MODELLING SOIL STRENGTH CHARACTERISTICS BASED ON INDEX PROPERTIES AND LEVEL OF COMPACTION

This paper presents data on soil compaction, generated as part of the Indian Pavement Performance Study, and correlations derived from it between maximum densities, optimal moisture contents and strengths for two compaction levels: (1) standard Proctor compaction; (2) modified AASHTO compaction. The laboratory study on comparative compaction and strength characteristics of subgrade soil subjected many soil samples to the following tests: (1) mechanical analysis; (2) Atterberg limits; (3) Proctor density and optimal moisture content (OMC); (4) modified AASHTO density and OMC; (5) California Bearing Ratio (CBR) at 100% Proctor density after 4 days soaking; (6) CBR at 100% modified AASHTO density after 4 days soaking. The paper presents the data in tables and charts, and applies various multiple regression analyses. The following results were obtained: (1) the strength of the subgrade increases considerably with increase in compactive effort; (2) with vibrating rollers and sandy soils, higher density can be achieved than the modified AASHTO maximum density; (3) the strength of soil at modified AASHTO compaction can be measured reasonably accurately from other characteristics; (4) correlations, based on simple index properties, can substantially expedite the assessment of expected strength characteristics, by preventing the need for long tests.