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Sheet Piling

Sheet Piling

Sheet Piling

(OP)
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

RE: Sheet Piling

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).

www.SlideRuleEra.net idea
www.VacuumTubeEra.net r2d2

RE: Sheet Piling

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

RE: Sheet Piling

(OP)
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..

RE: Sheet Piling

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.

www.SlideRuleEra.net idea
www.VacuumTubeEra.net r2d2

RE: Sheet Piling

(OP)
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.

RE: Sheet Piling

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.

www.SlideRuleEra.net idea
www.VacuumTubeEra.net r2d2

RE: Sheet Piling

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.

www.PeirceEngineering.com

RE: Sheet Piling

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

RE: Sheet Piling

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.

RE: Sheet Piling

(OP)
SRE - thank you very much.

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

RE: Sheet Piling

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


RE: Sheet Piling

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

RE: Sheet Piling

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.

RE: Sheet Piling

(OP)
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..?

RE: Sheet Piling

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

RE: Sheet Piling

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

RE: Sheet Piling

(OP)
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..?

RE: Sheet Piling

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/former-empire-tv-b...

www.PeirceEngineering.com

RE: Sheet Piling

@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

RE: Sheet Piling

(OP)
Thank you very much for your input guys.

RE: Sheet Piling

avscorreia, very impressive. It looks like you need very good ground conditions to stay out of trouble.

www.PeirceEngineering.com

RE: Sheet Piling

(OP)
avscorreia - how often do you usually drill the micropiles ?

RE: Sheet Piling

PEinc
Some cohesion is indeed needed for temporary face stability. This is not applicable in loose sands or high water tables. The soils around here (CDG) mostly allow a 12h stability time frame to place the premanufactured rebar panels and in the situ concrete and formwork.

Heldbaum
It really depends on the panel dimension, which in turn will depend on soil conditions. The micropiles are designed for vertical load only, which arises from the panel weight and the vertical component of the soil anchor prestress (minus some friction of the wall panel with the soil). For example, if the primary and secondary panels are 3m wide, we can place the micropiles at 2.0m cc for primary panels. There won't be any micropiles for the secondary panels as these are supported laterally in the primary ones.

RE: Sheet Piling

(OP)
avscorreia - thank you very much. Do you have any reference (book, article) about this method (means and methods etc.) ? Primary and secondary panels - is it similar to secant piles that one pile is reinforced and another one is not? How the reinforcement is placed there? If you know any reference, I'd appreciate it.

RE: Sheet Piling

The main references I have are in Portuguese. We call it concrete Berlin, Lisbon or even Munich-type walls. Here's some information from the Technical University of Lisbon:
Link 1 (look in page 21 and forward)
Link 2

Both primary and secondary panels are fully reinforced. The concept is different from secant piles as it refers only to the construction sequence. Look in page 22 of the reference I provided.

Some design aspects:
- define a proper construction sequence;
- horizontal actions are the same as for a multi-propped or multi-anchored retaining wall, considering Terazghi and Peck envelope diagrams;
- code-compliant reiforcement lap lengths are required between panels and between cap beam and panels;
- the panels must be analyzed for both directions and in every operation during the construction sequence;
- punching shear reinforcement is normally required around the anchor (strut) connection;
- soldier beams (or micropiles) are designed for compression and buckling only in the upper stages;
- soil embedment length of soldier piles (or micropiles) defined considering sufficient geotechnical capacity for vertical loads;
- over thickness of concrete panel must be considered when calculating vertical loads;
- if long-term support is provided by slabs, a proper connection must be designed (post-installed rebar, rebar in wall and unbending for connection to slab, etc).

RE: Sheet Piling

(OP)
avscorreia - thanks for that. Any chance I can contact you via email and discuss the situation/site conditions a little bit more thoroughly..?

RE: Sheet Piling

Before you get too far along in this process, don't forget to check into availability of easements for permanent or temporary tieback anchors.

www.PeirceEngineering.com

RE: Sheet Piling

We could all benefit if the discussion was public. Can't you post your data here?

RE: Sheet Piling

(OP)
Ok sure, I can post it here. I will do that after work.

RE: Sheet Piling

(OP)
Hi guys,

so I am adding two pictures with floor plans and one boring log. It's a masonry building with pocketed wood joists. On the left side we have a party wall that is shared with 3-story building and on the right side there is a 5-story building with independent masonry wall. All buildings, most likely,have cellars at the same level. So the owner would like to deepen the existing cellar of about 10-12'. The basement floor, which is roughly 10 feet above the cellar level, and around 4' below sidewalk, is to be aligned with cellar level which would mean to excavate roughly 22feet (10'existing + 10-12' new). Furthermore, there is going to be 2-story addition to the existing condition. Independent steel structure from the basement level. But we are not EOR on this project, we were hired to design SOE...The ground water was found 30' below the sidewalk level..I guess can have a small bobcat on site or small drilling rig..What more information would you need in order to elaborate this problem more? Thank you.

RE: Sheet Piling

(OP)
And picture of a boring log

RE: Sheet Piling

(OP)
PEinc - Thanks! I know what can happen that's why I am trying to find the best solution/answer not to let it happen..

RE: Sheet Piling

In my opinion, the safest way to do your job economically is to underpin the adjacent buildings and install sheeting where there are no buildings or where they are far enough away to be of little concern. If you are going deeper than about 12' or 13' below the adjacent grades or about 10' below the existing, adjacent basement or cellar floors, you probably will need either tieback anchors or internal bracing (either cross bracing or inclined raker braces). If the new foundation walls are not or cannot be designed to support the lateral earth and surcharge pressures, you will need permanent tieback anchors. For using either temporary or permanent tiebacks, you will need to obtain underground easements. This might be difficult, especially if using permanent anchors.

Some of the other, above-described, support methods might work fine under the right ground conditions and with qualified and available contractors. I personally do not design structures that might work. Usually, underpinning will have the least effect on reducing the usable area of the basement/cellar, which I often see as the biggest concern with owners and their architects and structural engineers. As long as the water table is below the bottom of your proposed foundations (as you indicated), you will probably find more contractors interested in bidding conventional, concrete pit underpinning and sheeting than the other methods. I would definitely not support the adjacent buildings with soil nailing or with steel sheet piling unless my client insisted and also gave me a strongly written indemnification agreement, and even then, I still might not do the design.

www.PeirceEngineering.com

RE: Sheet Piling

Couldn't agree more, PEinc, especially with "support methods might work fine under the right ground conditions and with qualified and available contractors". I would only add "and with an experienced and qualified geotechnical designer".

The suggestion I made regarding Munich-type walls was to present a solution that is typical in this area and that performs well in the typical waterless CDG ground conditions, even close to buildings. However, if there isn't an experienced contractor available who dominates the technique and doesn't have enough accumulated experience, this solution should be avoided and underpinning would be the best option.

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