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.
Directional-dependence in the mechanical characteristics of sand: a review
The majority of granular soil is anisotropic material and it exhibits stress–strain variations depending on principal stress directions. Such directions acting on granular deposits vary with in situ loading conditions. Many experimental, numerical and analytical studies on anisotropy effects, as represented by principal stress rotation, on sand behaviour have been reported in the literatures, however, no attempt has been made to present an overview of this issue. Therefore, this review presents a comprehensive overview of the effect of anisotropy on sand behaviour, including the fabric effect, different fixed direction of principal stress and continuous rotation of the principal stress effects on the stress–strain response of sand in addition to bearing capacity under an inclination bedding plane. This review indicates that sand strength is affected strongly by the direction of principal stress, and strength decreases as the inclination increases, reaching a minimum value in the range of α = 60–90°, although some studies report some increase in strength at α = 90°. Moreover, the rotation of principal stress results in progress deformation with most of it occurring during the first cycles. Consequently, it is highly recommended to take anisotropy into consideration for any proper design of geotechnical problems. Ignoring anisotropy may lead to failure due to the overestimation of strength.
Time and Heritage
As a historian studying what can be considered a form of intellectual history, I have slowly come to adopt Michel de Certeau’s observation made at the end of the 1980s that ‘objectifying the past, for the last three centuries, has undoubtedly left unconsidered time within a discipline that has continued to use it as a taxonomic instrument’. To a certain degree, time has become commonplace for the historian who has preserved or instrumentalized it. It is not considered because it is inconceivable, but because we do not think of it or, more simply, we do not think about it. As a historian attempting to pay attention to the time I’m living in, I have thus, like many others, noticed the swift development of the category of the present until it has become obvious that the present is omnipresent. This is what I refer to here as ‘presentism’.