关键词: 边坡工程, 带状震源, 破裂机制, 斜坡动力响应, 离散元数值模拟

Abstract: According to the realistic damage characteristics of slopes on the seismogenic faults as well as the fracture mechanismss of the faults in the Wenchuan earthquake, a so-called strip-shape hypocenter is employed to assess the dynamic responses of the typical slopes. Furthermore, the strip-shape hypocenter can be divided into four stages in accordance with their spatial locations from the initial break to the end break of the seismogenic fault. These stages consist of the thrust fault hypocenter, the thrust and a bit strike-slip fault hypocenter, the thrust and strike-slip fault hypocenter and the strike-slip and a bit thrust fault hypocenter. Thus, the distinct element method is applied to simulate the dynamic response of the Daguangbao landslide on the Longmenshan seismogenic fault in Sichuan province in China. Then, the dynamic formation mechanism, the triggered main controlling factors, and dynamic characteristics of damage, collapse and accumulation are revealed. The results show that the critical damage of the slope is mainly caused by the thrust and a bit strike-slip fault hypocenter, by considering the location of the front end of the fault break and the formation time of the critical damage. While before the critical damage of the slope, its damage is induced by the thrust fault hypocenter between the initial break of the faults and Wenchuan county. The following processes of ejecting, colliding, crushing and accumulating are mainly triggered by the coupled inertia force and the gravitational force, which are also influenced at a certain degree by the above two kinds of hypocenters with respect to their fracture mechanisms. Before the critical damage, the whole slope underwent a positive horizontal distance towards its free face. Then, the slide bed begins a negative horizontal distance away from its free face with a continuous positive horizontal distance of the slide mass, which results in a critical separation between them. At the ejecting, colliding and crushing stage, the slide bed continues its negative horizontal displacement to an extreme limit, then a positive horizontal one and followed by its zero horizontal displacement. The vertical displacement at this stage is relatively small. The motion characteristics of the slide bed in this process is in accordance with that of the monitoring seismic data, for example, the acceleration, the velocity and the displacement. Meanwhile, the slide mass continues its positive displacement to a constant limit with a colliding, crushing, accumulating to self-stabilization process. As far as the mechanical factors are concerned, the horizontal seismic force formed by the single thrust fault hypocenter and the thrust and a bit strike-slip fault hypocenter provides a key contribution to the whole slope including the slide bed and the slide mass before the critical damage state. At the ejecting, colliding, crushing and accumulating stage, the dynamic responses of the slide mass is mainly influenced by the inertia force and the gravitational force. However, on the basis of a special topography, the horizontal and the vertical seismic forces from the following two hypocenters give their finite influences to the slide mass.

Key words: slope engineering, a strip shape hypocenter, fracture mechanism, slope dynamic response, distinct element numerical modeling