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Guardrail for Fill Slope Applications

Question
State	IL
Description Text	Here is a question regarding options for a roadside barrier in a location where there has been an embankment failure and subsequent repair using a soil nail repair procedure. Also, the roadway top width is narrow, such that we would not have 2' of embankment behind the back of guardrail posts. Records show that the soil nails are present at 4.26 to 5.16 feet below ground surface. If we were to use the 9' posts recommended for guardrail (MGS) in this location, the posts would extend about 6 feet below ground surface, and interference with soil nails would be a concern. We are wondering if you are aware of any other alternatives or variations of roadside barrier systems that might be considered? Also, would use of standard length 6' posts, on 3' 1 ½" spacing be considered under all these constraints? I understand that MwRSF prefers the longer posts for more uniform, reliable results, but we would be open to ideas for mitigating this (soil plates?). Terminals for the guardrail could be placed outside the slope repair.

Question

State

Description Text

Here is a question regarding options for a roadside barrier in a location where there has been an embankment failure and subsequent repair using a soil nail repair procedure. Also, the roadway top width is narrow, such that we would not have 2' of embankment behind the back of guardrail posts. Records show that the soil nails are present at 4.26 to 5.16 feet below ground surface. If we were to use the 9' posts recommended for guardrail (MGS) in this location, the posts would extend about 6 feet below ground surface, and interference with soil nails would be a concern.

We are wondering if you are aware of any other alternatives or variations of roadside barrier systems that might be considered?

Also, would use of standard length 6' posts, on 3' 1 ½" spacing be considered under all these constraints? I understand that MwRSF prefers the longer posts for more uniform, reliable results, but we would be open to ideas for mitigating this (soil plates?). Terminals for the guardrail could be placed outside the slope repair.

System Performance Evaluation

System Types
W-beam Guardrails

Applications
End Treatments, Terminals, and Anchorages
Midwest Guardrail Systems (MGS)
Systems Adjacent to Slope

System Features

Date November 3, 2010
Previous Views (26) Favorites (0)

Response
Response (active)	Recall, MwRSF has developed two barrier options for use on 2:1 fill slopes. Below, you noted the MGS option which utilizes 9-ft long steel posts spaced on 6 ft " 3 in. centers. The 31-in. tall, MGS option was developed under the MASH safety performance criteria. The maximum dynamic deflection was found to be approximately 58 in. Several years ago, MwRSF also developed a metric-height, W-beam guardrail system for 2:1 fill slopes using 7-ft long steel posts spaced on 3 ft " 1½ in. centers. This 27¾-in. tall, W-beam guardrail option was developed under the NCHRP Report No. 350 safety performance criteria. The maximum dynamic deflection was found to be approximately 32 in. Based on the successful performance of the MGS system with 9-ft long posts in conjunction with 58 in. of dynamic deflection, it would seem reasonable that the metric-height system could raised to a 31-in. height and converted to a MGS system. With this modification, the post embedment depth would be reduced by only 3¼ in. from that used for the noted development and crash testing program. In addition, the maximum dynamic barrier deflection would likely fall between 32 and 58 in. With 7-ft long posts, the embedment depth would be 52 in. or 4.33 ft. Based on the information noted above, it is my opinion that MGS should perform in an acceptable manner when installed at the SBP of 2:1 fill slopes if configured with 7-ft long steel posts spaced on 3 ft " 1½ in. centers. If necessary, it would seem reasonable to also construct the MGS at the 32-in. upper height tolerance using 7-ft long posts. With this variation, the post embedment depth would be 4.25 ft.

Response

Response
(active)

Recall, MwRSF has developed two barrier options for use on 2:1 fill slopes. Below, you noted the MGS option which utilizes 9-ft long steel posts spaced on 6 ft " 3 in. centers. The 31-in. tall, MGS option was developed under the MASH safety performance criteria. The maximum dynamic deflection was found to be approximately 58 in.

Several years ago, MwRSF also developed a metric-height, W-beam guardrail system for 2:1 fill slopes using 7-ft long steel posts spaced on 3 ft " 1½ in. centers. This 27¾-in. tall, W-beam guardrail option was developed under the NCHRP Report No. 350 safety performance criteria. The maximum dynamic deflection was found to be approximately 32 in.

Based on the successful performance of the MGS system with 9-ft long posts in conjunction with 58 in. of dynamic deflection, it would seem reasonable that the metric-height system could raised to a 31-in. height and converted to a MGS system. With this modification, the post embedment depth would be reduced by only 3¼ in. from that used for the noted development and crash testing program. In addition, the maximum dynamic barrier deflection would likely fall between 32 and 58 in. With 7-ft long posts, the embedment depth would be 52 in. or 4.33 ft.

Based on the information noted above, it is my opinion that MGS should perform in an acceptable manner when installed at the SBP of 2:1 fill slopes if configured with 7-ft long steel posts spaced on 3 ft " 1½ in. centers. If necessary, it would seem reasonable to also construct the MGS at the 32-in. upper height tolerance using 7-ft long posts. With this variation, the post embedment depth would be 4.25 ft.

Date November 3, 2010
Previous Views (26) Favorites (0)