Robert Henke

In Situ Nonlinear Inelastic Shearing Deformation Characteristics of Soil Deposits Inferred Using the Torsional Cylindrical Impulse Shear Test

This article summarizes preliminary field evaluations of a new in situ geotechnical test, the torsional cylindrical impulse shear test. The impulse shear test provides, for soil deposits, detailed information on in situ nonlinear inelastic shearing deformation characteristics needed for dynamic geotechnical earthquake analysis procedures. The test addresses the issue of obtaining such information in a practical manner without disturbing the tested soils excessively. Herein, we present soil characteristics inferred from results of impulse shear tests conducted at four sites using a field prototype testing system. One of the sites is the I-10/La Cienega Blvd. undercrossing in Los Angeles, where a freeway structure collapsed during the 1994 Northridge earthquake, and another is the National Geotechnical Experimentation Site on Treasure Island in the San Francisco Bay. The four sites cover a broad range of soil conditions relevant to earthquake engineering. These include soft to medium-stiff clays and saturated loose sands. Comparisons between our results and published information suggest that the impulse shear test is a promising means for obtaining in situ nonlinear inelastic shearing deformation characteristics of soil deposits. Manuscript received 15 November 2000.

Selected Issues Regarding the Torsional Cylindrical Impulse Shear Test

This article discusses selected issues addressed by a 2002 field torsional cylindrical impulse shear testing program carried out at the National Geotechnical Experimentation Site on Treasure Island in the San Francisco Bay. The impulse shear test is a new in situ geotechnical testing method that provides detailed information, for soil deposits, on in situ nonlinear inelastic shearing deformation characteristics needed for dynamic geotechnical earthquake analysis procedures. One purpose of the Treasure Island testing program was to initiate a definitive verification of this capability. Previous field testing programs we had carried out were preliminary evaluations that focused largely on operability issues. Additionally, recent findings suggest that the impulse shear test may have the potential for providing reasonably precise indications of in situ resistances of soil deposits to liquefaction and related deformations. A second purpose of the Treasure Island testing program was to further explore this possibility. The Treasure Island site is a particularly relevant site for the subject investigation. The site consists of a layer of saturated loose sandy soils underlain by a medium-stiff clay layer. Such a sequence has proven to be extraordinarily hazardous during past earthquakes. The clay layer can amplify ground motions greatly, and the sandy layer tends to liquefy. The results of our testing program suggest that the impulse shear test is (1) a viable means for estimating in situ nonlinear inelastic shearing deformation characteristics of soil deposits and (2) a promising approach for obtaining reasonably precise indications of in situ resistances of soils to liquefaction and related deformations. Manuscript received 3 January 2003.