Abstract: Sand particle grading is one of the important parameters affecting the engineering properties of sand. The traditional grain
size analysis methods have different application range due to different test principles. In order to obtain sand particle gradation more
conveniently and accurately, a new method based on digital image processing technology to obtain sand particle size parameters and
grading characteristics in SEM photographs is proposed. The prepared sand samples are polished into thin slices and photographed
under a scanning electron microscope. Then the photos are stitched by Photoshop software, and the self-developed SMAS digital image
analysis system is used to quantitatively analyze the stitched photo to obtain the stuctural parameters of microscopic samples. The
obtained“equivalent diameter of soil particles”and“area of soil particles”are respectively equivalent to the actual soil particle size
and soil particle quality, which can be converted to the particle gradation curve of sand. The obtained sand particle gradation curve is
compared with the particle grading curve obtained by the traditional sieving method and laser particle size analysis method. The
validity and reliability of the proposed digital image processing method are verified. The differences between digital image processing
methods and traditional grain size analysis methods are analyzed, and their advantages as well as disadvantages are discussed.

Key words: sand, particle gradation, digital image technology, grain size analysis method