Rocks with rotating blocks: 1D displacement, rotation and wave propagation

Fragmentation of rocks, e.g. splitting into blocks, is a common occurrence at a range of scales from rock fragmentation caused by rockbursts or blasting to blocky rock mass produced by systems of fractures to rubble-pile asteroids. Common in these diverse objects is the ability of blocks (fragments) to assume relatively independent displacement and/or rotation.

 

Modelling deformation of blocky/fragmented rocks is complicated by the phenomenon of elbowing [1] whereby the rotating block pushes away the neighbouring blocks. The direction of the push can be independent of the direction of block rotation making the problem strongly non-linear (the “absolute value” type non-linearity). In order to investigate elbowing we constructed a simple 1D physical model of a chain of blocks with one translational and one rotational degrees of freedom. It is found that when one block (the initial block) is rotated, the neighbouring blocks may not rotate, only displace, depending on the magnitude of friction and the number of blocks in the chain. A discrete element (3DEC) model of the chain is developed. It shows the conditions of rotation of the blocks and the rotational wave propagation following a pulse rotation of the initial block.

 

• Pasternak, E., Dyskin, A.V., Estrin, Y. (2006) Deformations in transform Faults with rotating crustal blocks. Pure Appl. Geophys. 163 2011–2030.

 

Acknowledgement. The authors are grateful to Dr I. Shufrin and School of Engineering workshop for help with designing and manufacturing of the physical model. EP and AVD acknowledge support from the Australian Research Council through project DP210102224.