DIY Home Improvement, Remodeling & Repair Forum > DIY Home Improvement > Bricks, Masonry and Concrete > Underpinning Basement Standoff Jacks / Supports For Inside Acess Only?


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Old 01-11-2017, 12:22 AM  
rsvp
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Default Underpinning Basement Standoff Jacks / Supports For Inside Acess Only?

About half of our basement sets on a 16" wide shaped limestone wall held together with mortar from the 1870s. It extends just over 4 feet and sits on undistributed compacted dirt. We are wanting to underpin the wall in this area of the basement to achieve full 8' foot tall walls by digging the existing wall out in 20" wide sections. Each section would first have a 8" x 20" x 16" reinforced concrete footer placed on the bottom. On top of this would be placed a reinforced 2 cement block wide and deep column which will be filled with cement. The remaining gap between the existing limestone wall and the block underpinning would be filled with expanding concrete.


As a extra safety precaution I'd lid to use a temporary brace under the section of limestone wall section from which the dirt will be removed. Based upon years of driving forklift this could easily be accomplished by placing a single forklift fork under the wall section with an additional extension added to the fork to provide access (cribbing would of course be placed under the fork since hydraulics do fail). Using an actual forklift is; however, not an option due to cost and access issues.


I've looked at foundation jacks; which are essentially piles with a "L" shaped lifting shelf attached to them; however, they are not an option as they are placed on the outside of the foundation and because they would provide no working access if placed inside. The shelf used on these jacks are also too shallow as we want support to extend under the full width of the wall.


I've previously experience building our own four car garage and attached shop by hand including digging the foundation and basement entrance by hand. Its been over 10 years and no cracks, even in the sidewall, as build stuff to last and do the proper research beforehand.


Anyone aware of a jack or lift that might work for such a situation. I've not quite found anything to date. About the only thing that might come close is a manual scissors pallet with an extension placed on one of the forks; however, one might have problems with finding the right fork and the fork would need to be able to support around 4,000 pounds as each section of limestone would weigh around 1,500 pounds. Of course each section of the wall is partially supported by neighboring wall sections but its better to be safe than sorry and one needs to account for the amount of leverage caused by focal point.



Last edited by rsvp; 01-11-2017 at 08:57 PM.
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Old 01-11-2017, 01:35 PM  
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Welcome to the site. Can you post photos of the wall.


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Old 01-11-2017, 02:05 PM  
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My first thought is jack up the house and rebuild a whole new foundation. Why do you want to preserve the old foundation?
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Old 01-11-2017, 08:05 PM  
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My first thought is jack up the house and rebuild a whole new foundation. Why do you want to preserve the old foundation?
One half of the house sits on 18" thick limestone foundation that is full height. The other half is of the same construction wall, but extends just over 4 feet to be below the frost line. The existing wall is massive, solid, and has never leaked unlike many modern walls which use hollow blocks.

There is no reason to replace the existing foundation when underpinning would do. The new basement entrance we put in, which connects to our attached garage/shop, is made from a group of older 3 chamber cement blocks recycled from a barn, which are reinforced in rebar and filled in with cement. Cement blocks with a footer would be the easiest method to complete based upon previous experience as the process could be completed in steps at any time.

The only question is developing a temporary adjustable height moveable brace as an extra precaution.
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Old 01-11-2017, 08:55 PM  
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Welcome to the site. Can you post photos of the wall.
We live in an area whereas the base ground layer under any dirt is limestone. Older houses are built with pieces of limestone taken from the ground and roughly shaped into rectangles and square of various sizes which are then joined together with mortar. This is not the finely polished blocks you see in say a county courthouse; however, nor is it a unstable rubble wall consisting of rounded field rocks simply stacked on top of each other.

Here is a quick illustration. The pattern seen on the limestone is a generic adobe illustrator pattern and not actually how it appears - its a series of roughly squared blocks of various sizes which are mortared together.

