CORRELATION OF PORE-PRESSURE B-VALUE WITH P-WAVE VELOCITY AND POISSON'S RATIO FOR IMPERFECTLY SATURATED SAND OR GRAVEL

TAKEJI KOKUSHO

ABSTRACT: Field data indicate that the P-wave velocity in sand or gravel is sometimes much lower than that of water, even if the soil is below the water table. It is well understood that a slight decrease in saturation normally evaluated by the B-value has a significant effect on undrained shear behavior like liquefaction of saturated soil. In the first part of this research, theoretical formulations of the B-value, P-wave velocity and Poisson's ratio are made by taking into account the decrease in bulk modulus of water due to a mixture of air bubbles. Then, computations are carried out using formulas based on the soil properties of a typical sand or gravelly soils and Masa soil from the Kobe area to make charts correlating the variables. These charts indicate that a small decrement in the B-value in the interval of B =1.0 to 0.8 will considerably decrease the P-wave velocity. Thus, the P-wave velocity which is easily measured in the field can serve as a convenient index to quantitatively evaluate the insitu soil B-value.

Key words:B value gravelly soils liquefaction P- wave Possson's ratio, undrained test (IGC: D7/E8/C8)