Experiment on the effect of forward and reverse rotation speeds of rockfall on normal restitution coefficient
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摘要:
为探究落石正转和反转转速对法向恢复系数（Rn）的影响，选制正方、圆盘和圆柱三种典型形状试块，通过专门研发的落石碰撞测试装置，开展不同正转和反转转速下试块绕X和Y轴与坡面的碰撞测试。试验结果表明：圆盘和圆柱状试块绕Y轴旋转时（近似正碰），转速对Rn基本无影响；3种形状试块绕X轴旋转时（非正碰），转速和Rn存在一定相关性，但Rn还受到试块形状和冲击姿态联合影响。为此，引入综合变量-冲击姿态系数（IPC）来量化转速对Rn的影响。鉴于不同冲击姿态下法向冲击力对Rn的力学作用机制存在差异，对试块冲击回弹特征采取分类探讨。一次冲击回弹型，正转试验中质心（C）在接触点（CP）之后和C在CP之前条件下，IPC与Rn分别呈线性正相关和负相关关系；反转试验结果则正好相反。二次冲击回弹型，无论正转或反转，第一次冲击C在CP之前或之后，各形状试块IPC与Rn均为强正相关，但各工况下的相关规律并不一致。这些获得的结论基本揭示了转速对Rn的影响关系，同时为转动异形落石冲击回弹过程的精准预测提供了参考。
Abstract:In order to explore the effect of forward and reverse rotation speeds of rockfall on normal restitution coefficient (Rn), 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 Rn 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 Rn, but Rn 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 Rn. In view of the difference of the mechanical action mechanism of normal impact force on Rn 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 Rn 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, Rn 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 Rn, and provide a reference for accurate prediction of impact-rebound process of rotating irregular rockfall.
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Key words:
- forward rotation /
- reverse rotation /
- restitution coefficient /
- impact posture coefficient /
- rockfall
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表 1 试块与坡面特征参数及试验初始条件
Table 1. The characteristic parameters of the block and slope and the initial conditions of the test
试块特征 岩石类型 形状 尺寸 V/（m∙s−1) α/(°) 初始转速/
(r∙min−1)特征长度 值/mm 灰岩 正方体 边长 40.3 3.5 40 100~500
（正/反转）圆盘 直径/厚度 58.6/24.3 圆柱 直径/高 33.78/73 坡面特征 岩石类型 形状 尺寸 特征长度 值/mm 灰岩 长方体 长/宽/高 700/500/150 
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