Sheet Pile Support by Vertical H-Beams 1

[Khurram Shehzad]

We have a 8m deep excavation in sandy soil, as per design we need to provide two levels of bracing. At top level (at 2m depth) we are using Deadman anchors. However, for 2nd level (waler is at 5m depth) our client is asking to install the H-beam in front of sheet piles so that load can be taken by the vertical H-beams. This is to safe the space inside excavation. We are not allowed to install the ground anchors. So now I have to do the Vertical beams calculation but I am unable to find any calculation related to this, can any body please help. I am attaching one schematic drawing for under standing. I need the calculation for H-Beam (blue color) in drawing.

 

[SlideRuleEra]

...I have to do the Vertical beams calculation but I am unable to find any calculation related to this...I need the calculation for H-Beam...We are not allowed to install the ground anchors.

Drawing is not attached.

If you omit both levels of support (at 2m and 5m depths), the sheeting is cantilevered out of the soil.

The H-Beam (HP) will either have to be welded to the sheeting and driven with it or driven separately from the sheeting. Both approaches have significant problems.

IMHO, forget the HP and see if heavier (higher moment of inertia) sheeting (say, PZ or AZ series) is available that is suitable for cantilever loading of 8+ meters without the HP. Also check to see if soil properties allow the higher (cantilever) loading. For cantilever loading, assume sheeting embedment will be at least 8 meters and the line of support for the sheeting will make the cantilevered length of sheeting greater than 8 meters (as determined by soil properties).

http://www.SlideRuleEra.net

 

[geotechguy1]

Just to clarify, are you using an h-beam horizontally across the excavation as a prop or vertically in front of the sheet piles

 

[Khurram Shehzad]

SlideRuleEra/geotechguy1, thanks for the reply drawings is attach. This design is as per our available sheet pile material. We can not spend more money to change our sheet piles, so most of the factors are unchangeable now except the H-beams. So kindly let me know if there is any thing you can share about the calculations.

Update. I used the approach in Das Foundation engineering book for the cantilever sheet piles without any backfill and apply on this h-beam but the moment is coming so high that I have to apply very big section at 1m spacing.

 

[jayrod12]

Large sections for 8m shoring is what I would expect. That's a no joke wall. Around here in my local soil conditions, cantilevered soldier piles are only good for around 4-4.5m before it starts to get extremely ridiculous for the concrete plug diameter versus spacing.

How long is the excavation?

 

[SlideRuleEra]

Khurram Shehzad I see the top wale (2m depth) can be used, sorry for assuming it could not.

The drawing shows excavation depth as 10m, but the original post states 8m. In either case, I don't believe the vertical HP used on undersized sheeting will be practical or safe. However, that is just my opinion. Maybe others have a way to make good use of a vertical HP.

What I would do (if heavier sheeting is not an option) is to forget about using the HP vertically. Instead see if using the HP horizontally as a third or even fourth elevation of wales (adjust elevation of all wale, including the 2m depth as required). This would lower stress in all wales, maybe allowing smaller members (perhaps increasing space in the excavation.) May or may not work, won't know unless you do the math.

One thing I would do for certain... the decision on what to do would be based on accurate assumptions and correct calculations. What a client "wanted" or I "thought" are worthless. People get killed if this type work is not done right... the first time.

http://www.SlideRuleEra.net

 

[PEinc]

Very inefficient design. The upper tier of tie rods will support very little load while the lower waler will support most of the load. The amount of passive resistance from the vertical H=Pile is insignificant compared to the passive resistance provided by the SSP. If possible, try to use a heavier, possibly deeper, SSP with the single tier of tie rods and deadmen. Also, the deadman should be back far enough that the wall's active zone and the deadman's passive zone do not overlap. Otherwise, you will have reduced passive resistance from the deadman.
If you really need a lower tier of bracing, consider inclined raker braces that bear on heel blocks.

http://www.PeirceEngineering.com

 

[Khurram Shehzad]

Thanks all of you for your input. We do not have free space inside the excavation for horizontal or raker bracing that is why this vertical beam is under consideration. I am also attaching the image of the concept I am refereeing. Actually we have use this method in one previous excavation but just based on experience by our team.

