Model tests on anomalous low friction and pendulum-type wave phenomena

• Published in: Progress in natural science 2009-12, Vol.19 (12), p.1805-1820
• Main Authors: Wu, Hao, Fang, Qin, Lu, Yusheng, Zhang, Yadong, Liu, Jinchun
• Format: Article
• Language: English
• Subjects: Anomalous low friction; Block-hierarchical structure; Canonical sequence; Deep-block rock mass; Pendulum-type wave
• ISSN: 1002-0071
• DOI: 10.1016/j.pnsc.2009.09.001

The anomalous low friction （ALF） and pendulum-type wave （μ wave） phenomena were two typical, nonlinear, geo-mechanical, and dynamic responses in deep-block rock mass discovered from in situ observations, which occurred from the movement of the geo-blocks under the impact of external pulses, such as deep confined explosion, earthquake, and rock bursts. With the aim to confirm the existence of the above two phenomena and study the variation laws of them experimentally, laboratory tests on the granite and cement mortar continuum and blocks models were conducted on the self-independently developed multipurpose testing system, respectively. The ALF phenomenon was realized under two loading schemes, the blocks model and working block were acted upon by the joint action of vertical impact and horizontal static force as well as the joint action of both vertical and horizontal impacts with different time intervals. It revealed that the discrete time delays corresponding to the local maximums and minimums of the horizontal displacement amplitudes and residual horizontal displacements of the working block satisfied the canonical sequences with the multiple of √2, most of which satisfied the quantitative expression （√2）Δ/Vp. Besides, the one-dimensional impact experiments were carried out on the blocks granite model, continuum, and blocks cement mortar models, respectively. Based on the comparison and analysis of the propagation properties （amplitudes and the Fourier spectrums of acceleration time histories of blocks） of the 1D stress wave in the above models, it is indicated that the fractures in rock mass have tremendous effect on the attenuation of acceleration amplitudes and high-frequency waves. By comparison of the model test data with the in situ measurement conclusions, the existence of the μ wave was confirmed experimentally in the cement mortar blocks model with larger dimensions, and the frequencies corresponding to the local maximums of spectral density curves of three-directional acceleration time histories of sub-blocks also satisfied several canonical sequences with the multiple of √2.