Influence of anisotropic properties of coarse gravel in calculation of dam slopes stability

Abstract

Gravel-pebble soil laid into the dam's body during layer-by-layer compaction acquires pronounced anisotropic properties, which are manifested in the difference in filtration, deformation, and strength characteristics of soils in mutually perpendicular directions. The phenomena of filtration anisotropy of soils are well known, and the solution of filtration problems, as a rule, is carried out taking into account anisotropy, the phenomenon of deformation anisotropy in soils has been studied less, and the main work on deformation anisotropy is related to the stratification of rocks. The layering of rocks is also reflected in the difference in strength properties. Neither deformation anisotropy nor strength anisotropy have been sufficiently investigated in bulk soils, which determines the relevance of this work. Taking into account the anisotropy of the deformation and strength characteristics of bulk soils will allow for a more accurate analysis of the stress-strain state of soil dams and the stability of their slopes.The study included experimental research of strain-induced anisotropy of coarse gravel in a large, triaxial instrument. It was found that, since the Young modulus for coarse gravel compacted after each layer is higher along the stratification axis than along the direction normal to stratification axis, i.e. Ex > Ey, the strength characteristics of soil (shear angles) are also different in different directions, but φx < φy. As the compressive stresses increase, the anisotropic factor reduces. The problems of slopes stability have been solved with and without consideration of anisotropy for dams of different designs and heights. Adjustment factors have been derived based on Kywith consideration of anisotropy/Kywithout consideration of anisotropy ratio to address strength anisotropy in the calculation of slopes stability. The adjustment factor of kKan for the dams with central watertight elements can achieve 0.92. The problems of stress-strain behavior for earth dams (Plaxis) have been solved with and without consideration of the anisotropic properties of coarse gravel. It was found that accounting for the anisotropic properties of gravel yields 7-10% reduction of horizontal displacements in the dam.