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Driving Posts Through MSE Wall Reinforcement

Question
State	WY
Description Text	Following up on a previous question to the pooled fund regarding AASHTO LRFD requirements for guardrail posts placed in MSE walls dated February 13, 2014. The response referenced report TRP-03-235-11, “Development of an Economical Guardrail System for use on Wire-Faced MSE Walls”. The response also mentioned that the posts should be installed in accordance with AASHTO LRFD 11.10.10.4. In this section, it discussed penetrations through the reinforcement and recommended steel boxes be fabricated around “leave-outs” in the mesh, tying them to the mesh to provide continuity of the reinforcement. This creates many problems including trying to accurately locate these “leave-outs” when installing the posts and it could be very expensive. I am wondering if it is O.K. to drive the posts through the mesh and any material separation fabric. This would create the smallest possible penetration area through the mesh. This would likely only penetrate one to two layers of mesh located at the top of the wall where the lateral soil forces are fairly low anyway. A concern that has been raised is if this could pull the mesh out of position when the posts are driven through it. I noticed in the MwRSF report on gabions (marked “Draft”), it shows that the steel guardrail posts were driven through the wire reinforcement mesh and the material separation fabric. There was not discussion about this however. Did MwRSF experience any problems with this installation? Is this an acceptable way to install the posts by just driving them through the mesh and fabric? We have had our field personnel asking about installing sonotubes and neatly cutting the reinforcement around the tubes. I think this is a bad idea since it would introduce larger “leave-outs” in the mesh and confine soil around the posts making them overly stiff.

Question

State

Description Text

Following up on a previous question to the pooled fund regarding AASHTO LRFD requirements for guardrail posts placed in MSE walls dated February 13, 2014. The response referenced report TRP-03-235-11, “Development of an Economical Guardrail System for use on Wire-Faced MSE Walls”. The response also mentioned that the posts should be installed in accordance with AASHTO LRFD 11.10.10.4. In this section, it discussed penetrations through the reinforcement and recommended steel boxes be fabricated around “leave-outs” in the mesh, tying them to the mesh to provide continuity of the reinforcement. This creates many problems including trying to accurately locate these “leave-outs” when installing the posts and it could be very expensive. I am wondering if it is O.K. to drive the posts through the mesh and any material separation fabric. This would create the smallest possible penetration area through the mesh. This would likely only penetrate one to two layers of mesh located at the top of the wall where the lateral soil forces are fairly low anyway. A concern that has been raised is if this could pull the mesh out of position when the posts are driven through it. I noticed in the MwRSF report on gabions (marked “Draft”), it shows that the steel guardrail posts were driven through the wire reinforcement mesh and the material separation fabric. There was not discussion about this however. Did MwRSF experience any problems with this installation? Is this an acceptable way to install the posts by just driving them through the mesh and fabric? We have had our field personnel asking about installing sonotubes and neatly cutting the reinforcement around the tubes. I think this is a bad idea since it would introduce larger “leave-outs” in the mesh and confine soil around the posts making them overly stiff.

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Date April 2, 2014
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Attachment Q-Driving Post Thru MSE Reinforcement.docx

Response
Response (active)	During the installation (and repair) of the MGS system placed on top of an MSE wall, MwRSF installed the steel posts utilizing a post driver. This most like led to the post tearing through small areas of the top layer of wire-mesh of the MSE wall. Throughout the installation of the system, repairs to the system, and 2 full-scale crash tests, no movement was observed from the MSE wall. Thus, driving the posts through the wire mesh did not appear to have any negative effects. However, please note that this was for steel posts only. As noted in a follow-up report (TRP-03-256-12), further evaluation would be necessary for recommendations concerning driving wood posts through the wire mesh due to the larger cross section area, softer material, and difficulties with removal of damaged/fractured posts. Additionally, without further study, MwRSF would not recommend the use of sonotubes as this will affect a larger area of the MSE wall's wire mesh.

Response

Response
(active)

During the installation (and repair) of the MGS system placed on top of an MSE wall, MwRSF installed the steel posts utilizing a post driver. This most like led to the post tearing through small areas of the top layer of wire-mesh of the MSE wall. Throughout the installation of the system, repairs to the system, and 2 full-scale crash tests, no movement was observed from the MSE wall. Thus, driving the posts through the wire mesh did not appear to have any negative effects. However, please note that this was for steel posts only. As noted in a follow-up report (TRP-03-256-12), further evaluation would be necessary for recommendations concerning driving wood posts through the wire mesh due to the larger cross section area, softer material, and difficulties with removal of damaged/fractured posts. Additionally, without further study, MwRSF would not recommend the use of sonotubes as this will affect a larger area of the MSE wall's wire mesh.

Date April 11, 2014
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