Fast Stacking and Phase Corrections of Shear Wave Signals in a Noisy Environment
Publication: Journal of Geotechnical and Geoenvironmental Engineering
Volume 134, Issue 8
Abstract
Hardware, software, and analysis of transient response of sources and receivers are presented for a piezoelectric bender element system designed to measure shear wave velocities in noisy environments. Signal-to-noise ratio is improved by signal stacking, wherein data vectors from many pulses are summed. A new fast-stacking algorithm enables signal quality to be improved much more rapidly than conventional stacking. Conventional stacking is accomplished by repeatedly sending an excitation pulse to a source, waiting for the signal and secondary reflections to pass the receiver and then introducing a subsequent excitation pulse. Using conventional stacking, it is important to wait for the signal and secondary reflections to die out before exciting subsequent pulses. In the new fast-stacking algorithm, a varied interval between consecutive pulses is used so that high quality signals can be obtained even if consecutive pulses are excited in rapid succession. Transient behavior of soil–bender interaction was characterized using closed-form analytical solutions of single-degree-of-freedom oscillators, numerical solutions using a beam-on-springs method, and measurements from an array of bender elements in a sand model. The time delay caused by soil–bender interaction was calculated to be half of the natural period of the bender element, and this theoretical time delay was supported by experimental data. This system makes it feasible to rapidly collect accurate shear wave velocity information so that transient changes in shear wave velocity can be monitored even if background noise is large.
Get full access to this article
View all available purchase options and get full access to this article.
Acknowledgments
The development and implementation of the bender element system was funded under NSF Award No. NSFCMS-0086566 through the George E. Brown Jr. Network for Earthquake Engineering Simulation (NEES). Seokhyeon Choi helped implement the hardware and develop the signal processing software. Advice regarding bender elements and preliminary testing in 1 laboratory specimens at Georgia Tech were provided by Jong-Sub Lee and Carlos Santamarina. The grouted pier test that contained the polar array of bender elements was performed by Yueying Bian and Tara Hutchinson under NSF Award No. NSFCMS-0513972. The work would not have been possible without the able assistance of UC Davis centrifuge staff Chad Justice, Nick Sinikas, Tom Coker, Ray Gerhard, and Peter Rojas.
References
Arulnathan, R., Boulanger, R. W., and Riemer, M. F. (1998). “Analysis of bender element tests.” Geotech. Test. J., 21(2), 120–131.
Bian, Y., Hutchinson, T. C., Wilson, D., Laefer, D., and Brandenberg, S. (2007). “Experimental investigation of grouted helical piers for use in foundation rehabilitation.” 4th Int. Conf. on Earthquake Geotechnical Engineering, Paper No. 1471.
Chopra, A. K. (2006). Dynamics of structures, theory and applications to earthquake engineering, 3rd Ed., Prentice–Hall International, Upper Saddle Hill, N.J.
Dyvik, R., and Madshus, C. (1985). “Lab measurements of using bender elements.” Proc., Advances in the Art of Testing Soils under Cyclic Conditions, ASCE, Reston Va., 186–196.
Fu, L., Zeng, X., and Figueroa, J. L. (2004). “Shear wave velocity measurement in centrifuge using bender elements.” Int. J. Phys. Model. Geotech., 4(2), 1–11.
Kramer, S. L. (1996). Geotechnical earthquake engineering, Prentice–Hall, Upper Saddle River, N.J.
Lee, J. S. (2003). “High resolution geophysical techniques for small-scale soil model testing.” Ph.D. dissertation. Georgia Institute of Technology, Atlanta.
Lee, J. S., Fernandez, A. L., and Santamarina, J. C. (2005). “S-wave velocity tomography: small-scale laboratory application.” Geotech. Test. J., 21(2), 336–344.
Lee, J. S., and Santamarina, J. C. (2005). “Bender elements: performance and signal interpretation.” J. Geotech. Geoenviron. Eng., 131(9), 1063–1070.
Lee, J. S., and Santamarina, J. C. (2006). “Discussion: Measuring shear wave velocity using bender elements by Leong, E. C., Yeo, S. H., and Rahardjo, H.” Geotech. Test. J., 29(5), 439–441.
Mazzoni, S., McKenna, F., Scott, M. H., and Fenves, G. L. (2006). Open system for earthquake engineering simulation user command-language manual. Pacific Earthquake Engineering Research Center, University of California, Berkeley, Calif.
Mindlin, R. D. (1936). “Force at a point in the interior of a semiinfinite solid.” Physics, 7, 195–202.
Morlet, J., Arens, G., Fourgeau, E., and Giard, D. (1982a). “Wave propagation and sampling theory—Part I: Complex signal and scattering in multilayered media.” Geophysics, 47(2), 203–221.
Morlet, J., Arens, G., Fourgeau, E., and Giard, D. (1982b). “Wave propagation and sampling theory—Part II: Sampling theory and complex waves.” Geophysics, 47(2), 222–236.
Santamarina, J. C., and Fam, M. A. (1997). Discussion of “Interpretation of bender element tests (discussion), by Viggiani, G., and Atkinson, J.H.” Geotechnique, 47(4), 873–877.
Santamarina, J. C., and Fratta, D. (2005). Discrete signals and inverse problems. An introduction for engineers and scientists, Wiley, West Sussex, U.K.
Sarma, M. S. (2001). Introduction to electrical engineering, Oxford Univ. Press, Oxford, U.K.
Skopek, J. (1961). “The influence of foundation depth on stress distribution.” Proc. 5th Int. Conf. on Soil Mechanics and Foundations Engineering, Vol. 1, Dunob, Paris, 815–818.
Vucetic, M., Lanzo, G., and Douroudian, M. (1998). “Damping at small strains in cyclic simple shear test.” J. Geotech. Geoenviron. Eng., 124(7), 585–594.
Wang, Y. H., Lo, K. F., Yan, W. M., and Dong, X. B. (2007). “Measurement biases in the bender element test.” J. Geotech. Geoenviron. Eng. 133(5), 564–574.
Information & Authors
Information
Published In
Journal of Geotechnical and Geoenvironmental Engineering
Volume 134 • Issue 8 • August 2008
Pages: 1154 - 1165
Copyright
© 2008 ASCE.
History
Received: Jul 12, 2007
Accepted: Dec 10, 2007
Published online: Aug 1, 2008
Published in print: Aug 2008
Authors
Metrics & Citations
Metrics
Citations
Download citation
If you have the appropriate software installed, you can download article citation data to the citation manager of your choice. Simply select your manager software from the list below and click Download.