Monitoring Structural Deformation at Pacoima Dam, California Using Continuous GPS

Jeffkey A. Behr, Kenneth W. Hudnut and Nancy E. King

Abstract:	Agencies responsible for dam safety have long used conventional surveying methods to measure the displacements of benchmarks as part of dam monitoring programs. Such surveys have provided infrequent though precise estimates of a dam’s motions. With the development of high precision GPS methods to monitor plate tectonic motions and crustal deformation rates, an alternative method for monitoring such structural motions became available. While high- precision GPS approaches the horizontal positioning capability of conventional surveying methods, its great benefit lies in a much higher temporal resolution and nearly unattended continuous operation. In September 1995, Pacoima Dam, located in the San Gabriel Mountains north of Los Angeles, California, was instrumented with a triad of continuously operating GPS receivers to test the feasibility of applying these techniques to the field of structural monitoring. Nearly three years of data have been analyzed from this sub-array to provide quarter-daily estimates of station-to-station baseline lengths. Quantitative methods were assessed to allow the identification of a number of outlying data points that could be misinterpreted as GPS station motion in a real-time system. Examination of the derived baseline time series indicates that Pacoima Dam is experiencing an annual cycle of upstream-downstream (E-W) motion at the center of the dam arch of approximately 15-18 mm peak-to-peak amplitude. Comparison of motion to daily regional temperature records strongly indicates that the dam responds to annual and shorter-period ambient temperature variations. Spectral methods are used to model this relationship to allow a more accurate estimation of the thermoplastic behavior of the structure.
Published in:	Proceedings of the 11th International Technical Meeting of the Satellite Division of The Institute of Navigation (ION GPS 1998) September 15 - 18, 1998 Nashville, TN
Pages:	59 - 68
Cite this article:	Behr, Jeffkey A., Hudnut, Kenneth W., King, Nancy E., "Monitoring Structural Deformation at Pacoima Dam, California Using Continuous GPS," Proceedings of the 11th International Technical Meeting of the Satellite Division of The Institute of Navigation (ION GPS 1998), Nashville, TN, September 1998, pp. 59-68.
Full Paper:	ION Members/Non-Members: 1 Download Credit Sign In