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blocked MGS in front of a retaining wall

State WI
Description Text We have a project where there is a need for a retaining wall behind a beam guard. The beam guard is preventing vehciles from droping off the retaining wall. I was asked how close can the retaining wall be to the blocked MGS without interfearing with the post rotation and providing adequate soil mass to absorb impact.
  • Guardrail
Other Keywords retaining wall
Date May 10, 2013


Definitive research into minimum MGS guardrail offsets from MSE or retaining walls has not been conducted at this time. Previous research regarding MGS guardrail placed adjacent to a wire-faced MSE or gabion wall was conducted at MwRSF. Our final recommendations included a minimum lateral placement from outer edge of 4 ft 9 in. based on post embedment 1 ft away from 3-ft wide wall facing fill (larger stones). However,the construction of your MSE may be much different than used in our R&D effort and may allow for steel posts spaced closer to outer vertical wall edge.

The main concerns with respect to MGS guardrail placement adjacent to MSE or retaining walls is that the post placement doesn't interfere with the MSE wall, that the offset from the back of the post to the wall does not affect the post-soil resistive forces, and that the rotation of the post does not damage the MSE or retaining wall. Based on previous testing of guardrail posts at MwRSF, a 2-ft offset from the back of the post to the inside edge of the retaining wall should be sufficient to alleviate the latter two concerns. Two feet of soil behind the post should provide adequate space for developing the proper post-soil resistive forces and prevent the rotating post from impacting the inside of the retaining wall.

The above offset guidance is valid for level terrain only. If the MGS was installed adjacent to slopes and a retaining wall, further consideration would be needed.

Date May 30, 2013

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