The soil-rock mixture (SRM) is composed of large-sized rocks

soils as filling component and pores. The strength and deformation characteristics of SRM are closely related to its fine contents (soil contents). The skeleton void ratio

referred to as the void ratio of skeleton particles

is proposed to study the strength and deformation characteristics of SRMs with different fine contents. Firstly

a series of compaction tests was performed to establish a packing model for SRM accounting for gradation effects

from which the expression of skeleton void ratio was derived. Triaxial drained tests were also conducted to verify the effectiveness of the proposed skeleton void ratio in predicting the strength and deformation characteristics of SRMs with different fine contents. It is found that the skeleton void ratio

compared with global void ratio

can better reflect the real density of soil-rock mixture by revealing the intergrain contact state of soil and rock particles. The mechanical behavior of soil-rock mixtures with different fine contents can be reasonably predicted by testing pure soils or rocks.