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We are installing MGS barrier adjacent to a fill section where part of the fill is dumped rock (see attachment).  Can standard MGS barrier be used in this situation at 1' from the break point or are long posts or a reduced post spacing necessary?

Thanks!

The MGS has not been evaluated adjacent to slopes as steep as the 1:1 slopes shown in your detail. Additionally, it is not known how much additional lateral support for the post will be provided by the dumped rock fill as it is not compacted. 

Due to these concerns, it may not be advisable to use the standard 6' MGS post length in this type of installation. The MGS has been successfully tested at the slope break point of to 2:1 slopes with 6' posts, but barrier deflections increased significantly.  

The MGS was also evaluated adjacent to 2:1 slopes with 8' and 9' long posts. These tests had lower deflections and would likely perform better in this installation with a 1' offset to a 1:1 slope. Thus, we would recommend using either 8' or 9' long posts in this type of installation. 

If you desired to keep the 6' post length, we would recommend a minimum offset of 2' from the back of the post to the slope break point. 

Note that none of these specific installations have been full-scale crash tested, adjacent to 1:1 but they represent our best engineering judgement based on the current data for the performance of the MGS adjacent to slopes.