Date of Award

Spring 1981

Project Type

Dissertation

Program or Major

Engineering

Degree Name

Doctor of Philosophy

Abstract

The testing program described in this dissertation was performed to develop an acoustic method for identifying the fabric of saturated medium to fine sand samples, and their related resistance to liquefaction. Three methods of preparation, that produced repeatably different preferred long grain axis orientations, were used to prepare laboratory samples (6.8" high by 2.7" in diameter) of a uniform, angular sand.

Acoustic signatures were obtained, for both dry and saturated samples, using compressional and shear wave transducers. The latter were developed specifically for the test program and included a 4 bender bimorph array as the shear wave crystal. The samples were then tested to liquefaction under undrained, stress controlled, cyclic triaxial conditions.

Results of the investigation revealed that the compressional wave velocity and attenuation of the saturated triaxial sand samples were reliable indicators of sample fabric, albeit they were very sensitive to the level of saturation. In turn, these acoustic parameters were found to be directly related to the liquefaction resistance of the same laboratory samples. The effect of stress history on the liquefaction resistance of a test sample was also predicted by the above acoustic parameters. The results of tests employing the newly developed acoustic transducers confirmed the initial compressional wave results as well as providing information on the shear wave velocity of the test sand fabrics. This more complete acoustic signature permitted the computation of the Shear Modulus, V(,p)/V(,s), and Poisson's Ratio for the laboratory samples. Each of these parameters was found to be a sensitive indicator of the method of sample preparation, and the resulting acoustic rigidity. Shear wave velocity was observed to decrease with increasing moisture content and decreasing effective stress. The effect of overconsolidation was seen as an increase in the shear wave velocity.

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