Temp Retaining Wall - CSX Cooper E80 Railroad Load

[ARS97]

We're quoting a project that will require a temporary retaining wall to allow for construction access. This temporary wall will be nearby a railroad, and the geotech has recommended that the CSX Cooper E80 Railroad load be applied to this wall (in addition to the typical active soil pressure) to account for the lateral surcharge from the tracks. The geotech also has recommended that the wall generally consist of drilled shafts that extend into a rock socket, H-piling embedded in the drilled shaft that are cantilevered to the surface (about 15'-20'), and wood lagging in between the H-piling. (See page 1 of attached PDF.)

The CSX Cooper E80 railroad load is a typical strip load consisting of a uniform pressure of 1,882 psf over a 8.5' width. Boussinesq's Method is to be used to estimate the lateral pressure on the wall. (I used AASHTO's method - see page 2 of attached PDF.)

I made an Excel spreadsheet that computed the lateral pressure from this strip load (AASHTO method) for depths up to 15' and for multiple offset distances. I then plotted the lateral pressures on a chart. (See pages 3 & 4 of attached PDF.) I noticed in the AASHTO commentary that this procedure is suited for a restrained top (at-rest pressure), which for this type of wall (flexible) yields very conservative results. I am assuming that I can reduce these lateral pressures by a factor equal to the ratio between the at-rest coefficient (3.25) and the active coefficient (0.31), which is about 3.25 / 0.31 = 10.5. Is this sound reasoning?

NOTE - the attached PDF does NOT show the adjusted pressures.....it still shows the at-rest pressures calculated with the AASHTO procedure.

 

[GeoPaveTraffic]

First, many Class 1 US railroads have their own method of calculating loads on any walls within a certain distance of their tracks. They use elastic theory to determine the lateral wall load due to the track. Additionally they have very strict deflectionlimits that usually preclude the use of cantilevered walls.

As for your proposed reduction, there is no reduction in surcharge load due to wall flexibility.

Mike Lambert

 

[ARS97]

Here's an portion of the CSX spec referenced by the geotech. Look at the 2nd page, part d - this looks identical to the AASHTO procedure, which, as GeoPaveTrafiic mentioned, doesn't involve any reduction.

 

[ARS97]

NOTE - I found an error, which changed things dramatically. In the AASHTO procedure, I was taking the angle "gamma" as the total included angle from the wall to the far side of the strip load. This is supposed to be only taken to where the angle "alpha" ends. This drastically reduces the applied pressure to the wall.

 

[ARS97]

Attached is the updated pressures.....makes MUCH more sense.

 

[RFreund]

FWIW ->
I would be surprised if they let you use a cantilever system, if they do, usually the deflection limits are very difficult.

EIT

http://www.HowToEngineer.com

 

[ARS97]

Well, the tracks are on private property (power station).....CSX just uses the tracks.

 

[hokie66]

I agree that cantilevered walls are not used in these situations. I would look at installing temporary anchors.

 

[Once20036]

I doubt that your at rest coefficient is 3.25, that looks much more like a passive coefficient.
Restraining the top of the wall or not would be the difference between the active pressure and at rest pressure. I`d expect this ratio to be much closer to 1.5 than 10.

 

[TehMightyEngineer]

Agreed, I would expect the at-rest coefficient to be something like 0.5.

Maine EIT, Civil/Structural.

 

[ARS97]

Once20036 & TehMightyEngineer - yep.....mistake on my part. I scribbled things down a little too quickly. My geotechnical skills are a little rusty.

I'm starting to wonder if the geotech consultant made a poor recommendation in regards to the wall type.......

 

[RFreund]

I suppose it also depends on how far from the tracks you are....

EIT

http://www.HowToEngineer.com

 

[ARS97]

RFreund - right now it's looking like about 15'-20' will be the closest.

I'm going to try and contact someone within CSX (engineering personnel) that can hopefully lead me in the right direction. I have a feeling that this wall type and general recommendation from the geotech wasn't vetted by CSX. Although the customer (power station) owns the property & tracks, I'm sure CSX would want to have input since they're using the tracks.

 

[MJ23struct]

Use caution with the "2p" in the equation which is for rigid / non yielding walls.

For flexible walls (sheet and soldier pile) "1p" may be appropriate.

For semi-rigid, 1.5p.

 

[ARS97]

MJ23struct - can you provide some insight into what you mentioned about "2p"? Is this discussed in a commentary somewhere?