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If Rock is encountered while staking a CSB, can the length of the stake be reduced?  The contractor is recommending 18” min depth per attached.  This would be only in the rock location until full depth can be achieved.  Thoughts?   See our standard drawing for additional stake details.   Thanks for the help!

We have some general thoughts on the proposed modification.

1. First, we should note that the steel pin asphalt tie-down is currently only approved for NCHRP 350. It was successfully evaluated under NCHRP 350, but MASH evaluation has proved more difficult due to wheel snag at the PCB joints that has created excessive occupant compartment deformations. We are currently working on a retrofit to mitigate those issues in the Midwest Pooled Fund.
2. The standard pin configuration provide 32” of pin embedment through the asphalt and road base. Your proposed modification would reduce that embedment 14”. This would provide about 56% of the tested embedment.
3. We do not have a accurate method to determine the change in behavior due to the reduced pin embedment. We believe that the reduced embedment would create larger deflections of the barrier in the region using reduced embedment. However, we anticipate that the pins would still provide significant barrier restraint. Thus, it may be viable to utilize the shorter pins in this installation for a special case and limited use as you described. Additionally, your installation has 14" asphalt depth which should aid the resistance forces on the pins.
4. The case to use the shorter embedment can be supported due to the reduced speeds and impact angles anticipated in most work zones as compared to general highway conditions and the MASH test conditions. Thus, if KDOT is using reduced speeds in the work zone and space is constrained, one can argue that the reduced pin embedment has an increased potential to perform adequately.
5. We would recommend limiting this type of installation to only those areas where rock prohibits full pin embedment.

Please let me know if you have comments or questions.