UBC Theses and Dissertations
The seismic cone penetrometer Rice, Anthony Henry
A static cone penetrometer was modified to incorporate a small diameter triaxial geophone package. This instrument was evaluated by obtaining downhole shear wave velocity profiles at selected research sites on the Fraser River Delta near Vancouver B.C. for the purpose of determining in-situ dynamic shear moduli. A second geophone package was added to the instrument to assess the accuracy of shear wave velocity measurements, and to determine a practical instrument configuration for routine field use. Shear wave characteristics, downhole velocities, signal repeatability and signal amplitude were studied, to evaluate the energy source and downhole receiver response, and to develop a rational testing procedure. Plank type signal sources were used exclusively and were found to be both satisfactory and convenient. Geophone response and receiver to soil coupling were excellent and identifiable shear waves were obtained to depths of 40 metres. Down rod signal transmission, signal repeatability and problems with high background noise levels were overcome by selective testing procedures and interpretation techniques. The results of this study indicate that a static cone penetrometer containing just a single geophone can provide a rapid and accurate method for carrying out a downhole shear wave velocity survey. The cone testing procedure allows superior shear wave records since it minimizes soil disturbance, provides excellent soil to receiver coupling and controlled receiver orientation. Combined with data from the cone bearing, friction and pore pressure measurement elements, the interpretation of in-situ static and dynamic soil properties, using a single test hole, is greatly enhanced.
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