Study On The Effect Of Integrity Of Bored Pile On Bearing Capacity Of Pile Foundation

Foundation engineering is the important constituent of the architectural engineering. In the ground foundation engineering, the quality of pile foundation is directly relative to the structure security of the entire building. The quality detection of foundation piles including two important contents: bearing capacity detection and integrity detection. The two Influence factors of pile bearing capacity are the pile structural strength and the foundation soil intensity. Usually, people always discuss the influence of bearing capacity on the second factor, and the first factor is neglected. So the conclusion from the quality detection will be not comprehensive. In this research, according to the pile integrity detection, defect locations and types are determined. And considering the stratum condition, the deformation of pile can be obtained. Then the bearing capacity of pile is estimated by finite element method. After that, the influence of bearing capacity on different defects of pile foundation is analyzed. Finally, according to the integrity detection, using the project analogy method, the other project piles bearing capacities in the identical location are estimated. This combination method of integrity detection and the bearing capacity detection can greatly reduce the detection quantity of piles. So the application prospect of this method is very good.In the research, based on the daters of integrity detection, the finite element model of bored pile is established. And then the influence of defects on pile bearing capacity is analyzed. In the practice project, detection tubes were buried in advance which is used to detect the concrete of pile body top-down comprehensively. According to the acoustics parameters (sound reach time, wave amplitude, frequency and so on) and profile ofultrasonic which transmits in the concrete, the concrete quality is analyzed. And the pile break, hypoperfusion on the top of pile and dregginess in the bottom of pile are discovered. Through many experimental study and project detection, ultrasonic wave detection is a sensitive, accurate and reliable method. It can comprehensively provide the concrete integrity of pile body and the estimate concrete intensity. So far it is the most accurate method to estimate concrete flaw of pile body.In the article, the self-balanced static load tests were carried on three piles of one bridge engineering in a road of Jilin province. The bearing capacity of pile is analyzed by numerical modeling, and the P-S curve obtained by numerical modeling and measured curve by the static load tests is anastomotic. The finite element method is based on the continuous medium supposition that means there is no pore between elements and nodes. But soil mass is not continuum, it is plastoelastic mass. So there must be errors to the results by finite element. But from the results, analyzing the bearing capacity of pile by finite element method is still effective.The influence of bearing capacity on different defects of pile foundation is analyzed by finite element. And in the research, the rock and soil mass around pile foundation is considered respectively to be clay, argillaceous shale and sandrock.When dregginess is at the bottom of pile, the bearing capacity of pile was analyzed by the numerical simulation. And the research indicated that when dregginess thickness H increased from 0 to 100 millimeters, bearing capacity of pile is losing in a big way along with the dregginess thickness increase, when H is smaller than 300mm, the single pile bearing capacity changes remarkably, but when H is bigger than 500mm, the influence of changes of dregginessthickness was not very obviously on the single pile bearing capacity. When H increased from 0 to 100mm, in the clay mass, the single pile bearing capacity reduces 22.1%; in the argillaceous shale, the single pile bearing capacity reduces 8.6%; in the sandstone, the single pile bearing capacity reduces 6.9%.Then, the analysis of the influence of broken pile to the bearing capacity is discussed. The position of broken pile is assumed to be at 35-37m, 18-20m, and7-9m. Then rule of bearing capacity is analyzed. The analysis indicated that in process of load transmission along pile body, the pile body transmits the load to the soil mass around pile when there is break,The biggest principal stress increased and the deflection happened, the biggest principal stress of the pile body below the broken pile position reduced obviously. The displacement only on the top of flaw the pile body occurred obviously under the load function, the pile bearing capacity can not display sufficiently. If it is in the clay and the flaw thickness is 500mm, the position of the flaw is at the range of 35 to 37m of the pile body, the bearing capacity of single pile is 65.6% of complete pile; when it is at the range of 18 to20m, the bearing capacity of single pile is 59% of complete pile; when it is at the range of 7 to 9m, the bearing capacity of single pile is 41% of complete pile. And if it is in argillaceous shale and the flaw thickness is 500mm, the position of the flaw is at the range of 35 to 37m of the pile body, the bearing capacity of single pile is 81.4% of complete pile. When it is at the range of 18 to20m, the bearing capacity of single pile is 62.5% of complete pile. When it is at the range of 7 to 9m, the bearing capacity of single pile is 50.3% of complete pile. If it is in the sandstone and the flaw thickness is 500mm, the position of the flaw is at the range of 35 to 37m of the pile body, the bearing capacity ofsingle pile is 82.7% of complete pile. When it is at the range of 18 to20m, the bearing capacity of single pile is 73.4% of complete pile. When it is at the range of 7 to 9m, the bearing capacity of single pile is 41.3% of complete pile.The influence of hypoperfusion on the top of pile to the bearing capacity is analyzed. And the analysis indicated that in process of load transmission along pile body, the displacement of pile body blow the defection is smaller, but on the top of the pile where is the flaw position, the displacement occurred obviously. And the displacement depends on the physical and mechanical characteristics of the flaw. When soil mass around pile is clay, the bearing capacity of single pile is 39.3% of complete pile. When soil mass around pile is argillaceous shale, the bearing capacity of single pile is 19.6% of complete pile. When soil mass around pile is sandstone, the bearing capacity of single pile is 19.6% of complete pile.The bearing capacity of single pile increases along with the increases of the flaw position in the pile body growth. And it is connect with the elastic modular ratio of pile body and the soil mass around the pile. The bearing capacity of single pile increases as logarithmic function form. The function equation is: Qu=Aln(h)+B, Qu - limit bearing capacity of single pile, h - the depth of flaw position, A– parameter which has connection with elastic modular ratio of pile body and the soil mass around the pile, B - parameter which has connection with shearing strength.