Studies On Bearing And Deformation Mechanism And Shaft Resistance Degradation Of Super-long Piles Under Vertical Loading

With the development of super-tall buildings and long-span bridges,it is necessary to massly use super-long piles because of their high bearing capacity. Although a great number of super-long piles have been used,the research on theory of super-long piles is far behind the development of practice. So,it is not only the demand of development of pile theory,but also the need of engineering practice.This thesis discusses the pile calculate theory and the research actuality of super-long piles firstly and gives a compositive commentary. Then,by using the great FEM programme and the Drucker-Prager Model,the thesis establishes the pile-soil model of super-long piles,analyzes the mechanism of bearing and deformation of super-long piles under vertical loading systemically,studies the characteristics of Q-S curve,bottom resistance,pile shaft resistance and critical length of super-long piles in detail,acquires some practical guidance conclusion.Secondly,with a practical engineering,the author expatiates the bearing characters of super-long piles farther. The thesis points that super-long piles are frictional piles under the condition of working loading. So we should ascertain the bearing capacity through the settlement. Super-long piles are compressive and the compressibility should be considered in the calculation of settlement. The bottom resistance and the shaft resistance exert asynchronously,so it is necessary to adopt different coefficient. The thesis also points that it is important to adopt pile end(side) grouting and tapered piles.Aimed at the phenomena of shaft resistance degradation of the super-long piles during the course of loading,the author gives an elementary theoretical discusses. It analyses the influence of ,dilatancy,rotation of soil cell's principal stress,pore water pressure and the damage softening. The author puts forward a critical value of 0.01D-0.02D to judge the pile-soil slippage. The thesis also discusses the residual strength after slippage. Based on this,the author establishes the analytics of load-settlement of super-long piles in homogeneous soil with the account of shaft resistance degradation and extends to layered soils.