Bearing Characteristics and Mechanism of Continuous Flight Auger Pile in Weathered Granitic Soil
Weathered granitic soil is widely distributed in south China,which is fissure-rich and water-weakened.In such a special soil,bearing capacity of the commonly used slurry displacement(SD)pile is significantly lessened,while as a new technology,the continuous flight auger(CFA)pile performs superiorly,and even exceed the empirical value range for dry-drilling pile in design code.To reveal the bearing characteristics and mechanism of CFA pile in weathered granitic soil,a series of static load tests and optic fiber-based measurement on the CFA piles were performed in Huangpu District,Guangzhou.The test results show that the ultimate bearing capacity of CFA pile was twice of that of SD pile with the same dimensions,and was positively correlated to pile diameter and pile length.Size effect was not observed in the diameter range of 600 mm to 800 mm.By incorporating the ultraweak Fiber Bragg Grating sensing technique,the shaft resistance was found to follow the unimodal distribution,with the peak driven deeper from GRS to CDG by the increasing load.Ultimate shaft resistances in GRS and CDG were estimated as 128 kPa and 154 kPa,respectively,both exceeding the empirical value ranges in Guangdong/industrial pile design code.The ultimate base resistance in CDG was estimated as 3 080 kPa,double of the empirical value.Based on the soil profile excavated in the field and the CT scan image of undisturbed GRS sample,is attributed to that the associated installation method,where the pumping out of concrete and the withdraw of drill stem are executed synchronously,prohibits the development of fissure water and the resultant deterioration of the soil-pile interface.The bearing capacity of the pile type is better than that of mud pile and other dry working pile.
continuous flight auger pileweathered granitic soilultraweak FBGfissure water
万方数据
维普
