External Stability of MSE Wall with Crash/Noise Barrier 1

[ghgeo]

I am evaluating the external stability of a MSE wall. There is a noise wall, mounted on a crash (jersey) barrier with moment slab, that sits on the top of the wall.

The applicable design standard states: “Barriers, constructed over or in line with the front face of the panel shall be designed to resist overturning moments by their own mass. Base slabs shall not have any transverse joints, except construction joints. The horizontal loads shall be deemed to be transferred by horizontal shear stress to the reinforced mass and distributed to the upper row of reinforcement only. The upper row of soil reinforcement shall be sized to resist an additional load of 30 kN per linear meter {2 kips per linear foot} of wall. The full reinforcement length shall be considered effective in resisting the impact horizontal load.”

There is a disagreement among my colleges on how to interpret this. Do we need to include wind and crash loads associated with the noise/crash barrier in the external stability analysis of the MSE wall? If yes, how would you calculate the moment arm associated with the loads … i.e., for wind load acting on noise barrier, would the moment arm be equal to the height to of the MSE wall + half the height of the noise wall? Or, are these loads resisted internally and not included in the external stability analysis.

Any insight, suggested references, would be greatly appreciated.

 

[BigH]

My initial reaction is that they are talking only of the stability of the barrier wall. They have added comments on additional design measures for the internal stability. I would suggest that the loading of the barrier wall would be considered a transient load and due to the dead load of the embankment/soil itself should have very little effect on the overall stability - which is considered usually as "behind" the reinforced mass (gravity mass).

 

[mdhshanwil]

These loads are typically applied only for internal design of the MSEW. Your wall designer (assume you're only checking global - that's what it sounds like) will (OK, should) design the structure itself to meet internal stability design requirements. Have never seen these loads applied in global (external) analyses. Although it is an interesting question - some portion of live load is typically applied (per AASHTO) to MSEWs in global analyses when the MSEW acts as an abutment, or supports an approach slab.

 

[Boondog]

External stability is performed for the barrier and counter balance slab design and then the dymamic impact loads are then analyzed for internal stability of the MSE wall. The FHWA design manual illustrates this in example 6.

http://www.fhwa.dot.gov/engineering/geotech/pubs/nhi10024/nhi10024.pdf

 

[ghgeo]

Thanks Boondog! Hadn't realized the new FHWA Manual was available for free download. This will help.

 

[Boondog]

Not a problem.