MSE Bridge Abutment Footing Depth

[RichBridge]

I'm looking into preliminary designs using MSE bridge abutments and I have been gathering as much info as I can. I'm looking at using spread footings without piling for the bridge footings that a few feet back from the MSE wall face.

One thing that seems to be a design delimma is that the spread footing for the bridge is only a foot or so below top of soil at the front of the footing. If it were deeper, it would interfere with the MSE wall reinforcing. But because it's only one foot down, it's not nearly deep enough to be below the frost line. At the rear of the footing, it is below the frost line because of the depth of the superstructure.

Is not having the front of the spread footing below the frost line a concern? Does the quality of the fill for the MSE wall reduce the concern for frost heave? Because the back of the footing is well below the frost line, is the entire footing considered "good enough".

Any clarification or thoughts would be appreciated.

Thanks.

 

[PEinc]

If you build the MSE wall with preferred soils (granular), there should not be any frost heave. In any case, check with the state DOT standard details and talk to an MSE wall supplier.

 

[jdonville]

RichBridge,

See the FHWA MSE design guidance - FHWA NHI-00-043 - for example design geometry for this situation. Also, check your state DOT design/construction guidance and wall supplier design guidance for examples of standard practice and acceptance criteria.

As PEInc states, there should not be any frost action using the select granular backfill recommended for use in MSE applications.

Jeff

 

[Boonie]

Use free draining stone for the fill. There are also methods to transfer the tensile force from the reinforcements behind the footings and allow your shallow foundation to be buried deeper.

 

[MichSt]

Rich – Here are some examples from Ohio DOT for you situation. See figures 330, 331, 332 from the ODOT Bridge Design Manual. Here’s the link. Click on the figures on the side of the page to open up pdf files with the actual details.

http://www.dot.state.oh.us/se/BDM/BDM2004/sec300f3.htm

There are examples of spread and pile supported footings there.

 

[Panars]

You'll notice that in Figure 332, a minimum 6" embedment for the footing is required. This is okay because Ohio DOT uses a (relatively) free draining backfill material for the MSE wall.

 

[RichBridge]

Thanks for the info everyone.

Indiana doesn't seem to have any standards with a footing without piling (at least I can't find any) so I'm having to rely on other sources at this time. I'm only at the preliminary stage now so as I get further along I'll work with INDOT to see what they will require.

I was just concerned about the footing depth, but the backfill requirements for the MSE wall seem to take care of that.

 

[casimmons]

How tall is the wall and how much load will the abutment have? Your wall designer will need to consider the effects of the abutment on the wall. Also your statement that the DOT does not have any spread footing details would imply that deep foundations are typically used for these situations. Are you sure that shallow foundations are appropriate?

 

[RichBridge]

Yes, the loading of the footing will need to be supplied to the wall designer. The walls are for a road overpass and a railroad overpass. The total height of the tallest wall is around 36 feet.

It was actually the DOT that brought up the use of spread footings on the MSE walls...there just aren't any standards. I think typically they have used piling and there are some details for that design. If the pressure from the footing is too great for the wall itself to handle, piling will have to be used. Although I think I remember reading the original MSE walls utilized a spread footing and the added pressure actually helped the strength of the wall reinforcing. I'm not an MSE wall designer so that statement might not be true.

This is still in the preliminary stage, so I'm sure I'll get feedback from the DOT.

 

[Panars]

I have heard that Indiana DOT is watching what Ohio DOT is doing with MSE walls, so you might check out the following presentation from Ohio DOT on MSE Walls. Specifically look at Slide 28 on when Ohio DOT will consider putting bridge abutments on spread footings at MSE walls.

http://www.dot.state.oh.us/se/MSEWALLS/MSEWALLS.htm

ODOT Design & Construction Requirements for MSE Walls (OTEC)

If the bridge is supporting normal vehicular traffic, I would expect you should be able to support the abutment on spread footings. However, if it is supporting railroad traffic, then I am not sure you can.

 

[RichBridge]

I saw that presentation when I was searching for information. I have single span, new construction bridges for vehicular traffic so it seems to fit the criteria to be able to use spread footings. I used some of the dimensions in that presentation regarding how far away from the wall to set the footing to get my preliminary bridge length.