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|Title:||Cyclic rotation of principal planes to investigation liquefaction of sands|
|Authors:||United States. Assistant Secretary of the Army (R & D)|
Donaghe, Robert T.
Gilbert, P. A.
Principal stress rotation
|Publisher:||Geotechnical Laboratory (U.S.)|
Engineer Research and Development Center (U.S.)
|Series/Report no.:||Miscellaneous paper (U.S. Army Engineer Waterways Experiment Station) ; GL-83-24.|
Abstract: This report contains a description of a new hollow cylinder soil testing device and results of a preliminary testing pr ogram utilizing the device. The objective of the, investigation was to design and fabricate a testing device that would apply synchronized cyclic axial and torsional stresses to a hollow cylinder saturated sand specimen in such a manner that there is a continuous and systematic rotation of principal stress axes. Another was to conduct a preliminary testing program and to investigate the effects of cyclic rotation of principal stresses in saturated sand specimens in terms of the susceptibility of these materials to earthquake induced liquefaction. Cyclic triaxial tests do not provide for any continuous principal stress rotation during shear (the maximum principal stress does alternate between horizontal and vertical planes) and other tests such as the cyclic simple shear test provide only limited rotation (±4 deg). Since earthquakes may produce random rotation of principal stresses in situ, a laboratory test having the capability to study principal stress rotation is needed. In the test developed herein, principal stress axes rotate through 360 deg each loading cycle and every plane within the specimen is loaded with the maximum shear stress each cycle. This means that the weakest plane in anisotropic materials will be loaded as intensely as any plane; therefore, the strength and stability of the material will naturally be affected and the consequent effect of anisotropy will be included in the cyclic principal stress rotation test. In the past this effect has only been estimated and the stability of materials determined in the cyclic triaxial test reduced by an empirical factor as a result. In general, cyclic triaxial loading applies maximum shear stress to only one pair of orthogonal planes in a specimen and they are unlikely to be the weakest. Therefore, in anisotropic materials the cyclic triaxial test, and generally any test which does not effect principal stress rotation, will indicate too high a strength. The objectives of the investigation were achieved by designing and building an electropneumatic loading system for an existing hollow cylinder test chamber that satisfied the complex loading requirements and by performing five consolidated-undrained hollow cylinder cyclic principal stress rotation tests on saturated specimens of Monterey No. 0 sand compacted to 50 percent relative density and consolidated under a confining pressure of 1.0 kg/cm². Results of the tests indicate that principal stress rotation produced lower laboratory cyclic strength than either cyclic triaxial or cyclic simple shear tests. Additional testing on hollow cylinder cyclic triaxial and simple shear tests are needed over a broader range of variables to verify this finding.
|Rights:||Approved for public release; distribution is unlimited.|
|Appears in Collections:||Miscellaneous Paper|
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