Based on the theory of single-phase elastic media and unsaturated porous media, the vibration isolation effect of double-layer wave impeding block (WIB) in the unsaturated soil foundation is investigated. Using the Fourier transform and Helmholtz vector decomposition, the calculation formula of the dynamic response of unsaturated ground subjected to a strip harmonic load on the ground surface is established. By analyzing the wave impedance ratio at the interface between the double-layer WIB and the unsaturated soil foundation on the vibration isolation effect of the double-layer WIB, the corresponding interlayer wave impedance ratio of the double-layer WIB with the best vibration isolation effect is selected. On this basis, the influence of load frequency, saturation, thickness, and embedded depth on the vibration isolation performance of the double-layer WIB is analyzed. The results show that the best vibration isolation effect of the double-layer WIB can be obtained by designing the wave impedance ratio at the intersection between the layers of the double-layer WIB. At the same thickness, the vibration isolation effect of the double-layer WIB is better than that of the homogeneous WIB. The double-layer WIB enhances the frequency width of homogeneous WIB vibration damping, which has a better vibration isolation effect on low-frequency, medium-frequency and high-frequency vibration (5 Hz < f < 70 Hz). When the thickness of double-layer WIB exceeds the critical thickness, the vibration isolation effect decreases with the increase in thickness. Soil saturation has a significant effect on the vibration isolation effect of the double-layer WIB, and the double-layer WIB can achieve a better vibration isolation effect at high saturation.
