Research On Calculation Method Of Vertiacl Bearing Capacity And Deformation Of Pile Foundation In Granite Residual Soil

Granite residual soil is a kind of special soil.It is widely distributed in Guangdong,Fujian et.al southeast coastal areas with relatively developed economy.Most of the buildings in these areas are high-rise buildings,and the foundations are generally pile foundations,especially bored piles.Calculation of bearing capacity and settlement of the bored pile in granite residual soil will directly affect the safety,stability and economy of the building.Yet,there is no special calculation method for the bearing capacity and settlement of the bored piles in granite residual soil according to JGJ 94-2008.Based on the study of the bearing capacity and deformation calculation of the natural foundation of granite residual soil,this paper further studies the vertical bearing capacity and deformation of bored pile and the bearing capacity and deformation of rigid pile composite foundation in granite residual soil.The main work are as follows:(1)In order to study the vertical bearing capacity and settlement characteristics of bored piles in granite residual soil,we designed and constructed six full-scale bored piles.Each pile was tested by loading test and internal force test.This paper analyzed the relationship between end resistance/shaft resistance and the liquidity index(I_L)/standard penetration number(SPT-N)/effective stress.This paper also analyzed the influences of different construction method on the end resistance and shaft resistance of the bored piles in the granite residual soil,according to the measured results.(2)JGJ 94-2008 is lack of calculation method of the vertical bearing capacity of single pile of bored piles in granite residual soil.Through analyzing the engineering data,this paper proposed correction coefficient of end resistance and shaft resistance for three kind of granite residual soil,i.e.,gravelly clayey soil,sandy clayey soil and clayey soil.According to the in-situ test results of six full-scale test piles,the practicability of the proposed calculation method for the vertical bearing capacity of bored piles in granite residual soil is verified.This paper also proposed the suggested correctional method of vertical bearing capacity of single pile according to different construction method.(3)For JGJ 94-2008,there is a lack of provisions on the calculation of vertical settlement of single piles of bored piles in granite residual soil.And the settlement calculated result will have large distortion,if only calculated according to the method of ordinary clay foundation.Based on the study of the deformation modulus of granite residual soil,this paper proposed calculation method for vertical settlement of single pile based on in-situ test result.According to a large number of engineering measured data,the influences of different construction method(manual digging,drilling with casing advanced ahead,drilling with slurry)on the vertical settlement of single piles are analyzed.The correction coefficient of settlement calculation considering the influence of construction process is proposed.(4)Combining the method of bearing capacity and deformation of granite residual soil natural foundation,with the calculation method of the vertical bearing capacity and settlement of the single pile of bored pile in the granite residual soil,this paper proposed the calculation method of bearing capacity and deformation of rigid pile composite foundation considering pile-soil interaction.Based on the actual construction of the southeast coastal area,this paper conducts an in-depth and detailed analysis of the calculation method and parameter value of the bearing capacity and deformation of the bored piles in the granite residual soil,and verifies the results of this paper through practical engineering cases.The research results of this paper have important meaning for the design and construction of pile foundation in granite residual soil area.It can be used for the revision of the design rules of granite residual pile foundation and guiding the engineering practice.