreases with the increasing of the modulus of soil between piles and the friction coefficient of pile-soil interface.