Revisit to Liquefaction of Gravelly Soils Compared with Sandy Soils

Natural gravelly soils liquefied from time to time during previous earthquakes were all well-graded and of much higher dry density than poorly-graded sands, though their S-wave velocity V_s and SPT N-value were as low as liquefiable sands. A series of systematic pressure chamber tests conducted on a set of granular soils indicate that N and V_s of well-graded gravels are correlated with soil densities quite differently from those of sands and highly dependent on grain-size curves or uniformity coefficient C_u. In laboratory triaxial tests, CRR-values for well-graded gravelly soils corresponding to the initial liquefaction, for axial strain ε_DA=5%, are not much different from those for poorly-graded sands of the same relative density. On the other hand, post-liquefaction residual strength for larger strains, ε=20% for example, is obtained about 10 times larger than poorly-graded sands indicating that gravelly soils are much more resistant to post-liquefaction large-strain failures. CRR~N correlations for gravelly soils developed by triaxial tests on intact samples and liquefaction case-histories are discussed in view of the basic laboratory test results.