Impact of rock block characteristics on rockfall hazard and its implications for rockfall protection strategies along Himalayan highways: a case study

Rock block characteristics are the controlling factors that define the potential rockfall volume, associated hazard and design of preventive practices. The present study defines a methodology to demonstrate the impact of block characteristics on rockfall hazard and its implications on the design of mitigative measures by analysing a recurring rockfall site along a critical highway corridor in NW Himalaya, India. The field data were quantitatively characterised for statistical distributions of size and volume of in situ as well as rockfall blocks. Possible block failures and rockfall initiation zones were predicted using modified kinematic analysis and distinct element method. The size and volume distributions as well as shapes were simulated against these predicted initiation zones to determine the cumulative impact of block characteristics on rockfall hazard by analysing the block kinetics and trajectories. It is found that the block initiation zones majorly govern the relative bounce height, kinetic energy, run-out distance and impact down the slope respective of block sizes and associated mass coupled with slope geometry. However, the effect of block shapes is observed to be minor compared to the blocks greater than a particular size range. Therefore, the design of rockfall protection such as barrier can be more effective when considering the kinetic energies of such block size range assisted by initiation zones. This study proposed that the knowledge of block size frequencies and rockfall initiation zones could provide a rational threshold for which a protection strategy can be designed and optimised to prevent rockfall hazard along the Himalayan highway corridors.