Row house basement dig out with underpinning
Row house basement dig out with underpinning
(OP)
We are looking into digging out a basement from about 3 feet of crawl space on our row house that dates from about 1910. Our 3 story building has a rubble stone foundation and is “attached” on both sides to other 3 story houses. Both neighbors have crawl spaces too. In parallel to coming to this site for preliminary technical advice, I am talking to real estate agents to gauge the value of such work.
I am an architect, no wise cracks please :) , and I have a lot of experience working on these types of homes. A knowledgeable and competent general contractor with whom I have worked with on a few different jobs in the past has indicated that he would like to take this on. He does not have any experience in underpinning structures, no wise cracks please :)
I have read on this site, on multiple occasions, that one should only use an experienced underpinning contractor. However, if I hire a structural engineer who has experience in underpinning structures and both he and I follow the contractor closely, is this feasible?
Any advice on choosing a structural engineer? Any suggestions in Montreal Quebec Canada?
I will also see what the best known underpinning turn key contractors can offer me. I will look into which structural engineering consultants these specialized contractors use - I know these companies mostly sub out this consulting work)
I would also love to see some properly executed drawings for this type of work – any offers?
And, of course, any other suggestions / comments would be welcome!
Thanks.
I am an architect, no wise cracks please :) , and I have a lot of experience working on these types of homes. A knowledgeable and competent general contractor with whom I have worked with on a few different jobs in the past has indicated that he would like to take this on. He does not have any experience in underpinning structures, no wise cracks please :)
I have read on this site, on multiple occasions, that one should only use an experienced underpinning contractor. However, if I hire a structural engineer who has experience in underpinning structures and both he and I follow the contractor closely, is this feasible?
Any advice on choosing a structural engineer? Any suggestions in Montreal Quebec Canada?
I will also see what the best known underpinning turn key contractors can offer me. I will look into which structural engineering consultants these specialized contractors use - I know these companies mostly sub out this consulting work)
I would also love to see some properly executed drawings for this type of work – any offers?
And, of course, any other suggestions / comments would be welcome!
Thanks.





RE: Row house basement dig out with underpinning
Without trying to sound rude or arrogant my thought on this would be to not waste anymore time. Barring some miracle type invention, or the inclusion of the other row houses in this construction project, i.e. shore up all buildings attached and build them all a basement, I can't see this working. too many unknowns, too much risk. The engineering fees on this alone make the basement not worth it.
Sorry but that's my opinion,
RE: Row house basement dig out with underpinning
I am posting here to get independent professional advice - good and bad, pro and con.
This project is not uncommon around here, just like in Brooklyn, DC, Philly, etc.
What is normally done is a ramp is dug from the back service alley down to the back of the house and the digging begins…long and painstaking…and as you mention, not without risk
RE: Row house basement dig out with underpinning
I would want to build the new wall inside of the existing rubblestone wall (annoying to lose the floor space I know) but then it would act as a retaining wall for the neighbouring crawlspaces and the existing foundation. It would also make drilling the new piles significantly easier if they aren't trying to install them below existing structure.
I hope it works for you,
RE: Row house basement dig out with underpinning
RE: Row house basement dig out with underpinning
You are correct to involve an Engineer.
Good luck.
RE: Row house basement dig out with underpinning
Anyway... Best of luck! This will not be a small undertaking!
RE: Row house basement dig out with underpinning
www.PeirceEngineering.com
RE: Row house basement dig out with underpinning
PEinc, is was hoping for a reply from you. I watched your presentation on Recent Building Collapses in Philadelphia. I also watched the following presenation: NYC Department of Buildings - An Underpinning Symposium.
Do you know where I can see a proper set of drawings for this type of work?
RE: Row house basement dig out with underpinning
We need to increase the depth of the cellar with around 2.5 meters.
So method statement would be to excavate in sections, dependant of the type of soil between 1 to 2 meters then leave a section then again.
With the reinforcing protruding out on either side (push into soil or bend) then cast the concrete, once you excavate and box the next section the steel is continues. Yes you wil have a vertical dry joint.
With this being a massive waterproofing problem a penetron concrete must be used with a channel and dry skin built on inside of retaining wall and channel between retaining wall and dry skin, channel flows into drain and pumped up to storm water system. Also get a waterproofing specialist to recommend a product for their joints.
This is a costly excercise.
RE: Row house basement dig out with underpinning
We need to increase the depth of the cellar with around 2.5 meters.
So method statement would be to excavate in sections, dependant of the type of soil between 1 to 2 meters then leave a section then again.
With the reinforcing protruding out on either side (push into soil or bend) then cast the concrete, once you excavate and box the next section the steel is continues. Yes you wil have a vertical dry joint.
With this being a massive waterproofing problem a penetron concrete must be used with a channel and dry skin built on inside of retaining wall and channel between retaining wall and dry skin, channel flows into drain and pumped up to storm water system. Also get a waterproofing specialist to recommend a product for their joints.
