Sheet Piling

[Heldbaum]

Hello folks,

In a nutshell, owner of the townhouse in new york city wants to enlarge his house vertically and horizontally, meaning going down around 12' in the existing basement plus he wants to extend the basement all the way to the rear (where there is no basement now) what means he would have to excavate roughly 25'-30' down over there which is a lot of course. There are adjacent buildings, he wants to avoid underpinning, ground water table is below expected bottom of excavation. The soil is class 3a sand with silt and gravel. No way to bring any heavy equipment in.
I am thinking about sheet piles that are pushed by a hydraulic jack. We would install two steel beams going from wall to wall (or new steel column to new steel column)and one beam across and attach hydraulic jack to its flange. We would put enough ballast on the top of those beams plus we could use the self weight of the exist. building. Then we would do that in stages pushing 8'-10' long sheet piles next to each other and brace them from wall to wall..then we would excavate 5'-6' so the first pile's tip is still below the dredge line and push another pile next to it..Please see attached sketch of what I would like to do. I think that way we would reduce a friction and make those sheet piles driving easier.. then the question is how to connect those piles together (moment connection) so it can withstand soil pressure and provide watertightness etc.
We would also pre-drill the soil before jacking up operation. I think we would need at least 30-40 tons force to push it it..

It is just my imagination working so please share if you have any thoughts on that issue. It will be greatly appreciated. Thanks!

Jack

 

[SlideRuleEra]

Heldbaum - IMHO, the proposed approach is not a good idea.
High risk (many complex steps, with a lot of unknowns).
Serious consequences (make an error...collapse the structure, injuries / fatalities possible).

http://www.SlideRuleEra.net

http://www.VacuumTubeEra.net

 

[dik]

How far to property lines? With limited access, it may not be possible to install a sheet piling wall or to even undertake the project. Don't minimise the cautions that SRE has outlined.

Dik

 

[Heldbaum]

SlideRuleEra - yes I know it's a high risk..So you think it is not even worth considering?

Dik - it's a typical 25x100 lot with adjacent properties..there is a party wall on one side..

 

[SlideRuleEra]

Heldbaum - No, I would not consider this proposal. We can talk about the details if you want to, but I'll just mention one for now:

High surcharge load on the soil. And, it can vary while the work is in progress. As I understand the plan, jacking will (in part), "...use the self weight of the existing building." While jacking is underway, the surcharge is reduced, when the jacks are unloaded, surcharge returns. Along with this goes the unknown of what will happen to this building during jacking - probably not designed for uplift. Also, possible surcharge from adjacent structures.

http://www.SlideRuleEra.net

http://www.VacuumTubeEra.net

 

[Heldbaum]

SlideRuleEra - thank you for your answers, give me more I would like to use maybe 30-40% of the existing bldg's weight, not to cause uplift..rest it would be a ballast added to the steel frame.

 

[SlideRuleEra]

Uplift force can cause damage without actually lifting the building, say separate mortar joints in masonry.

How to calculate the building's weight? Are there plans? Have modifications been made over the years? Are the materials used in the building's construction in "as-new" condition?

(Estimated) to need "at least 30-40 tons force". So, 40+ tons may be needed. How much of the total is ballast? How will ballast be brought in? Maybe, 20 lb. sandbags, by hand - since there is "No way to bring any heavy equipment in." Is there enough room in the workspace for the ballast?

"...ground water table is below expected bottom of excavation." but the sheeting needs to "provide watertightness". I'm not concerned with leakage, it's about unplanned for hydrostatic pressure on the sheeting - either during construction or later.

"...the question is how to connect those piles together (moment connection)..." What is the answer? For sure would not begin the project without a proven answer. Steel sheet piling has been used on large scale since the 19th century. Is there a proven answer, I don't know of one. Doubt the client is interested in having the property being used for a "high risk" research project.

