We have a requirement to anchor the temporary concrete barrier if is closer than a specified distance to a 2-foot or greater dropoff. A question has come up on how to define the maximum steepness of dropoff. What is the maximum steepness of dropoff slope that wouldn't require anchoring?
Could an impacting vehicle penetrate or vault the barrier as a result of a barrier deflecting beyond the edge of a dropoff?
The through-bolt tie-down system provided in TRP-03-134-03 was designed, tested, and evaluated for use with barrier placement on rigid concrete pavement adjacent to a vertical drop off. For this 2000P test, part of a barrier was pushed back slightly, thus extending over the drop off edge but without concern. Certainly, this same barrier and tie-down system could be used at similar locations where shallower roadside slopes exist.
Now, if you do not want to use the tie-down system near drop-offs and roadside slopes, it would be necessary to provide level pavement, or nearly level pavement (say 10:1/12:1 or flatter), on the back side of the barrier. These conditions would allow the impacted barrier to deflect backward without dropping over an edge or slope break point. If a free-standing barrier drops over an edge or modest roadside slope, then there exists and increased propensity for vehicle climb up the barrier, vaulting, and rollover. If a barrier is positioned on soil, then the barrier can sink into the soil. Then, when it is impacted, it may actually dig into the soil and result in increased barrier rotation and vehicle climb, vaulting, and rollover.
In summary, anchoring a TCB to a rigid pavement would not be required as long as you provide adequate space for barrier deflection on a level surface during impact events. For such a situation, a vertical drop-off could be accommodated beyond that distance.
Thanks for the opportunity to review the proposed hazard mitigation design. From my review of the attached discussion and details, I assume that the authors are planning to allow impacting vehicles to travel up and over the sloped berm and onto the top of a single-slope concrete median barrier. This action would result in vehicles rolling off of the top of the barrier or traveling forward and entering the separated median barrier and bridge pier region. Second, angled impacts near the nose of the berm but slightly down the side could result in the vehicle being tripped and launched over the barrier system, potentially rolling over as well. As such, I do not recommend that the Ohio DOT nor any municipality use the sloped berm concept described below to treat the tall, single-slope concrete median barrier. Please feel free to discuss this matter with me at your convenience!