Empirical Correlation Between Penetration Resistance and Internal Friction Angle of Sandy Soils

Abstract

A series of drained triaxial compression tests were performed on high-quality undisturbed samples of sandy soils for the determination of the angle of internal friction (Φd). The high-quality undisturbed samples were recovered by the in-situ freezing sampling method (FS sample). The angle of internal friction for the high-quality undisturbed samples (Φd(Fs)) was compared with calculations from the empirical equations proposed by many investigators previously using the N-value of the standard penetration test (SPT). It was found that the angle of internal friction for the high quality undisturbed sand samples was much higher than that estimated from the proposed empirical equations. In order to take into account the effects of the confining stress on the SPT N-value, the measured N-value was normalized at an effective overburden pressure of 98 kPa (1 kgf/cm2) using the equation proposed by Liao and Whitman (1986). The normalized N-value, N1, was induced to relate the angle of internal friction for the high-quality undisturbed sand samples. A fairly good correlation between the N1 value and the Φd(Fs) was established. Finally, based on the test results, a simple equation (Φd(FS)=(20N)0.5+20) was proposed to relate the N1 value and Φd(FS) of sandy soils in the range of N1 between 3.5 and 30, for this study. The relationship between the angle of internal friction for the high-quality undisturbed gravel samples (Φd(GV)) and the penetration resistance was also discussed. A new parameter of NL1 was introduced in order to relate to Φd(GV), where NL1 is the penetration resistance of the large scale penetration test (LPT) normalized at an effective overburden pressure of 98 kPa (1 kgf/cm2), using a similar equation to that proposed by Liao and Whitman (1986). Although data is limited, a correlation between NL1 and Φd(GV) similar to that proposed in this study for sandy soils was found.