The anisotropy of Leighton Buzzard sand under general stress conditions
A hollow cylinder apparatus was used to investigate the inherent anisotropy and membrane penetration of Leighton Buzzard sand test-specimens. The degree of inherent anisotropy was found to be independent of the mean effective stress but dependent on the initial relative density of the test-specimen. In the vertical-tohorizontal directions, the degree of inherent anisotropy decreases with increasing relative density. A wet-pluviation, sample preparation technique produces cross-anisotropic test-specimens, with the degree of cross anisotropy independent of the initial relative density. The effects of membrane penetration (expressed in terms of the normalized unit membrane penetration) are found to be independent of the initial relative density and the mean effective stress.
The Membrane Effect in Triaxial Testing of Granular Soils
THE VOLUME CHANGE MEASUREMENTS OF GRANULAR SOILS IN TRIAXIAL TESTING ARE GNERALLY AFFECTED BY PENETRATION OF THE MEMBRANE ENCLOSING THE SOIL INTO THE VOIDS BETWEEN THE PARTICLES. THE MAJOR FACTOR INFLUENCING THIS PENETRATION HAS BEEN SHOWN TO BE THE PARTICLE SIZE OF THE SOIL BEING TESTED. ON THE BASIS OF THE RESULTS OF PREVIOUS INVESTIGATINS AND THE PRESENT STUDY, A RELATIONSHIP HAS BEEN FOUND BETWEEN THE MEMBRANE PENETRATION AND PARTICLE SIZE. THIS RELATIONSHIP MAY BE USED TO ESTIMATE THE MEMBRANE EFFECT FOR ANY GRANULAR SOIL. /AUTHOR/
Geomagnetic Polarity Epochs: Sierra Nevada Data, 3
Available paleomagnetic and radiometric results for about 60 igneous rocks 3.6 m.y. old or less are consistent with the following geomagnetic polarity epoch time scale: Brunhes normal polarity epoch, 0.0 to 0.85±0.15 million years; Matuyama reversed polarity epoch, 0.85±0.15 to 2.4±0.1 million years; Gauss normal polarity epoch, 2.4±0.1 to 3.35±0.1 million years; Gilbert reversed polarity epoch, 3.35±0.1 million years to (?). A brief interval of normal polarity (the Olduvai event) occurs within the Matuyama reversed epoch at about 1.9 m.y., and a brief interval of reversed polarity (the Mammoth event) occurs within the Gauss normal epoch at about 3.06 m.y. Data for twelve units from eastern California and Nevada, reported here for the first time, are particularly useful in defining the Gauss-Gilbert boundary and for recognizing the Mammoth event.