Sediment grain size analysis (Granulometry)

Sediment grain size analysis (granulometry)

Source: HIMOM

Introduction

The objective of grain size analysis is to determine the grain size characters of sediment samples and subsequently classify samples based upon their constituent parts. Particle size analysis is performed using laser diffraction techniques (<2mm fraction) and sieving techniques (>2mm fraction). Sediments containing a mixture of both fractions are analysed by both methods and the results integrated. The results from the particle size analysis are used to generate size distribution plots, to calculate statistical operators including mean and sorting, and to obtain %clay, %silt, %mud, %sand and %gravel in order to classify samples into sediment types.

The laser diffraction technique is described in the HIMOM manual. The sieving technique is executed as follows:

1. Put the sediment sample in an oven at 60-80.C to calculate total dry weight (it’s advisable to take a sample of ca. 100g dry weight).

2. Remove the fraction <63um, by sieving the sample through a 63 um sieve under a water flow.

3. Dry the remaining fraction in an oven at 60-80.C

4. Put this fraction in the analytical sieve shakers to separate the different fractions (>1000um; 1000-500; 500-250; 250-125; 125-63um).

5. Weigh the residuals in each sieve, and express as a percentage of total weight, including the weight of the fraction <63um, which is calculated by subtraction.