Paper Information

Journal:   AMIRKABIR   Summer 2003 , Volume 14 , Number 55-E; Page(s) 215 To 220.


Author(s):  GHIASIAN H.*
* Iran University of Science and Technology Civil Engineering Department

A stress path triaxial testing study entailing compression extension and compression tests at constant major principal stress was performed on coarse Cambria Sand prepared with cross; anisotropic fabric in cylindrical specimens. Height-to-diameter ratios of 1.44 1.86 2.22 and 2.68 as well as different end conditions were employed to study the sand behavior in the range of applied effective confining pressures from 200 kPa to 4000 kPa. The compression test results were well comparable with those in the previous investigations as follow. 1) The tendency for dilation decreases with increasing confining pressure. 2) The friction angle decreases with increasing confining pressure. 3) The strain-to-failure increases with increasing confining pressure. 4) The strength increases with decreasing height-to-diameter ratio for specimens without lubricated ends. 5) The maximum rate of dilation occurs at the failure point. 6) Specimens with restrained ends exhibited higher strengths than specimens with free or lubricated ends. However the mode of failure appears to have been influenced seriously by the boundary conditions which in turn changes the stress-strain and volume change characteristics. In extension tests all specimens failed by development of shear planes either in the mid-section of the specimens in tests at low confining pressures (less than 1000 kPa) or under the cap in tests at higher confining pressures (more than 1000 kPa). Comparison of results from the extension tests shows that. 1) The strain-lo-failure in extension tests is smaller than that in compression tests. 2) The stress-strain curves after failure in extension tests become steeper as the confining pressures increase and their rates of stress decrease are much higher than those in compression tests. 3) The strain-to-failure increases as the confining pressure rises up to 1000 kPa and thereafter it decreases irregularly. 4) More meaningful and reasonable results are obtained from compression tests in which shear planes develop after peak failure than from extension tests in which shear planes develop before peak failure.

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