Compaction Tests as a Means of Soil Structure Evaluation

Abstract Compaction test data from the surface horizons and subsoils of 15 soils were analyzed to evaluate the most suitable data for correlations with percent carbon and percent clay. Percent pore space at maximum bulk density when correlated with either percent carbon or percent clay yielded correlation coefficients of greater statistical significance than did maximum bulk density when so correlated. This is probably because of the variations in particle (mineral) densities of the soils investigated. The particle densities will to some extent influence the maximum bulk densities attained with any compaction test, but percent pore space at maximum bulk density is not so influenced. It was concluded that unless the soils undergoing investigation have essentially the same particle densities, percent pore space at maximum bulk density is a better choice of data for correlation studies than is the maximum bulk density. Percent pore saturation at maximum density was not found to be a suitable correlation variable. A statistical highly significant correlation coefficient was obtained when optimum moisture (standard Proctor test) was correlated with plastic limit. Compaction test data from 5 montmorillonitic clay soils were compared to those from 5 kaolinitic clay soils. These comparisons failed to indicate that the montmorillonitic clay soils were more susceptible to compaction from mechanical forces than were the kaolinitic clays. Montmorillonitic clays did, however, have significantly higher liquid limits and plastic indices.