Introduction of a new method for determining the particle-size distribution of fine-grained soils

Particle size distribution is determined by various methods such as laser diffraction scattering, image counting, sieving and sedimentation methods, none of which are perfect and need to be refined in the fields of soil science and civil engineering. This study tried to achieve a more accurate method for gradation of fine-grained soils. Regarding the concept of sedimentation and spectrophotometry, experimental and theoretical studies have been done on the particle size measurement of seventeen fine-grained soil samples. The diameter of the particles was determined on the basis of the Stokes' law of settling velocity for particles in suspension placed in the cuvette whereas the percentage finer than these diameters were determined by a formula derived herein using the spectrophotometry method at the operating range of 900-1000 nm. The ratios between the concentration values at each reading time and the initial value were related to the percentage of particles passing. The gradation curves obtained by this method for the soil samples in this study correspond to the curves of microscopy imaging analysis. Compared with other methods, this test procedure and the related calculations are rather convenient.