Rotational waves in fragmented and blocky geomaterials

An important mechanism of oscillation and wave propagation in fragmented and blocky geomaterials such as rock masses and the Earth’s crust is the movement and rotation of the fragments/blocks as rigid bodies with deformation mainly residing at the interfaces. There are cases when the gouge in the interfaces is very weak and soft such that the resistance to parting the fragments is provided by the ambient compression which prevents the fragments/blocks from parting but allows their mutual rotation.

 

In order to investigate this type of block movement we performed a series of vibration tests on blocky beams of different heights under horizontal vibrations of the base. The fragmented/blocky geomaterial was modelled using osteomorphic blocks. The osteomorphic blocks have a special shape that ensures topological interlocking. The assembly is an engineered material with internal architecture which captures the fragmented and blocky nature of geomaterials [1]. The observations using the DIC technique confirm that the blocks undergo relative rotational movement. The associated rotational waves travel within the assembly transferring the energy within the blocks. This is an extension of our previous analysis that established the formation of stationary points in fragmented bodies [2]. There is energy exchange between the assembly and the loading device. The energy calculations show that the energy fluctuates around a constant value. The spectrum of block oscillations exhibits the main peak corresponding to the driving frequency as well as secondary peaks that correspond to the multiples of the driving frequency. This is in line with our previous results on bilinear oscillators [3]. The results contribute to the understanding of wave propagation in blocky/fragmented rock mass and the Earth’s crust.

 

1. Pasternak, E., A.V. Dyskin and Y. Estrin, 2006. Deformations in transform faults with rotating crustal blocks. PAGEOPH, 163, 2011-2030.
2. Dyskin, A.V., E. Pasternak and I. Shufrin, 2014. Structure of resonances and formation of stationary points in symmetrical chains of bilinear oscillators. Journal of Sound and Vibration 333, 6590–6606.
3. Dyskin, A.V., E. Pasternak and E. Pelinovsky, 2012. Periodic motions and resonances of impact oscillators. Journal of Sound and Vibration 331(12) 2856-2873. ISBN/ISSN 0022-460X, 04/06/2012.

 

Acknowledgements. The authors acknowledge support from the Australian Research Council through project DP190103260. The authors acknowledge the UWA workshop in developing and manufacturing the experimental setup. In the experiments some setup fixtures previously developed by M. Khudyakov were used. AVD acknowledges the support from the School of Civil and Transportation, Faculty of Engineering, Beijing University of Civil Engineering and Architecture.