Abstract: The influence of different concentration of sodium hexametaphosphate solutions on the laboratory grain size distribution analysis results (densitometer method) on the soft clay samples from a ground improvement project in estuary area of Bohai. The test results indicate that, the concentration of sodium hexametaphosphate solutions have a significant impact of the test results. The sodium hexametaphosphate solution should be used in the laboratory gain size distribution test. For the soft clay sample from estuary area of Bohai, the dispersion solution should use 10 ml sodium hexametaphosphate solution with a concentration between 6% and 8%. With the appropriate concentration, the test results demonstrate a good stability. The content of finegrained group increased with the increase of sodium hexametaphosphate concentration and tended to be stable. The content of powder first decreased and then increased, and the content of clay first increased and then decreased.

Key words: grain size distribution analysis, densitometer method, sodium hexametaphosphate, peaty soft clay