Investigating the influence of block rotation and shape on the impact process

Abstract

A block impact model based on the elasto-viscoplastic macro element approach is developed for regular base prismatic blocks. This model upgrades a previously conceived model for spherical boulders introducing (i) a rotational degree of freedom; (ii) a moment-rotation relationship; (iii) a toppling mechanism. The model can improve rockfall simulations by considering block geometry and the exchange between translational and rotational energies. Model parameters were calibrated by using laboratory tests on vertical impacts. Parametric analyses were carried out to investigate for both vertical and inclined impacts, the effects of block shape and orientation. The influence of these factors on the impact force, the maximum penetration depth as well as the exchange between translational and rotational energies is discussed. A comparison with the available results for small and large scale laboratory tests shows model capabilities and put in evidence the “nonlinear” relationship between maximum acceleration (or equivalently the maximum contact force) and impact translational velocity. For vertical impacts the trend of the maximum penetration depth is a function of the block shape. Prismatic blocks can experience larger values of maximum penetration than spherical blocks characterized by coincident masses and kinetic energies. In case of bouncing of a prismatic block the increment of normal maximum displacement with respect to spherical blocks ranges from about 66% for triangular base prisms to 132% for hexagonal base blocks. In case of no bouncing, the increments range from about 82% for triangular blocks to −32% for hexagonal blocks. Maximum normal forces also depend on block shape and orientation. In case of a vertex impact with no bouncing, triangular blocks show a decrement in the maximum force of about 43% with respect to the spherical block. The increment of initial block angular velocity generates a reduction in both maximum penetration depths and impact forces.