CORRELATION BETWEEN STRENGTHS AND PENETRATION RESISTANCES FOR GRAVELLY SOILS

抄録

High-quality undisturbed gravel samples, 30 cm in diameter and 60 cm high, are obtained by the in-situ freezing method at four sites. Both the undrained cyclic shear strength and drained shear strength of these samples are measured by using a large scale triaxial test apparatus. The standard penetration test (SPT) and large penetration test (LPT) are conducted at each site to obtain possible correlations between their penetration resistances and the in-situ shear strengths. The data of gravels obtained by other investigators are also reviewed and discussed. The laboratory test results and the review of previous studies lead to the following conclusions. (1) The liquefaction resistance (the shear stress ratio required to cause 2 or 2.5% double amplitude axial strain in 15 load cycles) of the high-quality undisturbed gravel samples shows a good correlation with the value of N_L1(normalized for the effective vertical stress of 1 kgf/cm²) over a range of N_L1 between 20 and 50 in such a way that the liquefaction resistance increases with an increase in N_L1. The correlation appears to be independent of effective vertical stress. (2) The liquefaction resistance of the high-quality undisturbed gravel samples is overestimated particularly for N₁-values larger than 30, if correlations between the liquefaction strength and the blowcount from the conventional SPT obtained for sands are directly applied.