Development Of Stereo Particle Image Veiocimetry For Investigation Pile-soil Interaction

With Chinese large-scale construction development, there are a large number of high-rise buildings, bridges and ports., Chinese and foreign scholars has paid more and more attention to pile foundation which are under wind load, tidal load, seismic load, and other lateral load. It is important for the research of pile-soil interaction effect to correctly analyze the stress and deformation of soil mass around pile foundation. Particle image velocimetry (PIV) was used in this research to measure the displacement field of soil particles. The PIV technique is an undisturbing, full field, and dynamic measurement technique.With the PIV technique development, the stereo particle image velocimetry (Stereo-PIV) has gradually applied in some disciplines in laboratory study. This experimental equipments were designed by the author. The developed Stereo-PIV program was made by author, that based on MATLAB camera calibration toolbox and PIVview2C software, which are free obtained from internet. The three dimensional displacement fields of soil surface were measured by the Stereo-PIV program. The concrete work and the main conclusions are as follows:(1) Present understanding of pile-soil interaction is not efficient enough to capture the deformation mechanism when pile under laterally loaded because of the complicated behaviour. A new measurement method, Particle Image Velocimetry (PIV) is used to measure the soil deformation around a laterally loaded pile. The principle of the PIV technique was presented and then laterally loaded pile research at home and abroad was reviewed. The study was focused on the PIV technique to measure the soil displacement and analyze pile-soil interaction.(2) In order to meet the special requirement of laterally loaded pile tests, that need to capture the displacement, force, and images simultaneously, a data acquisition system was developed based on LabVIEW software. The physical displacement and force can be converted to the data stored in computer. Using the time mark, the displacement, force and image data were obtained at the same time.(3) The PIVview2C software was introduced, that was based on the PIV principle. This software can choose window size, correlation method, vector plotting parameters, and so on, which is excellent software to measure two dimensional displacements.(4) Setting one CMOS camera parallel the soil surface, a series of images of soil movement was captured by the camera. The pictures before and after move were analyzed using PIVview2C. The pile-soil interaction was analyzed, including the pile displacement and lateral load, the soil two dimensional displacement, the shear strain field, and the difference of soil movement at different lateral load.(5) Setting two CMOS cameras separately parallel the soil surface and the soil profile, the planar displacement and vertical displacement were simultaneously captured. Under confined condition, the pile-soil interaction was analyzed.(6) The relationship of image coordinate system, camera coordinate system, and world coordinate system was studied. The recomposed MATLAB camera calibration toolbox can obtain intrinsic and extrinsic parameters of both right and left cameras. The Stereo-PIV program was made by author, based on the MATLAB camera calibration toolbox, PIVview2C software, and three dimensional collinearity equations. This developed program can be easily adjusted to meet user needs at a much lower cost, as compared with commercially available systems. Another reason is this method is easy to realize relative to other Stereo-PIV method.(7) Setting two CMOS cameras at different place and angle, the paired images of soil surface movement were simultaneously captured. At different lateral load the pile-soil interaction was analyzed, which mainly included the pile displacement and lateral load, the soil horizontal and vertical displacement fields, soil particles movement angle, the shear strain field, and the difference of soil movement at different lateral load. The influence area of the soil surface by the circular pile was predicted. The prediction was also verified by comparison with field test data.