Triaxial compression tests were conducted on salt rock specimens with an interlayer to investigate its failure modes and failure mechanisms. Based on the force balance of an interlayer element and the transfer mechanism of shear stress on the interface

we established a differential equation of the interlayer's radial displacement. The theoretical formulas of shear stress on the interface

and stresses and strains of the interlayer were obtained by solving the differential equation. Numerical simulation was also performed to verify the accuracy of these stress formulas. Moreover

failure modes and failure mechanisms of salt rock with an interlayer are analysed by various failure criteria. It is found that shear stress on the interface and stress of the interlayer are not uniformly distributed

and their maximum values are typically in the edge and the centre. With regards to vertical splitting of the interlayer

calculations suggest that tensile stress or tensile strain in the horizontal direction occurs in the interlayer. A ring-shaped white crack is observed in the edge of the interface of some specimens

which is caused by the maximum shear stress on the interface. Thus

the sliding failure of the interface is prone to happen. The induced failures of the interface and the interlayer lead to a decrease in tightness of salt rock with an interlayer.