Research On Soil Plug And Its Contribution To Axial Capacity Of Large-diameter Tubular Pile

Soil plug is one of the most important features of large-diameter cast-in-situ tubular pile, and has great effect on its vertical bearing capacity. Present studies on soil plug fall behind the application, and lead to unsatisfied predictions. Therefore, it is very important and urgent to do more investigation since it is the basis of pile designing.Starting from the definition, all the factors on soil plugging were studied. The paper put forward a new approach to include the influence of soil plugging in the bearing capacity calculation. The main achievements of this paper are as the following:1) After comparing all the different definitions of soil plugging, it has been found that there is a great confusion in the definition and each definition has its own emphases. Study results show that present definitions, deduced from the static equilibrium, can only be used for jacked pile of small diameters.2) The inertia force on soil plug caused by pile driving is very important for large diameter open-ended piles. The larger the diameter, the higher the plug will be, and the hight is also very related to the acceleration. Soil plugging can be more often occured in concrete pile than in steel pipe pipe.3)The research on influencing factors under static loading shows that the inside soil is not easy plugged when pile diameter increases, but will be when the wall-thickness increases. The influence of soil properties and soil distribution on plugging is much greater than pile geometires. Compared with stiff soil, soft soil is easier to get plugged. And the influence of soil distribution is greater with the penetration.4) Present domestic calculation method for open-ended pile can not predict the changes of shaft friction before and after pile penetration. It can not well estimate the increment of ending capacity either. So the prediciton is far behind satisfaction. Instead, Imperial College Pile (ICP) method can get good results.5) The paper put forward a new proproach, which the contribution of soil plug is considered. The verified results proves that this new method is beter and simpler than ICP method and can be used for this tubular pile in south-east China.