Study On The Design And Calculation Theory Of Composite Foundation With Large-Diameter Plain Concrete Piles

Plain concrete pile composite foundation has the advantages of advanced technology. high construction speed, short construction period, low engineering cost and so on, so the plain concrete pile composite foundation has been more and more widely used in engineering.In recent years, there have emerged another kind of concrete pile composite foundation--large diameter concrete pile composite foundation. According to the geological conditions of Chengdu area, reconnaissance and Design Institute of China Southwest Architectural put forward this concept, and this kind of composite foundation has been used in many engineering subjects such as green land in Chengdu, Bai Shi Mansion, new hope Phnom No.1. Longhu Century City, the peninsula engineering.The pile diameter of plain concrete pile and composite foundation ranges from400to600mm,while the pile diameter of large diameter concrete ranges from800to1200mm. Because of the large size of pile diameter, the contact area between pile and soil is bigger, which makes a better use of the soil between piles.and which can improve the bearing capacity of the foundation and reduce the foundation settlement. At present it is designed by the control of bearing capacity towards large diameter concrete pile composite foundation.but high-rise buildings are often based on settlement control.Therefore, the current design method has obvious defects that it can not reflect the deformation characteristics of this kind of composite foundation.In this thesis, on the basis of previous work, combined with the field monitoring data and Theoretical derivation, by studying the large diameter concrete pile composite foundation deformation characteristics, I proposes a theory and a design method which can reflect the force deformation.This dissertation is about the following several aspects:(1)By analyzing the results of field monitoring. it concludes the regular pattern of the axial stress of pile.pile-soil stress, and pile-soil stress ratio variation.(2)Through the derivation of deformation theory based on coordinated deformation theory of pile and soil.and combined with the field monitoring results,and by studying on deformation characteristics of large diameter concrete pile composite foundation deformation characteristics.it figures out the form of pile side friction spreading along the pileAccording to the form of pile side friction spreading along the pile,it is simplified as linear distribution.The maximum negative skin friction is on the top of pile,and the maximum positive friction is on the bottom of the pile,which we can validate by the site monitoring.(3)Based on the simplified model of side friction of pile, the dissertation put forward the simplified calculation theory and its design method of large diameter concrete pile composite foundation based on coordinated deformation theory of pile and soil.And through three engineering examples it verifies the application of this method.