Ultrasonic Velocities and Strength of Frenchman's Flat Alluvium

摘要

Compressional and shear wave speeds and longitudinal stress and strain were measured under undrained triaxial stress for Frenchman's Flat alluvium. Nine of the thirteen samples were tested in as-received conditions and four were re-constituted in various ways. No difference in the measured properties of the virgin and reconstituted samples was found. Maximum shear stresses less than 0.1 MPa were observed at longitudinal strains up to 7 to 10% in the fully saturated samples at a confining pressure of about 10 MPa. Further increase in longitudinal strain resulted in a dramatic increase in the maximum shear stress to values greater than 3 MPa. This increase in strength is a result of an increase in effective stress as the sample dilates and the pore fluid pressure decreases. Sound speeds for compressional (v/sub p/) and shear (v/sub s/) waves increased dramatically during hydrostatic loading, then remained constant under triaxial loading to more than 10% axial strain. Under triaxial loading conditions, v/sub p/ ranged between 1.77 and 2.48 km/sec with an average v/sub p/ = 2.18 +- 0.23 km/sec. v/sub s/ ranged from 0.74 to 1.02 km/sec with v/sub s/ = 0.90 +- 0.10 km/sec. The ratio v/sub p//v/sub s/, taken for each sample, ranged from 1.82 to 2.71 with v/sub p//v/sub s/ = 2.39 +- 0.30. No significant changes in v/sub p/ and v/sub s/ were observed in the dilatant region. (ERA citation 06:005500)