Evaluation of the Geo-Mechanical Parameters of the Interface Between Asphalt Concrete and Sand with Applying Direct Shear Test and Numerical Modeling

摘要

Asphaltic concrete has been used as waterproofing core in embankment dams, since 1948. In this application, the asphaltic core is surrounded by granular filter materials. The interaction of the asphaltic concrete and the granular materials has not been sufficiently investigated. In this paper the mechanical behavior of the interface between a natural smooth sand filter and asphaltic concrete at different levels of normal stresses and a constant shear strain rate has been studied. Small scale direct shear test has been conducted in this study, in which the shear surface is considered as the interface. Asphalt concrete specimens used in the shear test were cut in square shape (10×10×2.5 cm) from cylindrical specimen compacted by modified marshal compaction method. According to the direct shear test the interface constitutive parameters (cohesion, friction angle and shear stiffness) have been obtained. Using the parameters obtained from the direct shear tests, the numerical model of the test by applying FLAC3D Finite Difference software has been made, for which the Mohr-Coulomb constitutive parameters of the asphalt concrete have been obtained from back analysis using ABAQUS Finite Element software according to the conducted Marshal Test results on the asphalt. Utilizing the obtained parameters for both asphalt and interface, the normal stiffness of the interface has been extracted by back analysis with applying FLAC3D. It is shown that the shear stiffness and shear yield strength of the interface between sand and asphalt concrete, and the normal stiffness of the interface increase with increasing the normal stress level since driving direct shear test. The results of this study can help solving numerical problems of the interaction of asphaltic core and surrounding soil with considering more precise interface constitutive value, especially in the embankment dams with asphaltic core, which normal stress distribution on the asphaltic core varies through the different depths in the dam due to the hydrostatic pressure.