Helical Pier Application 1

[RFreund]

I’ve attached some project specific information where we would like to use a unique application of the helical pier. I’ve attached more information than necessary as I am really just after the basics and discussing feasibility.
Project Scope:
Our client would like to install a big block segmental wall adjacent to the property line. The low side of the wall is ‘our property’ the adjacent side is the high side. On the high side of the wall there is an existing structure. We have permission to work on the adjacent property and would like to install temporary shoring to install the segmental wall. We do not want to use driving or vibrating required shoring. We would like to use a helical pier that maybe removed when the wall reaches a certain point. We have discussed using either a cantilevered secant pile wall type system with larger shaft diameters or an anchored soldier pile and lagging approach. We discussed this briefly with a contractor (Elite Piering) and they seemed to prefer the anchored soldier pile idea as they were not sure what large sizes were readily available to do a secant pile wall. I should mention that there is bed rock 10’-20’ feet below the bottom of the excavation. However the excavation height is not very tall 6’ +-.

Questions:
1. Do these approaches seem reasonable?
2. Is there a method of analysis/design you would recommend for evaluating the lateral pressure for this type of system. Because these are not very deep I was thinking that using a Broms type method (similar to the California Trenching and Shoring manual) or the FWHA Geotech. Circ. 4 (reese-wang or Broms eqns) would be reasonable.
3. Any general comments?


EIT

http://www.HowToEngineer.com

 

[RFreund]

2

EIT
www.HowToEngineer.com

 

[RFreund]

3

EIT
www.HowToEngineer.com

 

[RFreund]

Can you upload multiples at once?

EIT
www.HowToEngineer.com

 

[FixedEarth]

RF;

I thought you purchased Azizi's "Engineering Design in Geotechnics" last year? All you need are on pages 367-378. But first, you need to get the earth pressure and surcharge envelope from the project geotechnical engineer. If you are the one who has to develop the earth pressure envelop, see Chapter 6. Once you do a one level tieback design by hand, it is easy to program it and move on to 2,3, 4 levels of tiebacks.

For your short exposed heights, you may consider cantilevered soldier beams.

I found Caltrans and FHWA methods to be unnecessarily complex and conservative.

If you want to check your answers with a software, try the #8, "substructural design" at

http://www.dcalc.us/ProgramDescriptions.html

- they are great programs and I use them on a weekly basis. Highly recommend them!

Also Google SBWALL, Supportit, TBWALL, PYWALL and Shoring suite.

 

[RFreund]

Wow, you have a very good memory as I did purchase the book. I enjoy the book, although I've only used certain parts. For some reason I was thinking that because the helical piers would be semi-flexible that I would need to use a different design approach. As for cantilever soldier beams - I contacted a couple contractors and they expressed a concern of settlement when driving or vibrating in the soldier piles. I figured helical piers may be a cheaper/faster alternative than drilling in soldier piles as it is for such a short length of wall.

EIT

http://www.HowToEngineer.com

 

[dcarr82775]

You are thinking of using the helicals as the anchors, and not the vertical piers correct? I would never push horizontally on a helical pier and expect anything in return. Helicals work fine as low capacity tiebacks.

 

[RFreund]

No i was thinking the helicals would be verticals and tie back anchors. You think this is no good? It does say that they are available in up to 10" diameter. Still too flexible?

EIT

http://www.HowToEngineer.com

 

[dcarr82775]

The helical plate leaves a path of disturbed soil in its wake. Yes the industry has test data showing it is sufficient to brace the shaft against buckling, but I have seen no data about the disturbed soils resistance to lateral loads. I believe how much the soil is disturbed depends on how hard the soil is (harder soil will be more disturbed), but just my opinion.

I think the pier will move laterally in the disturbed zone(low passive resistance). With a building directly above I wouldn't take the chance of movement.

 

[RFreund]

Thanks dcarr I didn't think about that.

I have contacted AB Chance for their thoughts. I will let you know what I find out. So you think it would be best to drill soldier piles or secant wall (as you suggested before in regards to a different post of mine I believe)

EIT

http://www.HowToEngineer.com

 

[RFreund]

Quick side question - Do you have a base example for cantilevered or anchored soldier piles? Usually I use the 1990 Cali Trenching and Shoring. I know that it is just active on one side passive on the other however it seems like there are number of examples that are slightly different.

EIT

http://www.HowToEngineer.com