The Error Correction And Data Processing Of Digital Image Measurement Based On Plane Strain Experiment

Plane strain experiment belongs to a special kind of triaxial test which imitates the transformation of the soil in the state of plane strain stress in engineering practice. It is applied to study the shear properties of the soil in plane strain state. There are quantities of plane strain issues in practice geotechnical problems, such as earth and rockfill dam, retaining wall, embankment, strip foundation, etc. In view of the particularity of the plane strain problems, it is very necessary to research and develop the plane strain apparatus that can simplify the complexity of the problem as well as improve the measurement accuracy.There are a number of advantages of the new plane strain apparatus combined with digital image measurement system based on corner recognition, some of which are contactless measurement, high measurement accuracy, possibility of recording the whole procedure of specimen deformation with pictures, convenience to observe the state of the specimen at any moment after experiment.This paper analyses the source of error in digital image measurement system and focuses on the influence brought by camera lens distortion. Then various methods to calibrate the camera model are discussed. The paper also introduces two different kinds of methods to calibrate and revise the lens distortion in details. The experiment results prove that the calibration outcome is accurate and effective according to the theoretical model.With the data obtained by the image measurement system, the paper calculates the horizontal and vertical deformation utilizing four-node isoparametric element in finite element. After calculation it draws the deformation field in the form of contour map. As a result, the researchers are able to observe the trend of specimen deformation directly. The method offers basis for the research of shear band.