This is a costly excercise.
RE: Row house basement dig out with underpinning
It would be much easier to understand if you provide a section showing "channel between retaining wall and dry skin"
RE: Row house basement dig out with underpinning
Pit underpinning should not be attempted unless the site has been dewatered to below the bottom of the underpinning pits. Otherwise, you will lose soil while excavating. If you lose soil, there will probably be settlement of the building. It is dangerous to be inside a sheeted underpinning pir when soil has been lost from behind the shoring boards.
There are not many books that show good underpinning details. A couple books that do are:
1. Temporary Structures in Construction, 3rd Edition, Chapter 11, by Robert T. Ratay, Mcgraw-Hill
2. Foundation Engineering Handbook by Winterkorn and Fang, Van Norstrand Reinhold
3. Earth Retention Systems Handbook by Alan Macnab, McGraw-Hill
4. Underpinning by Prentis and White (the "bible" on underpinning) 1950, Columbia University Press
www.PeirceEngineering.com
RE: Row house basement dig out with underpinning
• details in Temporary Structures in Construction by Ratay (although 1st edition)
• details in the free FHWA geotechnical 3-volume underpinning manual online and
• your “recipe” described in this old thread: http://www.eng-tips.com/viewthread.cfm?qid=54204
I now have an idea of how to install and fill a concrete underpinning pier.
Now, more generally, can you help shed some more light on the following:
1. How to start in a row house that has access only via front and back? How to gain entry in a confined crawl space? How to access the foundations in a crawl space?
2. Permanent and/or temporary lateral support options, as required by the unsupported new underpinning foundations
Thanks again.
RE: Row house basement dig out with underpinning
For lateral support of the underpinning, you can extend the piers below the future basement slab. At the top of the underpinning, you still have the original rubble stone foundation wall. This wall and the underpinning need lateral support. You may need to have the front face of the underpinning extend into the basement so that it can eventually overlap the rubble stone wall so that this concrete can be braced by the first floor framing (which may need to be strengthened to support this new axial load from the wall). This is not an easy design because this is a significant deepening of the crawl space to become a basement.
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RE: Row house basement dig out with underpinning
And with a good engineer on board, do you have any thoughts on me using a very good general contractor for this project, with no underpinning experience? (I have worked with him before on numerous occasions and he is competent)
RE: Row house basement dig out with underpinning
I don't know of an underpinning engineer in Canada but ADSC (the International Association of Foundation Drilling) lists InGeo Design, LTD in Toronto as doing geostructural design. Maybe they design underpinning. The Deep Foundations Institute (DFI) lists Petrifond Foundation Company LTD in Montreal as an underpinning contractor. If you call them, they may be able to help you or give you a recommendation.
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RE: Row house basement dig out with underpinning
RE: Row house basement dig out with underpinning
But this is what we normally do it but I would remove the existing floor or atleast part of it.
So see my link below I dont agree to do mass concrete as you are limited on space. Concrete should be a waterproofing concrete as previously mentioned. Not sure on how exactly your wall is placed on the stone foundations but if possible should be removed and placed on new concrete retaing wall. Cause it will probbably fall as you excavate under it any way.
Also you can make the footing of the retaining wall quite large as it forms part of your floor. Channel should be connected to a pipe that goes into your storm water.
If the waterproof concrete is enough I would just go with that so that maintenance can be done on the concrete wall if dry cavity is built one would not be able to see condition of concrete wall.
RE: Row house basement dig out with underpinning
Parrapit, are you building this cantilevered foundation wall in short sections from within a sheeted pit? The new basement will be too deep to just open cut for the new wall. Are you lap splicing or mechanically splicing the horizontal reinforcing steel? Are you drypacking between the top of the new wall and the bottom of the rubble stone wall? With this type of eccentric L-shaped foundation, I would be concerned about the resulting bearing pressure and potential settlement.
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RE: Row house basement dig out with underpinning
I've done it below ground level, no problem. A prison wall no less.
RE: Row house basement dig out with underpinning
I am not as much concerned about injecting the rubble stone as I am about the amount of unshored and unsafe excavation that an inexperiwnced contractor may perform. Construction procredures are probably more critical than the design of the concrete underpinning.
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RE: Row house basement dig out with underpinning
Questions for PEinc and anybody else who wishes to reply:
1. Can you explain the use of louvers? Why not just omit spaces between rows of sheeting?
From Ratay: “It is advisable to use louvered boards at all times to in order to enable backfilling behind the boards where necessary. (Louvered boards are boards placed with spaces left between them which can be packed with sand and salt hay in case the sand starts running after it dries up”
From the online FHWA geotechnical 3-volume manual: “During the placement of the sheeting spaces are often left to permit packing of the soil behind the boards. These spaces are called louvers and are formed by nailing short pieces of wood between the sheeting boards.”
