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Investigations into the use of continuous shear wave measurements in geotechnical engineering

University of British Columbia

The research presented within this thesis covers the development of a means to continuously monitor shear waves in a laboratory triaxial apparatus and down-hole during seismic cone penetration. This work resulted from an investigation of ageing of Fraser River Sand using a bender element triaxial apparatus. Shear wave propagation times from bender elements were interpreted using published time domain and frequency domain techniques. These techniques provided similar results, but the variability exceeded the effect of ageing. The frequency domain and time domain techniques had different shortcomings. The two techniques could be combined to converge on a single frequency-dependent propagation time that was independent of the trigger signal waveform. This contribution was capable of resolving the small increase in shear wave velocity with age duration. The frequency domain component of the combined bender element technique could run continuously during an experiment. With this further contribution, it was possible to track the change in shear wave propagation time throughout an experiment. The continuous bender element testing was not observed to influence the effect of ageing. It was found that in Fraser River Sand ageing had a small effect on the shear wave velocity, no effect on the ultimate strength, and a significant effect on the shear stiffness over the intermediate small-strain range (observed from 0.01 to 1%). The normalized shear stiffness curve shifts to larger strains and becomes more brittle with ageing. The concepts of the developed continuous bender element method are not restricted to this equipment or even to just bender element testing. The continuous bender element method was adapted to down-hole seismic testing in the field. This contribution resulted in a continuous profile of the shear wave velocity during seismic cone penetration testing that is obtained without stopping the cone penetration. The developments in this thesis provide a continuous measure of the shear wave velocity through a laboratory experiment and a continuous profile with down-hole penetration depth, i.e. the shear wave velocity is measured every time the other parameters are taken.

Text

2014-10-28

Attribution-NonCommercial-NoDerivs 2.5 Canada

http://hdl.handle.net/2429/50908

Civil Engineering

University of British Columbia

UBCV

http://creativecommons.org/licenses/by-nc-nd/2.5/ca/