Block Sliding and Rotation Patterns in Panels of Blocks: The Role of Elbowing

Understanding the mechanical behaviour of blocky materials and structures is critical in engineering fields dealing with rock masses, masonry, ice crust, and fault gouge. The diverse block kinematics make mechanical responses difficult to predict. An important mechanism controlling deformation of block assemblies (e.g., blocky rock mass) is so-called block elbowing, a process in which rotating blocks push neighbouring blocks apart. Previously, this mechanism has been studied using 1D chain models; however, the effect of higher dimensionality has not been fully understood. In this paper, a two-dimensional blocky structure (block panel) is analysed. It is found that adding a kinematic degree of freedom fundamentally alters structural behaviour. The rotation angle of blocks remains the same such that the assembly breaks into layers sliding over each other; however, the mutual sliding is complex and dependent on frictional conditions. First, the structure becomes skewed, with the sliding directions both subhorizontal and/or subvertical. Second, the sliding modes are not necessarily purely subhorizontal or purely subvertical; combined sliding patterns are more prevalent. These observations highlight the fundamental role of elbowing in governing the block kinematics. In frictionless conditions, coordinated block rotations and complex block sliding are observed. The only mechanism capable of producing this behaviour is elbowing. In frictional conditions, sliding is considerably restrained and the assembly tends to rotate as a whole. These findings contribute to the understanding that neglecting block elbowing may overlook critical deformation mechanisms. The results provide a mechanical basis for analysing blocky structures in rock engineering and related geophysical systems.