Fabric and strength anisotropy of cohesionless soils.

摘要

Fabric anisotropy is an important aspect of the fabric of granular materials. There is a great deal of evidence of fabric anisotropy occurring in soils in situ. The effects of anisotropy on the mechanical behavior of granular materials have received much attention. The major influence of anisotropy of granular soil is to give different volume change tendencies; i.e., it gives different stress deformations and strength behaviors for different directions of loading.; Using the newly developed stereology based on fabric tensors and digital image analysis methods, the anisotropy of sand was quantified. The inherent geometry anisotropy of specimens was prepared by pluviating dry sand through air into a tilting mound to give different directions of sample deposition with respect to the sample axes and applied principal stress directions. The deformation and strength behaviors of these anisotropic specimens were observed using direct shear tests. The induced anisotropy was also quantified during direct shear tests. The consistency and ability of fabric tensors were examined. Finally, the experimental knowledge on different degrees and nature of fabric anisotropy that could offer a better understanding of the relationship of strength anisotropy with fabric anisotropy of granular materials was provided.; This research has been carried out to achieve five major tasks related to fabric and strength anisotropy of cohesionless soils: (1) achievement of a set of devices includes Multiple Sieving Pluviation System, molds, angle supports, adjustable box for preparing sand specimen at different deposition angles, (2) preparation of 24 specimens with two kinds of sands at two relative densities and 432 images captured from these specimens, (3) automated the image process and analysis methods, (4) conducting of 64 shear tests at five deposition angles, three normal pressure with computer programs, and two relative densities for Ottawa sands and silica sands (60 tests of the deposit analysis and 4 of fabric evolution), (5) implementation of image analysis of anisotropic fabric including particle orientation, particle intercepts, and local void ratio analysis in quantifying the evolution of fabric anisotropy during depositing and shearing for Ottawa sands and silica sands.; This research has produced several new developments based on the results of experiments and analyses. Research found: (1) the anisotropy of orientation was the most obvious at a 45° deposition direction; (2) the shear strength of the granular materials was low with the deposition of 45°; (3) sand particles alignment during shear tests are noticeable in the shear plane; and (4) the entropy of local void ratio distribution agreed with stress-strain curves well for shear tests. These results provided a valuably experimental and theoretic knowledge of granular materials, which deposited at different directions, on the fabric anisotropy and strength anisotropy. Therefore, they offered a better understanding on the relationship between the fabric anisotropy and strength anisotropy of the granular materials. The relationship is very important for studying engineering properties of the soil and the mechanisms of soil behaviors under different loading conditions.