Sheet Pile Retaining Walls - LRFD 1

[jlaw]

PennDOT has changed their Support of Excavation Specification to require that sheet pile retaining walls be designed using LRFD. Having no experience with LRFD in this application, I'm looking for references that would explain / teach the LRFD application to sheet pile design.

Pile Buck is not an option. They billed my account, did not send the manual but did give me access to a website. They advertised that the new manual would contain LRFD but it is only a paragraph at the end of a chapter regarding sheet pile.

 

[PEinc]

Get PADOT's Design Manual 4 and FHWA's Engineering Circular No. 4. Both should be available on-line. LRFD is so new that there isn't much else around that explains how to design sheeting that way. More important than LRFD, FHWA and especially PADOT are using the new, unsymmetrical, trapezoidal shaped earth pressure diagrams for braced and tiedback walls, for both single tier and multi-tier walls. With the new diagrams, the shape of the trapezoids change with different brace and tieback locations. This makes it difficult to use a computer program because you have to hand recalculate and then re-enter the pressure diagram into the program every time you try a different brace or tieback location. This makes it hard to optimize the brace or tieback locations and design loads. In addition, tieback anchors are installed to an unfactored design load and then tested to as much as 133% of the design load. If you design with factored tieback loads, you won't know what the test load should be. Therefore, we design the wall twice for PADOT jobs. Once with LRFD to get the beam sizes and lengths and once more with alowable stress to get the unfactored tieback loads. With the unfactored tieback design load, I can then determine the tieback test load. This is extra work, but PADOT doesn't care. It's only taxpayers' money.

 

[UcfSE]

Does the DOT offer any downloadable programs for LRFD design? I'm not too familiar with DOT projects but as an example, FDOT requires LRFD for retaining wall design and offers a free MathCAD worksheet to design the retaining wall with LRFD.

 

[jdonville]

jlaw,

Contact FHWA by telephone to order a free copy of HI-98-032. Not available for download, unfortunately, but a good reference for explaining the philosophy and calculation difference between LRFD and working or allowable stress design. See

http://www.fhwa.dot.gov/engineering/geotech/pubs/hydorder.cfm

for the Report Center contact information

See also the fhwa LRFD site at

http://www.fhwa.dot.gov/bridge/lrfd/index.htm

and the AASHTO LRFD site at

http://bridges.transportation.org/?siteid=34&pageid=229

Hope this helps,

Jeff


Jeffrey T. Donville, PE
TTL Associates, Inc.

http://www.ttlassoc.com

The views or opinions expressed by me are my own and do not necessarily reflect the views or opinions of my employer.

 

[Panars]

There is a reference manual for an NHI course that describes the design of nongravity cantilevered walls. However, it is not available online (I think because they are still revising it). It is the reference manual for NHI Course No. 130082 and it's title is "LRFD for Highway Bridge Substructures and Earth Retaining Structures". Section 6.3 covers sheet pile walls. Perhaps you can find someone at PennDoT that has attended the course and can give or loan you a copy.

Have you looked at the AASHTO LRFD specification yet?
If you don't have a copy yet, you will need one soon as FHWA is (effectively) mandating all DOTs to use LRFD starting in 2007.

Nongravity retaining walls (sheet pile walls) are covered in Section 11 of AASHTO LRFD. However, the loading is in Section 3.

 

[VoyageofDiscovery]

Does anyone truely understand this LRFD approach for earth structures?

Is this trend just a policy we are all following like sheep? Does anyone want to comment on its validity for these type of earth retaining structures utilizing passive pressure as resistance.

VOD