Effects of fine aggregate content on the mechanical properties of the compacted decomposed granitic soils

Decomposed granitic soil is widely used as the subgrade material in Korea. The mechanical behavior of the soil can differ depending on the fine aggregate content of the soil. Due to particle crushing during loading and compaction, the soil may behave as either cohesive or cohesionless. In order to evaluate the effects of fine aggregate content on the mechanical property tests were made by using samples with the five different fine aggregate contents of 10, 20, 30, 40, and 50% by weight. Results of the triaxial tests showed that as the percentage of the fine aggregates decreased, the cohesion decreased as well as the internal friction angle increased. In the direct shear test, the soils containing lower amount of fine aggregates exhibited that the shear strength was considerably reduced after it reached the peak value. Comparably, soils with the high fine aggregates showed that the shear strength was quite constant after the peak strength. The critical state friction parameter showed that the parameter decreased with an increase of the fine aggregate content. Results of the triaxial and direct shear tests indicated also that the fine aggregate content of 30% could be one indicator for soil materials behaving either as sand or as clay materials. Thus fine aggregate content, less than 30% by weight, could be more obtainable for the subgrade materials when leading also to the increased stability of the roads. With the lower fine aggregate content the soils then also show similar and better characteristics of sands not clays. Further studies are recommended on understanding of the mechanical behavior of the decomposed granitic soils. (C) 2004 Elsevier Ltd. All rights reserved.