There are often differences in the physical and mechanical properties of slope topography and its constituent rocks in nature. Therefore, under strong seismic conditions, these differences can lead to slopes exhibiting different dynamic response characteristics. In recent years, cross-river large-scale engineering construction has become more and more frequent, and the topography of the river valley has a significant amplification effect on the ground motion, and the appearance of the wave impedance layer increases the sensitivity of the resonance effect of the side slopes, and the joint action of the medium wave impedance ratio n and the topography tends to cause a strong amplification effect on slope surface displacements. In order to deeply analyze the dynamic response law under the change in wave impedance of shallow surface-layer medium in combination with the change in slope gradient of river valley bank, a simplified linear model of river valley was established. In this model, the slope gradient of the left bank is set to be fixed at 45°, while that of the right bank is set to be three different choices, which are 30°, 45° and 60°, and the bank slope medium is divided into two layers, namely the inner part composed of the micro-neophyte rock and the surface layer made up of weathered rock. On this basis, considering the change in wave impedance ratio of the shallow surface layer of the right bank slope, a total of six values of the wave impedance ratio are set as 1, 1.5, 2, 2.5, 3, 3.5.

The dynamic simulation was carried out using the discrete element software UDEC. The plastic principal model was adopted and the Mohr-Coulomb yield criterion was followed. The results show that:

1） The presence of a shallow wave impedance layer on the river valley slope significantly enhances the dynamic response of the slope, and this enhancement effect is especially obvious on the slope surface where the slope height reaches more than one quarter.

2） The slope gradient of the left bank is fixed at 45°, and of the right bank changes. This causes the left bank slope to exhibit different dynamic response characteristics during seismic activity. This difference lies in distinct force conditions and dynamic responses of the side slopes due to the change in slope gradient of the right bank. Furthermore, the asymmetry of the valley morphology has a significant effect on the ground dynamic response of the bank slopes. Compared with the symmetrical valley morphology this asymmetrical feature can enhance the ground dynamic response of the bank slopes, thus affecting the stability and safety of valley slope.

3） When the seismic wave vertically impinges on the valley slope model, the dynamic response of the right bank slope gradient in the heterogeneous model follows the order of 60°＞45°＞30°, which shows that with the increase of the right bank slope gradient, the dynamic response of the slope becomes stronger. When the wave impedance ratio n is in the range of 1.5−2.0, the peak acceleration of the slope increases linearly with the wave impedance ratio n, and when n is greater than 2.0, it shows a nonlinear characteristic. The PGA amplification factor and wave impedance ratio n for the monitoring point 5′ at the top of each model slope are fitted, and the goodness of fit is greater than 0.8, especially the fitting effect of 30° bank slope gradient is the best, suggesting that the relationship between wave impedance ratio n and PGA amplification factor can be effectively quantified under the specific background of considering influencing factors. At the same time, it is found that when the wave impedance ratio n is 2.5, 3, 3.5, the relationship between PGA amplification factor and slope gradient at the monitoring point 5′ on the top of the slope is a linear increasing function.

4） When the seismic wave propagates into the slope model from the left side of the valley, the PGA amplification factor of the left bank is between 1.03 and 4.02, and that of the right bank is between 0.25 and 1.49, showing a significant backslope effect. The dynamic response of the toe of the left bank of the slope is inhibited by the shallow surface wave impedance n.

5） Stress differentiation exists on both sides of the medium interface, and the tensile stress is distributed on the shallow surface of the slope. The tensile stress makes the surface rock structure tend to be unstable, and the PGA amplification factor of the slope surface is significantly larger than that of the slope’s interior. It is not a single condition that leads to the difference in the dynamic response of the valley slope. The combined effects of topographic slope, wave impedance ratio of shallow surface layer and propagation direction of seismic wave result in different in dynamic response of valley slopes.