Abstract:

The time variation characteristic of impact parameters in the contact process between rockfall and slope or protective structure is an important index to describe the process of rockfall collision. It is significant to reveal the interaction mechanism between rockfall and slope and to take reasonable protective measures. In the existing relevant design specifications, there are no calculation methods for the time history relationship of rockfall impact, and only a maximum value of rockfall impact force is determined by referring to relevant specifications or empirical methods. Therefore, based on the linear viscoelastic contact theory, a mechanical model of rockfall impact on the ground is established firstly; according to the different combined initial conditions, two theoretical analytical solutions of the characteristic parameters of rockfall impact are derived respectively. Then, based on the ANSYS/LS-DYNA nonlinear dynamics software, a three-dimensional numerical model is established, and the mechanical characteristics of the rockfalls impacting the ground at different speeds are studied. Finally, the theoretical results of this paper are compared with the indoor test and existing research results, and the following conclusions are drawn: 1) According to the Hertz elastic contact theory, the changes of various parameters show a symmetrical trend during the loading stage and the recovery stage. The characteristic parameters of rockfall impact under the initial condition combination of velocity-acceleration in this paper are very close to the dynamic finite element method, and the initial condition combination of displacement-velocity is not suitable for research on dynamic characteristics under the impact of rockfall. 2) At different speeds and falling heights, the maximum impact force value of the rockfall increases with the increase of the falling height and impact velocity of the rockfall, while the impact time of the rockfall decreases with the increase of the falling height and impact velocity. 3) The maximum impact force and impact time of the rockfall obtained by the calculation in this paper are close to the indoor test and the existing results. Compared with the oscillation of the indoor test and the finite element results, the results of this paper can better reflect the change law of the impact force of the rockfall.          4) Comparing the maximum impact force of rockfall obtained by different methods under a variety of impact speeds, the calculation results in this paper are all within the range of various impact force calculation results, and have good reliability. The results of this paper enrich the rockfall collision theory, which can guide the protection design of engineering related to rockfall disasters.

Key words: rockfall, collision, contact theory, impact force, theoretical analysis