Experiment on the effect of forward and reverse rotation speeds of rockfall on normal restitution coefficient

In order to explore the effect of forward and reverse rotation speeds of rockfall on normal restitution coefficient (R_n), three typical blocks of cube, disc and cylinder were customized, and the impact tests of each block with slope at different forward and reverse rotation speeds in X and Y axes were carried out through the specially developed rockfall impact test device. Results show that the rotation speed has no effect on R_n when the disc and the cylinder shaped blocks rotate around the Y-axis (approximately normal impact); when the three shaped blocks rotate along the X-axis (non-normal impact), there exists a certain correlation between the rotation speed and R_n, but R_n is also affected by the block shape and impact posture. Thus, a comprehensive variable - impact posture coefficient (IPC) was introduced to quantify the effect of rotation speed on R_n. In view of the difference of the mechanical action mechanism of normal impact force on R_n under different impact posture, the impact-rebound characteristics of the blocks were classified and discussed. For the type of rebounding after only one impact, IPC and R_n have linear positive correlation and negative correlation respectively when the mass center (C) is behind and in front of the contact point (CP) in the forward rotation test, and the results of the reverse rotation test were just the opposite. For the type of rebounding after two impacts, regardless of forward or reverse, whether C is behind or in front of CP during the first impact, R_n and IPC of each shaped block are strongly positive correlation, yet the relevant laws are not consistent under various working conditions. These conclusions basically reveal the influence of rotation speed on R_n, and provide a reference for accurate prediction of impact-rebound process of rotating irregular rockfall.