 

[PEinc]

Khurram Shehzad, good luck with that design! The sheet piling and the soldier beams would be pushing on the same soil for passive resistance. I am not sure how you will model that unless you assume that the sheet piling has no embedment (this simplifies the analysis) and the soldier beams have about 3 tiers of horizontal walers against the sheet piling. Without even considering any surcharge loads and using average granular soils and no ground water, I get very large soldier beams at 1m spacing. With 3 levels of bracing, the sheet pile size needs not be very large. I assumed a trapezoidal earth pressure on the sheet piling. You could reduce the soldier beam size if you assume a triangular loading on the sheet piling but with 3 levels of bracing and some pre-loading of the soldier beams and walers, I don't think triangular earth load is appropriate.

http://www.PeirceEngineering.com

 

[Khurram Shehzad]

PEinc thanks, yes i also got very large beams with 1m spacing. We are pushing our client for any other bracing option then this. Thanks all of you for your time and help.

 

[JedClampett]

My advice is to listen to PEinc.

 

[PEinc]

Thank you, JedClampett.

Khurram Shehzad, read SlideRuleEra's first response. However, PZ and AZ sheet piling will not be strong enough. You could try designing a heavy-duty sheet pile combi-wall made of interlocking sheet piles with either interlocked WF beams or pipe piles. Essentilly, the "H-Pile" soldier beam that you are proposing would be interlocked into the single sheet pile wall.
Google "combi-wall" or go to

https://www.google.com/search?rlz=1...hWUSfEDHZJzDDMQjJkEegQIDBAC&biw=2560&bih=1249

For a cantilevered combi-wall without any bracing, you could design for triangular earth pressure. You also have an unlimited selection of WF king pile sizes to interlock with the SSP.

Also, please confirm if the wall has an 8 or 10m exposed height - big difference!

http://www.PeirceEngineering.com

 

[Settingsun]

Can your top anchorage take enough load to have a single bracing level? If so, you could run the vertical beams up to the top anchor rather than cantilevering them. That would effectively be a single anchorage combiwall.

 

[Khurram Shehzad]

PEinc, sorry by mistake it shows 10m, excavation is 8m deep. I am proposing them for a higher section but it will cost money, this proposal is under consideration.

steveh49, noted we can extend the beams to attach with the deadman, I will check the calculations.

 

[EireChch]

Khurram - its not a case of "it will cost more money" as if it is a extra unnecessary additional cost that the client will moan about. Its a case of this is the minimum that is required to construct a safe excavation (with internal space as the client requested).

 

[Khurram Shehzad]

EireChch, you are right, it is not the case of money only. We are also analyzing the available options. But cost is also a factor we can not ignore, we have to find a solution which will be safe and less costly. So if there is no other way than getting heavier section defiantly we will buy that. We have also asked our client to do step excavation so that excavation depth can be reduced. We have to be safe otherwise there are huge safety and financial consequences.

I am checking with you guys because I always find it very helpful and informative, this form always have some different ideas. Thanks for everyone help, I will post the final solution once decided by my company and client.

 

[SlideRuleEra]

We are also analyzing the available options.
So if there is no other way than getting heavier section defiantly we will buy that.

As a Bridge Contractor, spending our own money (not a Client's), I quickly learned, first from my father then for myself:

Problems which can be solved with money are usually best solved that way.

In this case, spend the money. Otherwise you will slowly "throw away" far more (of your Client's) money in design & construction time / labor / equipment cost looking for the "perfect" answer, which may not exist.

http://www.SlideRuleEra.net

 

[JedClampett]

Old saying, "There's never enough time to do it right, but there's always time to do it over."
In your case, I'd replace time with money.

 

[EngMan40]

You can install another row of sheet piles behind the front row and connect the two with sheet piles to form square cells (like a cellular cofferdam). link for the design manual from USACE:

https://erdc-library.erdc.dren.mil/jspui/handle/11681/10842