Replies

1. 
   quicksilver | Apr 28, 2008 06:37pm | #1

   Christ, I can't believe I spelled 'underpinning' wrong! :)

2. 
   jrnbj | Apr 28, 2008 09:32pm | #2

   9 feet!!!!
   that's not underpinning, that's excavating a sub-basement ;-)
   How's the great state of Md. these days?

1. 
   quicksilver | Apr 28, 2008 10:19pm | #3

   My first inclination was that it was like mining. I live in DC now. Md. and Va suburbs seem to be real slow. The remodeling market is picking up in the city, but a lot a free lancers are making it tough.

3. 
   BungalowJeff | Apr 28, 2008 10:44pm | #4

   It will depend on the set of drawings from the engineer. This is done in Manhattan all of the rime (deeper) as real estate prices soared, retail businesses built down to add space.

   ...that's not a mistake, it's rustic

1. 
   quicksilver | Apr 29, 2008 12:39am | #5

   Any Idea of what techniques are being used? Like I said the engineer's drawing shows only ABC sequencing and the architects section show just the finished wall with the footing.

1. 
   BungalowJeff | Apr 29, 2008 07:52pm | #7

   Too many variables. Soil type, groundwater level, existing foundation type/condition, framing, etc. to guess at the details. If it is not blatantly clear from the structural drawings, then bug the engineer until the details and sequence are crystal clear.

   I would guess that 8' would require two rounds of excavation and underpinning. I have not heard the ABC reference before, so I may be missing something obvious.

    ...that's not a mistake, it's rustic

1. 
   quicksilver | Apr 29, 2008 11:19pm | #8

   Thanks for replying - you and everyone who did. I agree that there is not enough info from the structural plans - in fact I have not seen them yet. What I know has been from word of mouth - in that case to use the word 'know' is a little strong. The ABC sequence is basically dig one, skip two. The building is an old city supermarket. The existing footing is a basic poured concrete footing probably poured 50 or 60 years ago. The existing footing will be sheared off after dry packing. What I was looking for was an approach to the excavation. My thoughts were if I was to leave 4 feet of soil around the perimeter and the excavate down five feet from the center I could get a mini excavator down their and dig in perpendicular to the wall shore the sides and then dig down the last 4 feet. Or do I just lay out a 4' (along the footing) X 5' (perdendicular to the footing) and dig straight down. I used to be construction manager for the architectural firm that is doing the building. So I have experience with them and this is why I was putting time into this without seeing the structural drawings. I was working at an estimate that was getting to be close to two hundred grand and I realize that I just won't be able to compete and frankly started thinking -do I really want to take this on? Things are a little slow but they are picking up. So no, a potential nightmare isn't going to help anything. So thanks for your replies. I can still take on the rest of the carpentry.quicksilver

1. 
   BungalowJeff | Apr 30, 2008 04:19pm | #9

   Well, I think you have the right atttitude and a proper inkling to make your decision on bidding it. Many stone party wall foundations are wrecked in NYC by contractors ignoring plans, or not even getting an engineer involved. That is, until 50 feet of exposed rubble party wall collapses.

   Good luck with your choice.

   ...that's not a mistake, it's rustic

   Edited 4/30/2008 9:19 am ET by BungalowJeff

2. 
   dirtyturk | Apr 30, 2008 05:35pm | #10

   Just picked up on your question. Did a project about 20years ago that underpinned an existing basement which faced on a steeep hill and was about 250ft. long.

   First off, do you have working space around the perimeter for your equipment? (We had already cut into the hillside for the new basement extension so that wasn't an issue).  Another thought came to mind as I wrote this.  Are you working from the inside?

   Second, is the existing wall stable as in no cracks or unusual settling? Verify this beforehand and document it with the engineer or owner...or you'll be blamed for any 'damage' that, of course, you caused.

   Third, verify exactly what the engineer is looking for as far as reinforcement and the finish on the inside face. If they're going down 9ft then the question I would have is the intended purpose of the inside. Basement?  And how do they intend to excavate under the existing floor slab? Or do they? I've heard of engineers demanding a smooth vertical surfaces.  (Just cause we can draw it doesn't mean that it can be done...unless you gotsss lottsss of money!).

   The ABC sequence is the most common, straightforward and safest method of doing an underpinning.  We dug out 4ft, left 8ft, perpendicular to the wall and down.  We were also looking for mass so the cut went inside a foot from the existing footer , if memory serves me correctly, and formed out to about even with the existing concrete on the outside. BIG Lump under there! Since you've got  to trim off the existing pad it sounds like there is some unspoken use here. (A thought. Are the walls on a property line or close enough that the foundation has to be cut/trimmed off?)

   All that having been said, the current pricing on underpinning a wall around here, Northern Ohio, is at or about $1000.00 a linear foot.  Seems like a lot but we are talking about a very labor intensive project and a dangerous one which extends the time to completion.  Yes, there are those around here (free-lancers exists everywhere) who will underbid anything so really hitting your contact with detailed information requests will make them aware of your thoroughness. (Gets my attention)  Reassures them that you'll get it done. Most free-lancers don't ask questions just hand over a low ball bid that gets attention, which the Owner pays for after the fact.

   Enough already. Hope this helped.

   ciao, ted

3. 
   quicksilver | May 01, 2008 04:04am | #11

   Thanks for the advice. There is room for the equipment. Everything will take place from inside the building (that is typical in the city). There is enough room to get a small excavator and a small Case loader in there. Plan of attack will be at least at this point is to leave a four foot perimeter of dirt at present grade all the way around the building by removing the dirt from the center and take it down four or five feet. I am not sure at this point how far OSHA will let me dig before I have to shore. Then I should be able to put the mini back hoe perpendicular to the building and peel off the first four foot increments into the center where the loader will be able to come into play. Once I get to the new grade I can use the mini hoe to dig down and under the foundation as much as it will go with the machine. The I'll finish it up with hand labor. Sound OK. At least a plan is coming into focus. So now I am now considering the project again after talking today top the project manager. The thousand a linear foot is interesting. After seeing this I checked my estimate and I was coming up at $931/foot. If I bid which I'll decide this week I'm going to go with the $1000/ft. Thanks a lot.

