The mechanism of rockfall disaster: A case study from Badouzih, Keelung, in northern Taiwan

• Combining process-based and empirical-based method to point out unsafe road sections.
• Historical rockfall cases are collected and analyzed for the disaster mitigation.
• 7 critical sections are simulated to understand the characteristics of rockfall.
• Analysis results of rockfall path can provide suggestions for remedial works.

On August 31st, 2013, high intensity rainfall caused a severe rockfall disaster in Badouzih, Keelung. This study combines the results of detailed field investigation and process-based as well as empirical-based method to point out unsafe road sections. The mechanisms and the characteristics of motions of rockfall are analyzed in the field. Two intersecting joints and the bedding plane divided bedrock into blocks. Weathering and the infiltration of rainfall accelerated the erosion process and precipitated ruptures. When the rainfall reached its highest intensity which is 94.5 mm/h in this event, a great deal of water on the slope surface eroded the matrix, causing instability and leading to the failure of the rock blocks. The process of rockfall took 23 s and can be divisible into 4 stages including roll, fall, bounce, and roll. Process-based simulations are adopted in this case and several critical road sections to understand the characteristic of movements. With the empirical-based energy line angle analysis, potential road sections which may affect by rockfall are showed and their energy are also estimated for the purpose of mitigating rockfall impact, reducing similar disasters in this area.