I'm not trying to convince you of anything, just offer some points to think about. I worked as a Development Engineer (as in "Research and Development") for 4 years full time, then 18 more years part time. The right way to approach a problem using a novel approach is to "do your homework" first. In this case, see if you can find anything like this proposal that has been used successfully. Determine or calculate what you can - ground water level, pertinent existing building details, surcharge loads, soil/water pressure at the appropriate depths, etc.

Then use your imagination to make informed concepts of what may work. Follow this up with calculations to see if your imagination is playing tricks on you - it can.

http://www.SlideRuleEra.net

http://www.VacuumTubeEra.net

 

[PEinc]

Recently designed a similar project to make a 30' deep basement with buildings on 2 sides, an historic façade on the front, and a narrow street to the rear with residences across the street. The job needed tiedback underpinning on the sides, tiedback sheeting and underpinning on the front façade side, and tiedback sheeting at the rear side. I don't see SSP being an option for your project. The press-in SSP equipment has limited availability. You probably can't install the SSP close enough to the adjacent buildings to not reduce the basement area significantly.

http://www.PeirceEngineering.com

 

[DETstru]

Can you get equipment back there to install a secant pile wall?

 

[Guest262653]

Have you considered a soldier pile wall with cast in place concrete panels and shoring (or soil anchors)? Since groundwater is not a problem, it really looks as the most feasible solution. We have done a lot of designs around my area with this system for very deep and large excavations.

 

[Heldbaum]

SRE - thank you very much.

DETstru - I can't, that's the main problem..

 

[Guest262653]

I still suggest Something like this but with struts only, since the lot is not that wide:
Link

 

[Heldbaum]

avscorreia - thanks for your suggestion. How would you incorporate those soldier piles into the ground?

 

[Guest262653]

When we have really constrained spaces, with the new boundary wall close to adjoining structures, usually it's not possible to install regular wide flange soldier piles in the wall. In these situations, we specifiy micropiles on the outside of the wall to support the wall panels. I'm not an expert in equipment but, for micropiles, you can usually get a small micropile rig through really tight spaces. Here in Portugal they have been used used extensively in renovation works for old buildings in the old city centres of Porto and Lisbon. Maybe you could check with your local contractor to assess feasible options.

 

[Heldbaum]

avscorreia - yes it makes sense. The only thing is how to move and place in the right position concrete panels like that without any crane..?

 

[PEinc]

Heldbaum, here is a picture of the similar job that I referred to in my above response. It shows tiedback sheeting, underpinning, and façade support for deepening an 8 feet deep basement to 30 feet. Installing underpinning and tiebacks does not require large equipment. The soldier beams at the front and rear side of he site were drilled in; but, depending on your required depth, soldier beams can be drilled in with smaller equipment.

Sheet piling and secant pile walls will reduce the footprint of the proposed basement. Underpinning probably will not. Precast lagging panels are usually difficult to install, especially if you have tieback anchors and/or a deep excavation.

www.PeirceEngineering.com

 

[cvg]

why not just soil nails and shotcrete facing. perfect for top down construction. the main issue with this is nails might extend beyond the property line

http://www.deepexcavation.com/en/soil-nail-wall

 

[Heldbaum]

That's the thing that we would like to stay around our property line only. The owner does not want to deal with neighbors. So I guess we cannot use any soil nails/tiebacks in that case..?

 

[PEinc]

Heldbaum, the owner is going to be dealing with the adjacent property owners anyway. Depending on the underground floor levels, the tieback anchors probably would be temporary, but abandoned in place.

CVG, soil nailing should not be used to support buildings that are immediately adjacent to the excavation. The building can collapse as soon as you make the first cut to install the nails. Google Lancaster, PA building collapse.
For a report on this soil nailing job, go to:

https://www.youtube.com/watch?v=spGrSRRbAhg

http://lancasteronline.com/news/for...cle_a83f51e2-2f94-54e8-b26c-3b3dd666fbc3.html

http://www.PeirceEngineering.com

 

[Guest262653]

@Heldbaum
The panels aren't precast. It's all cast in-place against the ground. Here's another picture of the construction sequence:
Link

Here's another picture of a similar situation with tiebacks:
Link