GYRATORY SHEAR APPARATUS, DESIGN, TESTING PROCEDURES, AND TEST RESULTS ON UNDRAINED SAND
The redistribution of water content and density-within-specimen was measured in undrained sand subjected to cyclic simple shear (X) tests and gyratory shear tests, both tests types using a gyratory apparatus. Measured redistribution of density shows clearly that loose and medium dense specimens are compacted in zones adjacent to the rigid top and bottom boundaries and are loosened in zones along midplane and adjacent to membrane. With increasing number of cycles, redistribution and softening in loose and medium-dense specimens continue until steady-state deflections develop. In terms of relative density of elements, redistribution can be expressed by standard deviaton, which is from 2.0 to 2.5 percent for specimens of all densities as placed, and which increases to a maximum of about 10 percent for loose specimens when cycled to steady-state displacements. Significant cyclic softening also develops in dense specimens, although determination of redistribution by freezing and cutting is too crude for measuring magnitude. When steady displacements are reached in X tests, each time the shear stress cycles through zero, the cyclic peak pore pressure increases with a sharp peak almost equal to the effective vertical stress at start of test. In Y tests, the pore pressure rises to a maximum that is about two-thirds of effective vertical stress at start of test. When a specimen softens during a cyclic test, the displacements change from a pattern which indicates that the sand responds with a constant shearing resistance to an entirely different pattern with an almost sudden and great drop in shear strength followed by an equally sudden increase. This pattern reflects alternate development of liquefaction and dilation within one or more zones of specimen. Urgently needed are more precise measurements of redistribution during first stage of cyclic tests, while cyclic peak pore pressure rises to its maximum. Necessary accuracy could probably be achieved with cyclic triaxial tests and by freezing and cutting specimens into horizontal slices. /Author/
- Sponsored by the Waterways Experiment Station Geotechnical Laboratory.
Harvard UniversityCambridge, MA United States 02138
- Casagrande, A
- Rendon, F
- Publication Date: 1978-10
- Features: Figures;
- Pagination: 99 p.
- TRT Terms: Bitumen; Density; Dilation; Gyratory testing machines; Liquefaction; Moisture content; Pore pressure; Sand; Saturated soils; Shear tests; Tank trucks; Test procedures; Testing equipment
- Old TRIS Terms: Bituminous distributor; Gyratory tests; Liquefaction (Soil); Undrained
- Subject Areas: Geotechnology; Highways;
- Accession Number: 00189330
- Record Type: Publication
- Report/Paper Numbers: Tech Rpt S-78-15 Final Rpt.
- Contract Numbers: DACW39-74-E0026
- Files: TRIS, ATRI
- Created Date: Mar 28 1979 12:00AM