Measurement Of Soil Specimen Surface Deformation Field In Tri-axial Test

Tri-axial test plays an important role in soil mechanics and engineering application. Measurement of specimen deformation is an important step in tri-axial test, whose result directly affects the mechanical properties of soil. Study on surface deformation of tri-axial specimen is to obtain more accurate deformation information for the mechanical properties research of soil. This paper analysis the surface deformation of tri-axial specimen based on digital image measurement system based on sub-pixel accurate corner recognition.This paper analysis the resources of measurement error and focus on camera distortion and error from dial length replaced by chord length. The results show: (a) camera distortion can be ignored, (b) in the dial length and dial deformation measurement, edge recognition is more reliable than corner point recognition, so the paper suggests introducing the edge recognition technology in the corner point recognition's measurement system.It also analysis the cylindrical sample imaging characteristics and gives the idea to solve the surface deformation field that is: first, it introduces a pixel equivalent to the processing, then calculates circle deformation or horizontal deformation, and analysis the relationship of circle deformation or horizontal deformation and dial deformation, thus calculate dial deformation.The paper discusses the two basic assumptions' rationalities and the function in the dial deformation processing. It calculates the dial deformation by iterative, but the result is not enough stability. It needs further discussion.Because the arc length of specimen does not change with the cameral location, the paper successfully make mosaic of two images independent photographed by two cameras. It achieves the full surface deformation field of specimen.In this paper, the axial strain field, through the analysis of the calculation process and examples of applications that is stable and reliable.