Design and in situ testing of a piezometer system to measure earthquake -induced pore -pressure changes
Pore pressure changes have been measured in fine sand deposits that are known to have liquefied during earthquakes. Some of the measured signals have not been similar to what was expected during earthquake-induced liquefaction. Using artificially generated signals, several investigators have attempted to determine if existing piezometer fields designed to measure earthquake induced pore pressure changes are operating correctly. The signals generated during one investigation were not similar to those expected from an earthquake. In another investigation, while the generated signals were similar to ones expected from an earthquake, the results were not reproducible; the generated signals damaged the aquifer being tested and damaged or destroyed some piezometers being tested. This thesis describes the design and field-testing of a piezometer system that allows in situ testing of the screens on the piezometer, and in situ calibration of the transducer. An intergral part of this system is a signal generating system that generates a signal with frequencies similar to those expected from an earthquake. The generated signal has been detected in piezometers at least 20 feet from the source and at depths of at least 15 feet deeper than the source. The signal has been demonstrated to be reproducible through time with no measurable damage to the aquifer or the piezometers. It has been possible to investigate the ability of an existing piezometer field to detect earthquake-like signals and to demonstrate changes over time of some piezometers in their ability to detect earthquake-like signals. A detailed procedure for installing a piezometer array for liquefaction studies is presented.
Engineering, Civil, Geotechnology, Geology
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