*2.1. Influencing Factors for the Seismic Deterioration of Contact Interface*

The deterioration effect of seismic action on the contact interface is a complex, dynamically changing process, and the deterioration degree can be quantitatively described by the vibration deterioration coefficient *D<sup>t</sup>* (where *t* is the time). Summarizing previous research results [20–22], it is found that the influences of dynamic cyclic action on the shear properties of the structural plane mainly include the factors of relative velocity and vibration wear. This paper adopts the influence coefficient of relative velocity *γ<sup>t</sup>* and the influence coefficient of vibration wear *η<sup>t</sup>* to quantitatively describe the influences of relative velocity and cyclic action on the ultimate bearing load of the contact interface. Assuming that the relative velocity and the vibration wear are two independent factors throughout the whole duration of the earthquake process, the vibration deterioration coefficient can be expressed as

$$D^t = \gamma^t \eta^t \tag{1}$$
