ISSN: 1945-7545
CODEN: GTJODJ
Published Online: 1 September 2012
Page Count: 14

Small-strain Cyclic Testing With Standard NGI Simple Shear Device

Mortezaie, Ahmad Reza
Project Engineer, Fugro Consultants, Inc., Los Angeles, CA

Vucetic, Mladen
Professor, Civil and Environmental Engineering Dept., Univ. of California, Los Angeles, CA

(Received 26 January 2012; accepted 8 June 2012)

Abstract

In the standard Norwegian Geotechnical Institute type of direct simple shear (NGI-DSS) test, the horizontal load cell record includes several false loads which do not represent the soil shear resistance. In the case of cyclic loading, the relative magnitude of these false loads increases as the cycle shear strain amplitude γ_c decreases. Consequently, in order to obtain accurate cyclic soil behavior at small γ_c, the NGI-DSS test records must be corrected to address the errors due to these false loads. This paper describes how, with the help of modern computer technologies, the false loads can be identified, quantified, and then subtracted from the load cell record. In an example, the proposed correction procedure is successfully applied to values of γ_c as small as 0.026 %. With this procedure, the accurate equivalent viscous damping ratio, the variation of the secant shear modulus with the number of cycles, and other cyclic properties can be obtained at γ_c as small as 0.01 %.

Keywords:
simple shear device, cyclic loading, testing errors, damping ratio, secant shear modulus, clay

Paper ID: GTJ20120007
DOI: 10.1520/GTJ20120007
ASTM International is a member of CrossRef.