Thomas J. Weaver and Dr. Kyle M. Rollins, Civil and Environmental Engineering
During earthquakes some soils loose their strength and flow like a liquid. This phenomenon is known as liquefaction. For many years, engineers and scientists have been studying the occurrence of liquefaction in silty and sandy soils. Recently, engineers and scientists have learned that gravelly soils can also liquefy under earthquake loadings. Many dams throughout the world have been constructed using gravelly soils. Much work is now being conducted in the United States to determine the safety of earthfill dams under earthquake loadings.
In order to determine a soils resistance to liquefaction, tests to determine soil properties must be performed. One soil property important in analyzing liquefaction resistance and soil response during an earthquake is shear wave velocity. Shear wave velocity tests are costly. Since these tests are expensive, some engineers have tried to correlate the shear wave velocity of gravels with results from other field tests.
Under the direction of Dr. Kyle Rollins, I have correlated the shear wave velocity of gravels with their geologic age, current stress state, and results from the Becker Penetration Test. The Becker Penetration Test consists of a large diameter steel tube being pounded into the ground by a diesel powered hammer. To correlate Becker Penetration Test results with shear wave velocity, raw data from the Becker Penetration Test was converted to a standard penetration value. After the three variables(geologic age, stress state, standard penetration value) were determined at various sites, regression analyses were performed to determine how well these variables correlated with measured shear wave velocities. As part of the regression analyses, a function that best fits the scattered data was developed. We have found a good correlation does exist between the three variables and shear wave velocity.
Figures 1 and 2 present the results of the analysis. Although not apparent by viewing Figures 1 and 2, gravels of different ages which have the same standard penetration blow count and current stress state differ greatly in the predicted shear wave velocity. It is hoped that results from this research will benefit the U.S. Bureau of Reclamation as they determine the safety of earthfill dams.
