Laboratory Qualification and Field Behavior Studies of Piezometers for Measuring Earthquake-Induced Pore Pressures

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Abstract: CMS-9709334, Pedro deAlba & Jean Benoit, University of New Hampshire When a saturated sand deposit is shaken by an earthquake, there can be a significant build-up of pore-water pressure, with consequent loss of rigidity and strength of the soil, often ending in actual liquefaction of the deposit, and major damage to structures. While pore-pressure buildup has been simulated in laboratory experiments, there is only one case currently available in which the development of these pore pressures to the point of liquefaction was measured in a field deposit under earthquake-induced strong-ground shaking. Unfortunately, the pore pressure records obtained in this case have certain unusual features, which has led some researchers to question their validity. Consequently, it is of primary importance to geotechnical earthquake engineers to obtain more records, in order to provide a final verification of mathematical models developed on the basis of laboratory and centrifuge testing. This research project involves an extensive laboratory and field study of piezometer designs in current use. In the laboratory, piezometer installation will be simulated in a test chamber, and piezometer response to dynamic pore pressure increases will be measured both in water alone and in saturated soil. Acceptable procedures for design, saturation and installation of piezometers will thus be identified. In the second phase, a field installation for periodically checking piezometer response will be developed. These second-phase tests will provide insight into the problem of response changes, if any, due to long-term biological or chemical interaction with the surrounding soil. The outcome of this project will be a set of guidelines for the design, manufacture, installation and long-term monitoring of piezometer arrays designed to obtain much-needed field data on pore pressure development during earthquakes. This project is being coordinated with a complementa ry research program headed by Dr. Behnam Hushmand of Hushmand Associates, California.