Bbn Corporation

Bill Watters

William R Hamblen

Frank Berkman

The in-situ measurement of the shear modulus of a surface layer of soil ( ) is performed by apparatus in which a contact foot ( ) with a preselected downward bias force engages a defined area of a region of soil. A drive transducer ( ) shakes the contact foot ( ) vertically and sensing transducers ( ) determine the force applied to the foot ( ) and the resulting movement of the foot ( ) and generate respective first and second output signals. The in-phase movement responsive output signal is analyzed in relation to the force signal to obtain a measurement of a single parameter which is representative of the stiffness provided by the soil ( ). The shear modulus as well as the void ratio of the soil can be calculated from the stiffness. The drive transducer ( ) is energized by an a.c. signal which progressively varies in frequency over a preselected band with the rate of change also varying with frequency thereby providing a greater force spectrum content at lower frequencies than at higher frequencies in the band, while maintaining a substantially constant force magnitude.

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Gloucester, MA, United States of America

Bill Watters