Review and prospects of propagation characteristics of pendulum-type waves in blocky rock masses

Rock masses have complex hierarchical structures, and the deformation of rock masses under both static and dynamic conditions is primarily concentrated at weak structural layers, which provides the possibility for the whole translation and rotation of rock blocks, and may induce a new type of nonlinear-alternating displacement waves that are completely different from traditional seismic waves, namely the pendulum-type waves (including longitudinal and transverse pendulum-type waves) and rotational waves. Pendulum-type waves have the characteristics of low frequency, low velocity, large amplitude and high energy, which can cause strong compression and anomalously low friction effect in weak layers of rock masses, and may lead to overall instability and lateral sliding of the roadway structure, thereby inducing the rockburst disasters. At present, the study of pendulum-type waves has obtained many achievements and is gradually being applied in engineering, but there are still many problems to be solved. Therefore, it is necessary to systematically review and summarize the pendulum-type wave phenomenon in blocky rock masses. Firstly, a systematic summary of domestic and foreign research achievements related to the pendulum-type waves is conducted, and the discovery, verification, on-site tests, laboratory tests, theoretical modeling and application of pendulum-type waves are briefly described. Secondly, the research achievements of the author's team in the field of pendulum-type waves in recent years are briefly introduced. Through theoretical analysis and experimental research, the propagation laws and typical characteristics of pendulum-type waves in 1D and 2D blocky rock masses have been thoroughly studied, and the influence of hierarchical structures on pendulum-type wave propagation in blocky rock masses is determined. Furthermore, the application of pendulum-type wave theory in anti-impact support of roadway is analyzed, and the mechanism of low-frequency and low-velocity characteristics, rock rotation and the disaster induced by pendulum-type waves are revealed. Finally, the future research focus and development trend of pendulum-type waves in blocky rock masses are prospected, which can provide reference for related researchers.