Liquefaction Strengths of Poorly-Graded and Well-Graded Granular Soils Investigated By Lab Tests

Abstract

In order to understand differences in liquefaction behavior of well-graded gravelly soils compared to poorly-graded sands, a series of lab tests was performed on granular soils with different particle gradations or fines content having different relative densities reconstituted in laboratory. Large soil container tests indicated that SPT N-value of well-graded gravels of relative density higher than 50% is considerably larger than that of sand of the same relative density, resulting in lower liquefaction strength of gravelly soils than that of poor-graded sand under the same corrected N-value, N1, for N1 > 25−30. Cyclic triaxial tests on reconstitutes specimens indicated that relative density can serve as a proper index to uniquely evaluate liquefaction strength corresponding to 5% DA strain for variety of granular soils having different gradations. In contrast, post-liquefaction undrained residual strength for larger strain is not uniquely determined by relative density but largely dependent on particle gradations. Also found was that the liquefaction strength clearly reduces with increasing fines content Fc both in well-graded and poorly-graded soils but the reduction occurs in a smaller range of Fc in accordance with smaller critical void ratio for well-graded soils than for poorly-graded sand. Increase in Fc also reduces post-liquefaction residual strength of granular soils particularly for higher relative density. Greater reduction occurs in smaller Fc range for well-graded soils than for poorly-graded sand because of the difference in the critical void ratio.