Rockfall concrete barrier evaluation and design criteria

Rockfall is the movement of rocks down a slope which may be in the form of freefall, bouncing, rolling and sliding based on the characteristics of slopes and nature of rocks. When the rockfalls reach the roadway, they are hazardous to roadway users. Standardized precast concrete barriers (PCB) or cast-in-place (CIP) concrete barriers are commonly used by Ohio Department of Transportation (ODOT) to protect the affected highways against rockfall hazards. Impact tests were conducted on full-scale PCB and CIP concrete barriers to determine the impact resistance of these types of barriers against rockfall. Manufactured or natural rocks of different sizes and shapes were dropped from ranges of drop heights based on the desired impact energy to capture the performance of these barriers under impact loading. Current ODOT standard details were modified to improve the impact resistance of such barriers. The test results indicated that impact energy absorption capacity of the revised barriers can be increased by more than 100% compared to that of the barriers with the current ODOT standard details. The rollout tests were conducted on three different slopes with CIP concrete barriers constructed at the bottom of these slopes. The first slope was made to an inclination of 30 degrees, the second slope with 45 degrees, and the third slope with 55 degrees. The test rocks were dropped on the top of the slope to roll down and impact the concrete barriers constructed along a ditch at the bottom of the slope. The impacting velocities, the trajectories of the rocks while rolling down the slopes and bounce heights were digitally captured with high speed cameras. The results obtained from rockfall simulation programs such as CRSP were validated using the field measurements obtained from these rollout tests. The results indicated that the predictions obtained from rockfall computer simulation programs generally underestimate the bounce heights and velocities, and consequently the energies delivered by the rocks at the impact location.