2. From Ratay: “Inserts are installed for an inclined bracing or tieback system”. I am assuming that this is the temporary and perhaps permanent lateral support for the underpinning?? Pls confirm.
I am also assuming that since the top of my existing rubble foundation wall is braced by ground floor framing and the bottom of the new concrete underpinning will be braced by the new slab than it is the joint between these two walls that needs to be braced?
3. And, if I understand correctly, only the sheeting behind the pier will be left behind once the pier is completed – please confirm.
Thanks everybody for reading and contributing.
RE: Row house basement dig out with underpinning
2. The inserts being referred to are embedded steel, usually a piece of steel beam, a t-section, or plate with shear studs. The embedded insert is placed flush with the front face of the underpinning pier. Then, after the piers are finished, you can excavate to the insert and then excavate to subgrade on an angle of about 30 degrees so that raker braces can be attached to the concrete underpinning piers for lateral support. Sometimes the brace is connected to the pier with a plate and expansion anchors. However, if the shear force is too great for a reasonable number and size of expansion anchors, then the embedded insert works nicely.
3. For continuous underpinning piers, the shoring boards between piers may be, and usually are, stripped. A little left-in-place lumber isn't a big problem unless the underpinning is to be the finished wall. In that case, the boards between piers should be stripped. The rear shoring boards always remain in place. The front boards are stripped if the underpinning is the finished wall face or if you need to remove the boards to install tieback anchors or attach raker braces. The front boards may not need to be removed if there will be backfill placed between the underpinning and the new structure in front.
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RE: Row house basement dig out with underpinning
If the rubble stone wall is not very high, it may not need to be braced for sliding and overturning, but the pier probably will need bracing BEFORE you excavate to subgrade and install the new slab. Until the slab is poured, it cannot provide any support to the underpinning. You don't want the underpinning to fall over when you are excavating to the slab grade.
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RE: Row house basement dig out with underpinning
Richard A. Cornelius, P.E.
WWW.amlinereast.com
RE: Row house basement dig out with underpinning
Are you referring to the potential need for a pump, either for a french drain leading to a pit or for a potential bathroom in the new basement?
I did a preliminary check with the city and I think I will not need a pump for a bathroom and may need one for a sump pit.
I also learned from the city that rock is about 11’-0’’ below the level of the crawl space and the water level is around there too – both positive news for this potential project.
Best regards.
RE: Row house basement dig out with underpinning
Richard A. Cornelius, P.E.
WWW.amlinereast.com
RE: Row house basement dig out with underpinning
Does anybody have any practical tips and/or solutions on how to support a rubble stone foundation wall during the pit underpinning process? I am assuming that the 100 year old mortar will not (completely) keep the wall together under gravity.
I cannot see how this support can be removed before the pouring and subsequent drypacking???
Does one leave this support to be cast into the concrete pier and the drypack?
Appreciated,
RE: Row house basement dig out with underpinning
I was thinking that one could use, for each pit, a horizontal metal plate with 2’’x4’’ studs wedged vertically to support the rubble foundation wall above. The plate and the studs would be left to become part of the new foundation.
If so, then one could also use a 4 foot pit instead of the recommended 3 foot pit, reducing the number of required piers by 25% - a significant labour savings. In this case, I would use a plate approximately 2’-6’’ long (parallel to rubble foundation wall) by approximately 18’’ wide.
Please let me know if this makes any sense.
RE: Row house basement dig out with underpinning
www.PeirceEngineering.com
RE: Row house basement dig out with underpinning
RE: Row house basement dig out with underpinning
www.PeirceEngineering.com
RE: Row house basement dig out with underpinning
RE: Row house basement dig out with underpinning
Where can I find the presentation: Underpinning Stone Foundation Walls - Image Results ?
Thanks
RE: Row house basement dig out with underpinning
Option A is preferred by most engineers, most labor intensive
Option B was suggested by several experienced underpinning contractor and at least one engineer endorses this method.
- Pro option B: since half the shared wall is always supported much less risk of stones falling into the underpinning pit, faster / cheaper than option A
- Con option B: shared wall is supported by two different conditions and may be subject to differential settlement; eats up more space than option A
Option C was suggested by an experienced underpinning contractor- Pro option C: faster / cheaper than option B???
- Con option C: eats up more space than option B
Assuming the new wall is designed and sized properly, do you have any more comments and/or opinions on these options?RE: Row house basement dig out with underpinning
The rubble stone wall could fall apart or shear off in Option B.
The surcharge from the existing party wall could overturn the concrete wall in Option C.
Use Option A.
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RE: Row house basement dig out with underpinning
They all should be hand dug and constructed in narrow sections along the existing wall.
They all have about the same amount of excavation and concrete.
There may be a little less drypacking with B.
B and C give smaller basements space which is usually not desired. The row houses already have narrow basements.
Option C has minimal dead load weight (no building load) for resisting overturning and sliding.
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RE: Row house basement dig out with underpinning
EIT
www.HowToEngineer.com