Analysis And Research On Horizontal Static Load Tests On Single Large Diameter Under-reamed Pile

Large diameter belled pile has been widely used in Multi-storey and high-rise buildings, bridges, factories and other large equipment and heavy engineering for its simple construction, reliable and easy to check, large capacity, no noise interference and the advantages of significant economic benefits. In this paper, the level of load on the large diameter hand-dug hole pedestal pile deformation mechanism and the load bearing characteristics of the work are studied in details based on the static load test, numerical simulation and theoretical analysis.(1) After the static load test scheme is studied from the loading level, deformation, test devices planted, set of working point, time of data readings and loading-unloading method, a feasible plan is achieved for horizontal load field test of the large diameter hand-dug hole pedestal pile. On-site static loading test for the four root level load enlarged end of large diameter pile is carried out to determine its critical load, limit load bearing capacity, horizontal bearing capacity eigenvalues and corresponding displacement. Meanwhile, the internal force test of pile body is carried on for getting the test data and experimental results to further research the horizontal load transfer mechanism of shear stress and bending moment and pile body along the depth change rules.The results are included in the below:a) the H-Yo curve and H-?Y/?H curve of large diameter pile can be divided into three stages, namely elastic stage, elastic-plastic stage and destroy stage; b)there exsits the obvious nonlinear relationship, which can be approximated to fit a hyperbolic line, between the horizontal resistance coefficient of the foundation soil proportion coefficient and the displacement of pile top.; c)at the largest cross-section bending moment, the reinforced stress linearly increases with the load increasing. When the horizontal load reaches limit, strain value mutations that pile body fractures. This shows that the limit of the horizontal load is controlled by the strength of the pile; d)Bending moment distribution is evenly larger from top to bottom when it is getting a depth of 3-4D maximum, and then smaller. A moment in the cross-section place of pile is still produced, especially in the shorter S22 pile. This shows that the belled has great influence on the distribution of bending moment.(2)Through FLAC3D program and Mohr-Coulomb criterion, a numerical simulation calculation for the large diameter belled pile under horizontal loads is carried out to analyze the displacement rules of pile body along the buried depth of pile body regularity of distribution and the influence of the surface soil modulus of elasticity and enlarged end of pile body size on the displacement of pile body. It can be showed that the result has a good consistency with the test results, and that the upper layers of elastic modulus has notable influence on to the influence of pile body horizontal displacement of the pile body. In order to ensure a good level of pile bearing capacity, the topsoil elastic modulus is above in appropriately lOMPa. To fully play to the horizontal bearing capacity of large diameter belled pile, Pile length should be around for the 7D, but should not be greater than 10D.(3)The horizontal bearing capacity calculation method of large diameter belled pile based on the foundation counterforce and pile body strength is proposed to analyze the impact of the pile body size (pile diameter, belled diameter, the pile length and the height of pedestal), soil around the pile and properties of pile tip soil on the horizontal bearing capacity of pile. The calculations show that the large diameter belled pile is rigid pile. Based on different critical conditions, the three horizontal bearing capacity calculation formula of large diameter belled pile,, clear concept and clear meaning, is derived according to force balance, moment balance and strength of pile, by which the horizontal bearing capacity of large diameter belled pile can be easily computed. Through the comparison with standardized method and measured value of engineering, it shows that the results from the calculation formula of pile body strength for the level of the bearing capacity are nearly identical to the on-site measured results.The results of this paper provide a theoretical basis for design and construction of large diameter belled pile, and also have the positive significance for theorectical research.