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Title: Fast triaxial shear device evaluation
Authors: University of Central Florida. Department of Civil Engineering and Environmental Sciences.
Carroll, William F.
Keywords: Dynamic soil properties
Shear strength
Loading rate effects
One-dimensional wave analyses
Triaxial shear tests
Fast triaxial shear device
Soil mechanics
Publisher: Structures Laboratory (U.S.)
Engineer Research and Development Center (U.S.)
Series/Report no.: Technical report (U.S. Army Engineer Waterways Experiment Station) ; SL-88-2.
Description: Technical Report
Abstract: This report documents the most current evaluation of the US Army Engineer Waterways Experiment Station fast triaxial shear device (FTRXD). It describes the FTRXD, pertinent properties of the soil tested in the FTRXD, preliminary results from the testing, and a onedimensional (1-D) nonlinear wave analysis of the FTRXD specimen. The FTRXD is a triaxial cell which loads its 0.75-inch-diameter by 1 .5- inch-long cylindrical specimen by displacing the top of the specimen downward at a rapid rate. The specimen may be subjected to confining pressures up to 1,000 psi. Displacement, load at the top of the specimen, and load at the bottom are measured as continuous functions of time. To date, specimens have been brought to failure in as little as 2 milliseconds. Loading is accomplished with a piston and cylinder assembly powered by compressed nitrogen. Soil from the CARES-Dry test site on Luke Gunnery range in Arizona was used in the evaluation. It classifies as a clayey sand (SC) in the Unified Soil Classification System. It exhibits a principal stress difference (PSD)-axial strain curve which may be represented by a function which is initially linear, then hyperbolic. The preliminary load-time data from the FTRXD revealed larger loads recorded at the top than at the bottom of the specimen. The differences were less than 1 percent for tests with durations of 2 to 120 seconds, but increased to 40 percent for tests with a duration of 2 milliseconds. Part of the difference is attributed to wave effects in the specimen, but a major part is due to the dynamics of the FTRXD. Additional significant effects from the dynamics of the FTRXD were. recorded by the moving load cell at the top of the specimen. The 1-D wave analysis of the specimen, first employing an initially linear, then hyperbolic stress-strain curve for the specimen, and having the top of the specimen displace downward in the manner measured during testing, provided axial stress at the top and bottom of the specimen. These were plotted against gross strain, the displacement of the top divided by the specimen length. The specimen's true stress-strain curve may be determined from these plots, although the details of the determination depend on the details of the displacement-time data of the top of the specimen. For specimens brought to failure in 20 milliseconds or more, the top and bottom stress intersect repeatedly when plotted against gross strain. The intersections trace the specimen's true stress-strain curve accurately. For faster tests, the top and bottom stress intersect infrequently, if at' all. However, they are an upper and lower limit of the actual stress, which might be located as a function of these bounds.
Rights: Approved for public release; distribution is unlimited.
Appears in Collections:Technical Report

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