Help with sheet pile wall along channel 2

[MikeE59]

I am hearing totally different opinions for how deep sheet piling should be for a retaining wall along a channel. Wondering if anyone could help. First 15 feet of soil is loose to firm sand with gravel, then a 5 foot layer of peat, then 10 feet soft to medium clay. The pile wall will run along the inside edge of an existing boardwalk. The boardwalk is 6' wide and sits on two rows of wood piles on 6' centers. Do not know how deep these piles go. The water level is usually 6' below the boardwalk but this varies from 3' to 9' depending on lake levels and weather. About 5-6 feet below the boardwalk rip rap begins and runs out to a channel at about a 30 degree angle. Channel is 6-8 foot deep given current water levels. Tried to include picture below. Any help much appreciated.

http://i57.photobucket.com/albums/g213/mlelliott1/SheetPileWall_zpse31d8d11.jpg?t=1393168495

 

[bridgebuster]

In a loose material your embedment could be as much as twice the retained height. In a very dense material the embedment could be around .75 of the retained height. The USACOE has manuals online that explain sheeting design.

 

[MikeE59]

So would the retained height in this case be the distance from the top of the boardwalk to the rip rap, or from the top of the boardwalk to the average water level, or from the top of the boardwalk to the low water level. Would you need a whaler and tiebacks?

 

[bridgebuster]

The retained height is from the top of the boardwalk to the dredge line of the river. Why the tie rods through the timber piles? You could use tie rods through the sheeting it will reduce your embedment depth but you have to look at the added costs for tie rods and deadmen vs additional depth of sheeting.

6x6 solid fender seems like overkill. You shouldn't have a tie rod coming out it, as it poses a hazard. Also you'll need another line of bracing for the fender.

 

[MikeE59]

Everything black in the drawing is existing. The tie rods through the timber piles are existing. We are looking to replace a retaining system that is prone to failures. You'll find our current design interesting. A 7' chain link is strapped to the boardwalk beam closest the shore. It extends down about 4' and then tucks under the soil. Landscaping fabric is on the inside of the fence. The fencing herniates and tears off the beam creating sink holes.

I want to make sure the new design will last a long time. The contractor is proposing a 10' deep sheet pile wall. They would cut through the existing tie rods to put the sheet piling in and then reweld the tie rods. The top of the sheet pile wall would attach to the boardwalk beam. I would say that the bottom of our channel averages 10'-12' below the boardwalk. It seems to me that you are saying it should be considerably deeper.

 

[cvg]

you may want to assess scenarios that you havent considered already. for instance, erosion of the slope or rapid drawdown. suggest looking at the USACE publications below

EM 1110-2-2502 RETAINING AND FLOOD WALLS

http://www.publications.usace.army.mil/Portals/76/Publications/EngineerManuals/EM_1110-2-2502.pdf

EM 1110-2-2504 Design of Sheet Pile Walls

http://140.194.76.129/publications/eng-manuals/EM_1110-2-2504/toc.htm

 

[PEinc]

You really need to hire an engineer with bulkhead design experience. There are other things to consider besides what is shown in your sketch. Is the sheet piling to be cantilevered or tied back? If tied back, where will the wale be located? Will it be in front of or behind the sheet piling? Is there room for the wale in front of the sheet piling? What and where is the existing tie rod and deadman system? Is the existing tie rod and deadman system sufficient for the new structure? What is currently retaining the soil between the tiedback timber piles? The answers you have received above could be affected by your answers to my questions.

http://www.PeirceEngineering.com

 

[MikeE59]

I'll do my best to answer these questions. I was hoping someone with experience in this field could tell me 10' piles seem reasonable or they are too short given your application. I'm on a condo board with non-technical members who tend to believe the contractor. My gut feeling with what I've read is that 10' is to short and would tend to push out at the bottom, but I'm no expert. The technical design documents referenced are quite intimidating someone not well versed on the subject matter.

Here is what the contractor quoted that they would do:
Mobilization of equipment & materials
Excavate behind existing timber deck to tie-back grade
Drive new SKL 12 x .217 thk x 10’ long sheets
Cut through tie-back rods to drive sheeting and re-weld rods back together
Weld a new C6 x 10.5# cap atop the sheeting
Backfill with existing excavated material

Given that I will try to answer the questions you posted and hopefully someone can give me more thoughts.
Is the sheet piling to be cantilevered or tied back? Cantilevered.
If tied back, where will the wale be located? None, just a C6 x 10.5# cap
Will it be in front of or behind the sheet piling? N/A
Is there room for the wale in front of the sheet piling? N/A
What and where is the existing tie rod and deadman system? There a are two wooden piles driven every 6' under the existing boardwalk to support it. Do not know how deep they are driven. Each wooden pile on the shore side has a tie back through it about 3-4' down that runs to a deadman about 15-20' back in the ground.
Is the existing tie rod and deadman system sufficient for the new structure? No idea, but it is 20 years
What is currently retaining the soil between the tiedback timber piles? The current retaining system is prone to failures hence we are looking to upgrade it. You'll find the current design interesting. A 7' chain link is strapped to the horizontal boardwalk beam closest the shore. It extends down about 4' and then tucks under the soil. Landscaping fabric is on the inside of the fencing. The fencing herniates and tears off the beam creating sink holes. This design is interesting in that it tends to pull down on the boardwalk rather than press against it. It also allows water to pass through so you build up very less hydraulic pressure and if pressures get too great it ruptures rather than damage the boardwalk. I'd hate to upgrade to a system that pushes the boardwalk over when it fails.

 

[cvg]

you need an engineer to design the retaining wall and you need (the contractor) to pull a permit. the building department will probably require drawings stamped by a registered engineer. pulling the permit is for your own protection and yes it will cost more, but worth it.

 

[PEinc]

Good answer, cvg. The wall must be designed by an P.E. If I were the contractor, for my own protection, I would insist that an engineer design the wall.

http://www.PeirceEngineering.com

 

[MikeE59]

Does anyone know any companies in northern ohio that would do this type of design. Any idea what a design should cost.

 

[bridgebuster]

Here's a listing of engineering companies in northern Ohio.

http://www.thomasnet.com/northern-ohio/engineering-services-civil-26181024-1.html

I think 40 hours )~$5,000) should cover the work, assuming no additional subsurface investigation is needed.