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I received the following email from one of our designers (see below).  I have included my initial response back to the designer in the attached word document.  If MwRSF could provide additional guidance on this topic to me, it would be greatly appreciated.

-----Original Message-----

 Hello-

 The subject project is a 3R resurfacing project with 7 intersection

 realignments.  The typical is 12' lanes with 6' shoulders (3' paved). 

 The project is at about a 60% level right now.

 The question I have is regarding the use of longer beam guard posts

 and the use of "Beam Guard Retaining Walls".  The PDF is a scan of the

 detail sheet and Misc Quant sheet from the 1988 As-Built, when the

 project was last resurfaced.

 The current project is milling 1.5" of HMA and paving 4.25"-5.25",

 making the new vertical profile of STH 144 @ 2.75" to 3.75" higher than existing.

 All of the existing beam guard is being replaced.  With the additional

 shoulder gravel that will be required due to the profile change, I

 foresee problems with erosion at shoulders in the beam guard areas. 

 Either asphaltic curb and flumes will need to be installed under the

 beam guard to control the erosion, or the foreslopes will have to be

 paved.  Do you have any recommendations on this?

 Also, the existing foreslopes are very steep (and long), and many of

 the existing posts are installed down the foreslope a foot or more. 

 In other words, the face of beam guard was installed at or near the

 shoulder grade break.  This is apparently why 8' or even 12' posts

 were specified in some locations on the 1988 As-Built - so the posts

 were embedded enough to develop full strength.  The "Retaining Walls"

 were used to help prop up the shoulders near areas of culverts/box

 culverts/cattle passes where there was no room to build up the shoulders.

 Due to the nature of this project, we would like to avoid having to

 fill in the slopes.  A lot of earthwork would be required to fatten

 these slopes because they are so long.  I have heard that other

 regions sometimes use similar details to solve these types of

 problems.  Do you have any ideas for dealing with these problems, or

 any construction details that other regions use?  If not, we may just

 use a modified version of the old detail that was used last time on this project.

 Attached are some pictures of the areas in question.  As you can see,

 many of the posts lean backwards due to the settling of the foreslopes

 over the years.  However,  I believe that the leaning posts were

 installed at the standard 6' length and not the 8' or 12' lengths.

For fill slopes as steep as 2:1, MwRSF researchers have developed two strong-post W-beam guardrail systems for use at the slope break point. The first system utilized metric height W-beam rail (27-3/4" or 706 mm) with 7-ft long, W6x9 steel posts spaced on 3-ft 1-1/2-in. centers. The second system utilized the MGS with a 31-in. top height along with 9-ft long, W6x9 steel posts spaced 6-ft 3-in. on centers. For 2:1 slopes, both guardrail systems can be used. Additional discussion on this topic has been provided in the MGS Implementation discussions that I led last fall. I believe that we also provided recommendations for slopes less than 2:1. I will see if I can provide that here as well.

MwRSF: Recently, the Mn DOT requested guidance for placement of standard and MGS guardrail adjacent to slopes of various configurations. In response to this request and using available crash test data as well as engineering judgment, Dr. Dean Sicking and Mr. Bob Bielenberg prepared the preliminary guidance, subject to refinement in the future. It is as follows:

For standard W-beam guardrail:

1.  Standard W-beam guardrail placed adjacent to any slope with 2' of level soil behind the posts is acceptable.

2.  For w-beam guardrail placed 1'-2' adjacent to a 6:1 or flatter slope, standard 6' W6x9 posts at standard spacing are recommended.

3.  For w-beam guardrail placed 1'-2' adjacent to a 3:1 to 6:1 slope, 7' W6x9 posts at standard spacing are recommended.

4.  For w-beam guardrail placed less than 1' adjacent to a 3:1 or steeper slope, 7' W6x9 posts at half spacing are recommended.

For MGS guardrail:

1.  Standard MGS guardrail placed adjacent to any slope with 2' of level soil behind the posts is acceptable.

2.  For MGS guardrail placed 1'-2' adjacent to a 6:1 or flatter slope, standard 6' W6x9 posts at standard spacing are recommended.

3.  For MGS guardrail placed 1'-2' adjacent to a 3:1 to 6:1 slope, 7' W6x9 posts at standard spacing are recommended.

4.  For MGS guardrail placed less than 1' adjacent to a 3:1 or steeper slope, 9' W6x9 posts at standard spacing are recommended.

In the photographs and design details that you provided, discrete W-beam rail segments were shown bolted to the face of guardrail posts both above and below grade and for retaining soil. We do not believe that this practice should be used. In addition, when asphalt overlays are placed in advance of the guardrail without placing new fill behind the posts, the post-soil behavior is altered. An even greater concern is whether the long, wood posts can rotate at the appropriate load without fracturing. In the past, we have developed recommendations for such cases for the Missouri DOT and with using steel posts. This recommendation was based on the best available data and engineering judgment - no testing. I can find that recommendation if you desire it.

In several of your photographs, the guardrail posts are tipped backward. If subsequent work were to occur in these areas, it would be suggested that the guardrail systems be adapted to meet those noted above and that the posts be placed vertical to reduce any tendencies for vehicle climb and override.

Other photographs also reveal the use of buried, turned down end terminals that are not in a back-slope. If modifications are to occur to these guardrail systems, you will need to review the WsDOT policies for replacing these terminals when certain 3R or roadway surfacing activities are scheduled. I assume that WsDOT has a policy on when guardrail terminal upgrades are to occur. Once again, it is highly recommended that you review this policy before doing any work around these terminals to ensure that you follow your long-range implementation plan for certain roadway classifications.