Study on the determination mechanism of the compression wave velocity of soil-rock mixture considering the effect of soil-rock interface

The wave velocity of Soil-Rock Mixture (SRM) is an important index for seismic effect analysis of natural SRM site and quality evaluation of artificial SRM project. In order to clarify the compression wave velocity deter-mination mechanism of SRM, a ternary mesoscale model of SRM including soil matrix, rock blocks and Soil-Rock Interface (SRI) was established based on the "Divide & Fill" method and calculated with 2D FEM code. The contact stiffness model was used to characterize SRI, and three typical contact models were assumed: ideal contact, ITZ (Interfacial Transition Zone) contact and cracked contact. The calculation formula of the compression wave velocity of SRM under ideal contact condition was given. The influence mechanisms of ITZ and crack on wave velocity under non-ideal contact conditions were expounded and the multi-factor competition mechanism for the influence of macro parameters such as rock content on the wave velocity was further clarified. These conclusions were verified by the wave velocity test experiments of loess-sand mixture under different pressure conditions. Finally, the damage variable of SRM was calculated according to the compression wave velocity under ideal and actual SRI, and was proposed to be one of the indexes to evaluate the quality of SRM.