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Title: Rate effects in shear for CARES-Dry soil
Authors: University of Central Florida. Department of Civil Engineering and Environmental Sciences.
Carroll, William F.
Keywords: CARES-Dry clayey sand
Shear strength
Dynamic soil properties
Loading rate effects
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-88-9.
Description: Structures Report
Abstract: Thirty-six individual specimens of CARES-Dry soil were tested in the fast triaxial shear device (FTRXD) at three confining pressures and at six test velocities. The slowest were static, unconsolidated, undrained triaxial tests. The fastest (9.0 ips) were the fastest that could be obtained while maintaining constant deformation velocity. The FTRXD performed well. Load and displacement as a function of time were measured accurately. Constant velocities were achieved. Procedures developed to prepare specimens, mount them in the FTRXD, and assemble and operate the FTRXD were reasonably efficient. The new upper load cell was accurate, durable, and easy to use. During this test series, discrepancies between the upper and lower load cells were essentially eliminated, due in part to the new upper load cell. Neither the dynamics of the FTRXD nor specimen inertia influenced the test results noticeably, despite the fact that some specimens were brought to failure in 2 to 3 msec. In the fastest tests, a small lag in the response of the lower load cell occurred, the time it took for a disturbance at the top of the specimen to propagate to the bottom. Thus using faster test velocities or longer test specimens will require that specimen inertia be taken into account. The FTRXD does permit assessing rate effects of soils subjected to triaxial shear throughout meaningful ranges of principal stress difference and nominal axial strain. During deformation, the CARES-Dry soil appeared to pass through three behavior modes: initial grain structure response, grain structure collapse, and plastic shear failure. During the first mode, the grain structure of the specimen is intact and the relationship between principal stress difference and nominal axial strain is essentially linear, increases predictably with increasing confining pressure, and is unaffected by deformation velocity at high confining pressure. At low confining pressure when deformation velocity is high, specimen behavior was varied and inconclusive. The second and third modes show the same effects from deformation velocity. The relationship between principal stress difference and nominal axial strain is highly nonlinear during the second mode but approaches linearity during the third. In both modes increasing confining pressure increases the magnitudes of principal stress difference in a predictable manner, and there is a modest increase in the magnitude of principal stress difference at high confining pressure due to deformation velocity. No rate effects were observed in these modes at lower confining pressures. The CARES-Dry soil at the moisture content and dry density tested has linear Coulomb failure envelopes. The envelopes were different for different nominal axial strains but were unaffected by deformation velocity within the range of the test series parameters.
Rights: Approved for public release; distribution is unlimited.
Appears in Collections:Technical Report

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