Rotation patterns in a chain of blocks with elbowing

• Elbowing induces non-linearity in block rotations • The rotational response of blocks can be non-monotonic • Corner–surface friction reduces the interior zero angle in Case I • Internal blocks do not rotate when end blocks rotate oppositely • First systematic characterization of elbowing-induced block rotation pattern Block elbowing, the process in which rotating blocks push neighbouring blocks apart, plays a critical role in the deformation of blocky rock masses. This mechanism influences both geological evolution and the stability of mining excavations, remaining insufficiently understood yet. A clearer understanding of elbowing is essential for improving rock mass modelling and ensuring the safety of mining operations. To this end, this paper analyses a chain of stiff square blocks connected by springs, each with translational and rotational degrees of freedom. It was found that blocks in between (passive blocks) may rotate in a complex pattern when end blocks are rotated in same direction (Case I): when the clockwise rotating driving blocks reach a certain critical angle, passive blocks start to rotate anticlockwise and, in some cases, even rotate beyond the initial position (the position with zero rotation). We define the angle of the driving block, when the rotation of the passive blocks returns to zero, as the angle of interior zero. The angle of interior zero decreases as the corner-surface friction increases. When the end blocks are rotated in opposite directions (Case II), the internal blocks do not rotate at all. These results provide the systematic characterisation of block rotation patterns governed by block elbowing, highlighting the roles of local contact friction and friction mode switching from surface-surface to corner-surface contact, and advancing the understanding of blocky rock mass deformation.