Abstract: The grain-size analysis of expansive soil, loess and laterite is carried out by laser particle size analyzer. The influence of sample mass and ultrasonic dispersion time on the test results are studied. It is found that there is a good linear positive correlation between the shading rate and the sample mass. The suitable shading rate range (15%~25%), sample mass (0.1~0.2g for expansive soil, 0.4~0.8g for loess, 0.2~0.4g for laterite) and ultrasonic dispersion time (6min for expansive soil, 2min for loess and laterite) in tests of laser particle size analyzer for special soils are given. The test results dispersion of laser particle size analyzer is small for loess and expansive soil, but is relatively large for laterite. In parallel tests, the maximal range of fraction content for laterite is 10.1%. Compared with the hydrometer method, the content of colloidal particles (smaller than 0.002mm) measured by laser particle size analyzer is smaller, while the content of clay particles (0.005~0.002mm) or larger particle fraction is larger, which may be caused by the different test principles of these two methods. There is a relatively large difference between these two methods in test results of laterite, which may be related to its special properties. The research results provide a reference for the application of laser particle size analyzer in the grain-size analysis of special soils.

Key words: laser particle size analyzer, special soil, grain-size analysis, hydrometer method, shading rate