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Title: Investigation of plane strain shear testing. Report 3, Plane strain and triaxial compression tests on Painted Rock Dam material
Authors: Al-Hussaini, Mosaid M.
Keywords: Shear strength of soils
Publisher: Soils and Pavements Laboratory (U.S.)
Series/Report no.: Technical Report;S-71-2
Abstract: Abstract: Abstract: Tests were made to study the effects of strain conditions (i.e., axially symmetric and plane strain conditions), initial relative density, methods of consolidation (i.e., isotropic or Kₒ consolidation), and drainage conditions on the strength and deformation characteristics of a medium to coarse sand obtained from the subrounded sandy gravel termed Painted Rock material (from the Painted Rock Damsite, Gila River, Arizona). Another objective was to compare the strength and deformation of this material with those reported previously on a highly angular material called crushed Napa basalt. Two series of tests were conducted in this study. In the first series, the material was consolidated either isotropically or under Kₒ consolidation and sheared in a drained condition in triaxial compression using enlarged low-friction platens. In the second series, the specimens were consolidated isotropically or under Kₒ conditions and sheared in a drained condition in the WES high-capacity plane strain apparatus. A few consolidated-undrained triaxial compression and plane strain tests were also conducted. Initial relative densities of compacted specimens were 70 and 100 percent, and the effective confining pressures σ₃ at the end of consolidation were 60, 125, 300, and 425 psi. Test results showed that consolidated-drained triaxial compression specimens underwent larger axial strain at failure and more crushing of particles than plane strain specimens tested under comparable conditions. On the other hand, consolidated-drained plane strain specimens exhibited more compressional volumetric strain and had higher angles of internal friction than comparable specimens tested in the triaxial compression apparatus. The difference in the effective angle of internal friction was about 5 deg for dense specimens at a confining pressure of 60 psi and 2 deg for medium-dense specimens at a confining pressure of 425 psi. Results of drained triaxial compression and plane strain tests indicated that the values of the coefficient of earth pressure at rest and the axial strain and compressional volumetric strain at failure increased with decreasing density and increasing confining pressure. However, the effective angle of internal friction in both types of test decreased with increasing confining pressure and decreasing density. It is tentatively concluded that the consolidated-undrained plane strain tests showed greater negative pore water pressure and higher strength at failure than comparable triaxial compression tests. However for σ₃ varying between 60 and 300 psi, the effective friction angle under constant volume as calculated from Mohr's envelopes was constant (equal to 35 deg) for the Painted Rock material, was the same for plane strain and triaxial compression tests, and appeared not to be affected by the initial relative density or confining pressure. With regard to the effect of particle shape on the strength and deformation characteristics, test results showed that the Painted Rock material is less compressible and has a lower Kₒ value and higher initial tangent modulus than the crushed Napa basalt. On the other hand, test results on the Painted Rock material, while yielding practically the same angle of internal friction, showed lower axial strain and compressional volumetric strain at failure and less particle breakdown than the crushed Napa basalt tested under similar conditions. It is apparent that, with respect to compressibility, strength, and particle crushing, sound subrounded material can be considered superior to angular material for constructing embankments and dams.
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