INVESTIGATION OF LASER DIFFRACTION and SEDIMENTATION METHODS WHICH ARE USED FOR THE DETERMINATION OF GRAIN SIZE DISTRIBUTION OF FINE GRAINED SOILS

Abstract

ABSTRACT Grain size distribution determination for soils is very important in soil mechanics discipline. In order to predict the soil behaviour it is necessary to know grain size distribution. Soils can be broadly classified as coarse and fine-grained. Grain size distribution of coarse-grained soils like sand and gravel are determined by sieving. However sieving cannot be used for clay and silt sized particles, for these soils sedimentation techniques based on Stokes Law are   used.   Sedimentation techniques, which can be classified as pipette and hydrometer methods, utilize setting velocities of grains in water, to determine grain size. Stokes law involves a number of simplifying assumptions and these assumptions cause some mistakes in grain size determination. In this study principles and details of the sedimentation technique and the laser diffraction technique, which is a rather new technique, were given and measurement mistakes due to the assumption of Stokes Law were briefly discussed.   Key Words: Grain Size Distribution, Sedimentation, Laser Diffraction Method