Study On The Underground Structure Anti-uplift And Uplift Pile Test

With pure basement of high-rise buildings, as well as the construction of the underground garage, plaza, make the anti-floating problem is very prominent, at present uplift piles is the main measures to adopt the anti-floating, the research of the anti-floating and uplift piles are still less, the related national standard haven’t made specific provision. So it is necessary to make the further research through model test and numerical simulation. It was mainly researched through underground structure anti-uplift, uplift pile model test, the pile-soil particle image velocimetry (PIV) test, uplift pile model of finite element simulation and engineering pile of finite element simulation. The main work and conclusions are summarized as follows:1) It was studied by model test of underground structure anti-uplift that the influence of soil permeability coefficient for buoyancy of underground structure, the influence of confined water and existence condition the basement floor in permeable and impermeable layer of underground structure influence the size of buoyancy, research shows that:when the basement floor is in low permeability coefficient of the weak permeable layer, the basement buoyancy calculation for reduction, this paper adopt the reduction factor of silt clay was 0.6.2) The properties of piles was studied by model test, it is mainly including that the differences of friction between the uplift pile and pure compressive pile, bearing capacity characteristics of uplift piles and expanded bore diameter of uplift pile, the influence of expanded bore size to enlarge bottom uplift pile bearing capacity. Research has shown that compressive pile of the pure friction pile side friction is greater than that of uplift piles, and with the increase of length to diameter ratio, the difference of both linear decrease; Expanding head improved the bearing capacity of pile obviously, but later it was limited improved for the bearing capacity by expanding bottom diameter increasing.3) The mechanical mechanism of uplift piles was studied by using particle image velocimetry (PIV) technology, because of the axisymmetric model of pile and soil features, enlarge bottom uplift pile transparent model was established, a series of image data was collected in the process of uplift pile moving up, the displacement of pile and soil was analyzed by image analysis program in MATLAB. Research has shown that the procedure of pile moving up was divided into four stages, including strengthening of soil stage, the pile side friction works stage, the diffusion Angle of expanding stage, the formation of critical slip surface stage, and explained the reason of bearing capacity increased in the expansion of bottom uplift pile.4) The uplift model pile was simulated through finite element analysis software ABAQUS, the simulation results was analyzed between the model test and the PIV test, the results affirmed the reliability of the analysis of ABAQUS, at the same time, the simulation results acquired some physical quantities that not easy to measure in the model test, such as axial force of pile, pile side friction and displacement vector and displacement contours, stress contours etc. and it is helpful to analyze characteristics of vertical bearing capacity of the piles.5) The above research results was promoted to the engineering pile application, by the numerical simulation analysis, it was studied that the characteristics of vertical bearing capacity of the engineering pile through finite element analysis with equal proportion engineering pile, the influence of different factors on the bearing capacity was studied at the same time. Research has shown that:it is not economic by increasing the pile diameter to improve the bearing capacity, but the increase of the expand head to improve the bearing capacity have a significant effect; ultimate bearing capacity of uplift pile is not only depends on the size of the pile diameter d, but by pile diameter d, expanded bore diameter D and the angle of expansion bottom 8, so it is important to choose rational angle 8 in the design of the expand head uplift pile.