Self Supporting Arch Shoring?? 1

[Sentinel_7]

Good day Everybody.

I am looking at designing a similar shoring solution to the one in the photo, except I will be using sheetpiles.

My area is has restricted access and space with neighbouring structures so neither anchors nor props is an option. Hence I looking to use the strength of the arch shape.

I was wondering if someone can refer me to some theory or published articles that I can apply to design the shoring system cost effective.

Just assuming it is a cantilevered wall amd using the apex of the arch will result in over conservative structural elements and unrealistic predicted wall deflections.

Looking forward to your responses!

 

[hokie66]

Sheet piling has most of its strength in the vertical dimension. Horizontally in compression, not so much. And with your approach, how would you resolve the thrust at the ends?

 

[PEinc]

An arch needs abutments. Your SSP would have no abutments. You may be forced to use a heavy, drilled-in, soldier beam or tangent pile wall.

http://www.PeirceEngineering.com

 

[Sentinel_7]

Thanks PEinc & hokie66

I sort of came to the same conclusion but was hoping there might someone more clever or some literature out there that has encountered this problem before.

In terms of the abutments I am toying with the idea of installing a few metres of sheetpiling extra on both ends that will not retain any soil and instead work as a friction element to act as the abutment.

 

[PEinc]

I don't know how well your "arch" will work with SSP that can be squeezed narrower because of the possible deflection or rotation at each "pinned" interlock. An arch would be in compression which would squeeze the individual SP sections like an accordion.

http://www.PeirceEngineering.com

 

[Sentinel_7]

Yes, that is a risk, but I will have two rows of C200x75 Channel walers rolled to the arch radius and welded to the wall to help with that.

 

[PEinc]

Good luck calculating the frictional or passive resistance of a couple SSP sections being loaded in the plane of the SSP wall, below finished grade in front of the wall. Take good notes and monitor the wall so you can write your book or apply for a patent.

http://www.PeirceEngineering.com

 

[Sentinel_7]

Thank you for the advice and you thoughts.

I will certainly monitor it very closely as we excavate down... but based on original image I posted someone has done it successfully before.

 

[PEinc]

Not necessarily an arched wall. Those may be just big, long WF soldier beams drilled in place to make a cantilevered wall about 20' to 22' high (a tall, but not too uncommon, cantilevered wall).

http://www.PeirceEngineering.com

 

[r13]

Maybe this culvert supplier can help!?

 

[jayrod12]

The original picture did not account for arching in that sense from what I can see. As PEinc indicates, likely just large steel soldier piles in deep concrete plugs. Quite common actually. It does not take into account any arching strength, but may consider some soil arching on both the retained side above the cut, and the resisting side below the dredge line.

I would listen carefully to anything PEinc says about retaining walls and temporary shoring. He is the "local" expert on that stuff around here.

 

[Sentinel_7]

Thank you all.

I have still designed my wall as a cantilever due to the lack of information/theory on arch type structures.

I was hoping to adjust/optimize what I have done because the arch must contribute in some way to the strength of the wall as a whole. Looking at it as a pure cantilever system can be considered overconservative by some as they will ague the arch will have an effect.

I will monitor the performance of the wall and compare actual deflections at specific depths compared to my design as a free cantilever. Hopefully it will give me some insight and I will be able to design a more cost-effective solution for the client next time around.

 

[SlideRuleEra]

Looking at it as a pure cantilever system can be considered overconservative by some...

Maybe overconservative but probably more cost-effective than incorporating arch effect. Spending money on "oversized" permanent materials instead of spending even more money on time-consuming, complex construction (excess labor & equipment cost) is almost always a bargain.

http://www.SlideRuleEra.net

 

[PEinc]

Consider also if your "arched wall" design needs to be reviewed and approved by an engineer (DOT, local building official, other government agency?) who probably knows much less than you do about non-gravity retaining walls. What references will you be able to cite to show your design method is valid? Remember: K.I.S.S.

Also, what happens to the entire wall if someone digs in front of one of the "abutments" to do some utility work?

How will you design the main run of individual sheet piles if the sheets are totally in compression?

I agree with SlideRuleEra. I smell trouble.

http://www.PeirceEngineering.com

 

[STrctPono]

I have still designed my wall as a cantilever due to the lack of information/theory on arch type structures.

I think this is prudent. In order for an arch to function, it needs to be able to resist the "thrusting" action at the ends of the arch. This is either accomplished by transferring this thrusting force into the foundation or by resisting this thrust by tying one end of the arch to the other side (similar to a tied-arch bridge). Your system would have neither of these two abilities.

Furthermore, the photo that you show appears to be a cantilever soldier pile wall with HP piles and timber lagging between. No structural arching action here. Just happens to be on a curved plan.