4. 
   dirtyturk | May 01, 2008 10:42pm | #12

   "I am not sure at this point how far OSHA will let me dig before I have to shore."

   You might want to consider pointing out to the Project Manager that if OSHA comes in and dictates an extensive shoring requirement (beyond what you have already thought about) that you will need to pass the cost on, and of course you'll be fair about it but.....

   Usually the soil conditions dictate the depth and width of an excavation like this.  I have seen hard clay without any fines that could hold up without shoring down to 10'0", and others that can't stand after a two foot dig.  OSHA does take this into consideration, most times.  Still 9ft down and 4feet width? Gonna have to watch yourself.  That and you may be working hard to get below a fill under that slab from when the building was built. 

   (If you do find Jimmy Hoffa down there make sure to call the National Enquirer first!  They'll pay for the pictures and interview.  Of course if you find that bag of gold coins I dropped....well, I'll pay a reward.  ;}  )

   Good luck on the Bid! Hope you make tons of money!

   ciao, ted

5. 
   segundo | May 02, 2008 03:13am | #13

   its been a while since my last training, but i still have a competent person card for excavation and shoring.

   depending on the type of soil, and that should be classified by a third party, there are strict rules as to exactly how to slope or shore an excavation.

   you shouldn't be worrying about what OSHA is going to make you do, you should be coming up with a plan that will ensure that no person is in any way shape or form going to be in harms way.

   even a 3 foot deep trench can break bones if it caves, a trench that is up to your shoulders can kill you even with your head still out, by suffocation while your co-workers are digging

   if you have shored an excavation and for some reason or other it needs to be redone or reworked, watch out. rework is where the worst accidents happen.

   you might want to consider pointing out to the project manager that you both need to have a specific plan and the training required to go forward with this project. it is common to have safety training periodically for something you do all the time, a new or unfamiliar area be specifically addressed. talk to some safety people, and yet once again i would start with the people at american pile driving equipment inc and ask them who would be a good person to conduct competent person training for this project.

   a shortcut here, and an accident will be something you carry with you for all your life, and no amount of money is worth it.

6. 
   dirtyturk | May 02, 2008 03:42pm | #14

   I agree completely with your assessment of the requirements for any excavation!

   About once or twice an excavation season we read about a trench collapse and all of the usual stories about how the shoring or safety was minimal or, gulp, ignored.

   I have shut down an excavation or two because someone was being extremely stupid or down right arrogant about the potential dangers.  Knock on wood that I have never had a serious problem occur and intend to keep it that way.

   I didn't know that you can get carded to be the person to determine the safety of excavation and shoring. Learn something every day.

   ciao, ted

7. 
   segundo | May 03, 2008 06:57pm | #15

   well its not a big deal to get a card, it basically just says that you attended instruction by a safety professional, and that you are a competent person.

   OSHA says that among other things a competent person is one that has the knowledge to do the work correctly, and the ability to stop the work when he/she sees something that doesn't look/feel right.

   i called OSHA once, when as a superintendent, i wanted to make sure that we had all the training and procedures in place including documentation (covering my butt) for working out of suspended baskets. The very helpfull and practical OSHA person i talked to told me my crew didn't have to have documentation of training, as long as they knew what they were doing (competent) and that anyone involved would be free to say "hey, thats not right, we need to make it better by doing this" or "stop"

   as the leader of a crew i always try to involve everyone, and make sure that everyone knows the most important thing to do is make sure, and feel comfortable to ask questions if your not sure, that everything is safe. when the crew is polled, and no-one can find anything wrong or shaky even, i feel much better.

   i suggested sheets and shoring from the beginning, OSHA may not require that much, but i know that by using that method correctly it will be plenty safe. gambling with money in business is one thing, safety should never be a gamble.

     

4. 
   segundo | Apr 29, 2008 03:46am | #6

   are you asking if you are required to excavate beneath an existing structure, and then form and pour structural concrete?

   is this a continious structural wall and footing, or is it just sections or "piers"?

   as another poster suggested in major urban areas it is fairly common to "retrofit" foundations, and there are many different techniques for doing this, but from your question it sounds like you are required to excavate....

   sheet piles, and structural shoring to prevent excavation from caving in and to temporarily support structure while "retrofit" its foundation.

   this is a similar technique to what they used on the "Big Dig" although not on as big of a scale. also called a "coffer damn".

   it is fairly straightforward, but also very specialized. i would think about subcontracting the 1. sheet piles, 2. structural shoring and welding, and then 3. the removal of temporary structural shoring as the reinforced concrete structure is at a grade and strength to allow it. 

   it requires skill and experience with 1. heavy equipment (crane, excavators, and trucks) as well as 2. metal working skills (cutting to size, fitting, and welding) the layout skills transfer over from craft to craft and most importantly 3. a thorough understanding of the process and proper sequencing of events to maximize efficiency. if you don't know what you are doing, and rely on subs to know and they are not as good as they sounded like they would be....

   if you are still considering this undertaking, if i was you the first people i would contact would be American Piledriving Equipment Inc. for an evaluation of the equipment required. if you are going to be driving sheet piles you want one of APE's vibro's, and their advice on how to use it.

   http://www.apevibro.com/asp/default.asp