Precast Sound Barrier Wall Load Paths?

[kyjocro]

I recently worked on the consulting side of a DOT Sound Barrier Wall project. Typically the objective of these projects is to tell the designers if the soils meet the standard specs for their (DOT) pre-engineering structural designs (N=X, Phi>X Gamma'>XX.X pcf). If not, provide Geotechnical parameters, etc. The walls are founded on Auger Cast Piles (ACP) and the walls are precast panels that are slipped between the posts.

My question is basically trying to figure out the load transfer mechanism for this type of structure. Do the wall panels transfer all of their vertical loads to the piles or does the ground soil provide vertical reactions as the pile settles over time? I computed pile capacities based on skin friction/bearing capacity design methodologies for bored concrete piles vs. calculated dead loads(assuming self weights based on geometries) and the allowable pile capacities (based on standard designs) were not enough for the dead load.

Does anyone have any insight/experience on how these structures transfer load to the foundation?

I realize this may be a STRUCTURAL question, but I figured I'd start here and get any GEOTECH insight available since it is also a foundations question.

Thanks in advance,
kyjocro

 

[MiketheEngineer]

I thin there are brackets in the piles that "stop" the walls from sinking to China.

Check the mfg drawings

 

[kyjocro]

Hey Mike,

Thanks for the reply. I have checked all the drawings that I could come by and don't see any note or geometry indicating brackets on the piles. Are you thinking of Helical Piles maybe?

-kyjocro

 

[Ron]

Assume the piles take the entire load of the walls. Since there are presumably no grade beams between the piles, then soil strains and pile strains under the same load at the surface are incompatible, so the pile "wins".

 

[kyjocro]

Thanks Ron. That's what I assumed was the scenario. I guess I just need to triple check my calcs.

 

[apsix]

I would look at using Safety Factors on the low side, as the consequence of some minor settlement is low.

 

[hokie66]

I am surprised that the dead load of the panels creates a problem for any competent pile. It seems to me that overturning due to wind (or perhaps earthquake) loading would control.

 

[fattdad]

Overturning from wind load is the big factor. We (VDOT) always procure sound walls using design-build, just providing the geotechnical data (i.e., subsurface exploration, N-values, classification testing) for the D-B'rs use.

f-d

¡papá gordo ain’t no madre flaca!

 

[Ron]

Agree with hokie66 and F-D. Vertical load on the piles is the least of your issues; however, the vertical load will be taken by the piles, not the direct soil interface. Moment at the post/Augercast pile interface will be quite high if you have any reasonable wind load.

 

[Riggly]

Kyjcro, I know I am late on this, but I do agree with FD and hokie. In a situation like that, you have to consider the stiffness ratio. That is the stiffness of the soil to the ACP. Even if the panels are resting touching the ground, most of the load will mostly be transfered to the stiffer element in the group. So conservatively, I would typically assume that all the load will be transferred to the piles.

Stiffness ratio is an important concept that is often over-looked.