<p>This paper investigates the dynamic behavior of a circular tunnel in multi-layer soil structures under complex boundary conditions. Initially, seismic SH waves acting on these structures are considered. Using the series expansion method, analytical expressions for the scattering waves in each soil layer are derIVed. Subsequently, an analytical expression for the standing wave, satisfying stress-free conditions at the boundaries of a V-shaped canyon, is established using the fractional-Bessel-function-expansion-method and Graf-addition-theorem. Furthermore, the large-arc assumption method is employed to transform straight boundaries into curved ones within the multi-layer soil structures, and expressions for scattering waves due to these curved boundaries are obtained. Integral equations are formulated based on boundary conditions and solved using orthogonal-function-expansion techniques with efficient truncation. The calculation results analyze and discuss the dynamic-stress-concentration-factor of the tunnel within different soil layers. Additionally, the performance of the analytical solutions is validated by comparing them with finite-element-method solutions.</p>