Influence Of Press-in Piling On Soil Mechanism Based On Multi-Scale Test

In recent years, the press-in pile has been widely used because of the advantages of no noise, no vibration, low construction stress and high quality. On the one hand, press-in pile belongs to the displacement pile. The process of pressing in pile will make the surrounding soil compacted. It will result in larger increment of lateral earth pressure, which might cause adversely affect to the surrounding environment or adjacent buildings. Therefore, it has great significance to have a comprehensive understanding of the compacting effect to carry out the research about the increment of lateral earth pressure around the pile in practical engineering. On the other hand, the interface of soil and pile will have a large deformation in the process of penetration on account of the interaction between pile and soil, which involve the strain localization, discontinuity, large deformation. It is crucial to correctly analysis the deformation mechanism, shear failure, the process of load transferring and to correctly simulate the process.In this paper, the macro mechanical behavior and the micro behavior of sand in the process of pile penetration are studied by the model test of the press-in pile. By means of monitoring the lateral earth pressure in the process of pressing, the development of lateral earth pressure, effect on the sandy soil during the process of penetration, the influences of different type of pile on sandy soil could be analysised and discussed. The main conclusions are as follows: the effect of pile penetration on the lateral soil was greater than the soil under the bottom of pile, it presents the form of elliptical model. With the increase of pile penetration depth, effects on the soil gradually increased; the peak lateral earth pressure increment along the horizontal direction fits power function. The influence range size is from about 11 D to 22D(D is the length of pile cross section), and the influence range size present a linear growth with depth of soil; the peak lateral earth pressure increment along the depth of soil fits the linear function, but the growth rates are different in each position; the increment of lateral pressure of the corresponding point has reached the peak before the pile reached the depth of measuring point, namely there exist a phenomenon of advance. While this phenomenon is not obvious for the far measuring point; the influence on the sandy soil of square pile and round pile in the process of penetration were compared. The research shows that the influence on the soil of round pile and square pile are roughly the same in the process of pressing. To the influence range size on soil under the pile tip, square pile is greater than round pile, while round pile is greater than square pile on the horizontal direction;the selection of pile type and the form of the pile have a great influence on distribution rule of growth rate of the lateral earth pressure increment peak value along the depth.Meanwhile, the movement of soil particles between soil and pile were recorded. The displacement of contact particles between soil and pile were calculated by using the digital image technology(DIC), and the displacements of the contact particles are preliminary analyzed. Conclusions are as follows: the vertical displacement of the contact particles is the much great than the horizon displacement, which presents the localization feature. But the regularity is not obvious; the influence of velocity on particle displacement is mainly reflected in the stage of the initial movement from the static condition in the same penetration depth; the final value of the cumulative vertical displacement is larger along with the increase of depth of penetration in the same pile pressing rate.