The plan here is so dig out 20" or so wide sections and to lay a 8" deep footer. On top of each footer is placed a cement block column that is 2 blocks wide and deep. The footers are tied into each other with rebar. Each column is ted to the footer with rebar. The columns will be filled with cement and reinforced with rebar.

The underside of the existing limestone wall is not perfectly horizontal thus the gap between the blocks and limestone wall will vary. What we are looking for is a jack or lift to place under the section of limestone wall above the column we are currently wanting to install. This jack support should contact the underside of the limestone wall at one or two points in a similar fashion to a forklift. It needs to extends the full width of the 18" wall, with any vertical bracing being positioned inside the basement and standing off from the interior of the wall to provide access to the wall.

The final gap between the limestone wall and block columns will be filled with expanding cement in two steps. First, areas around the jack support will be filled, but not quite touch the jack supports under the wall. The jack supports will be removed once that cement is cured and the unfilled areas where the jack supports were will be filled.

I am looking for a safe methodical approach here. Currently the areas where the blocks are shown is composed of undisturbed compacted earth which partially extends into the basement as a series of flat top earthen embankments covered with a thin coating of cement. The top of each embankment is around 18" with a wider base. The top "shelf" was used to store canning jars and other goods back in the day.



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Old 01-11-2017, 09:05 PM  
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We live in an area whereas the base ground layer under any dirt is limestone. Older houses are built with pieces of limestone taken from the ground and roughly shaped into rectangles and square of various sizes which are then joined together with mortar. This is not the finely polished blocks you see in say a county courthouse; however, nor is it a unstable rubble wall consisting of rounded field rocks simply stacked on top of each other.




So you will be digging down on both sides of the wall?
You are concerned about the blocks falling while you are working under there?
Would the stone be big enough to be one block reaching inside to outside?
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Old 01-12-2017, 12:05 AM  
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So you will be digging down on both sides of the wall?
You are concerned about the blocks falling while you are working under there?
Would the stone be big enough to be one block reaching inside to outside?
Here's a better illustration of what we are looking for in terms of a jack.

1. Remove a 20" wide top portion of the cement over the dirt to expose the bottom of the limestone wall.

2. Drill one or two holes in the dirt under the bottom of the wall.

3. Insert horizontal jack arms in the hole or holes.

4. Raise the arms using the jack.

5. Remove a 20" wide column of dirt.

6. Insert cement footer.

7. Build block column.

8. Fill in most of the gap between the underside of the limestone wall and the top of the block wall. This will require temporary spacer wood to be placed next to the horizontal jack arms so they are not cemented into the wall.

9. Remove jack arms.

10. Remove temporary wood spacers.

11. Fill in the remaining space or spaces where the jack arms or arms were.

12. Repeat the process for the next section.

In regards to your questions:

We will digging from the inside only.

Yes, we are concerned about the bottom of wall giving way.

The limestone is of various sizes and are fit together like a 3D puzzle held together with mortar. There are no stones which would span the entire depth of the wall. There are no stones which would span the width of area to be excavated.


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Old 01-12-2017, 12:21 AM  
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I understood all of that, Weight dissipates from the load into concrete at a 45* angle so compacted dirt would have to be more like 60* well into the area where your jack apprentice is sitting.
A fork lift uses weight and leverage to lift a load. Have you considered the weight you will be putting on the foot print of that jack if you could get enough weight to counter the weight you are holding.
The one way you could get the balance is to prop back to the wall but that would be adding stress to the wall that you are holding.
Are you open to other ideas?
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Old 01-12-2017, 01:14 AM  
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To be clear: if I understand the premise correctly, you will not be lifting the wall so much as digging additional basement space below it and adding a block wall (built in small sections) underneath at the new depth. And you want to do this all from the inside. Do I have this right?
I'm only trying to get a clearer picture of the project because it is sort of intriguing.
have you calculated any loads for each section?
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Old 01-12-2017, 01:45 AM  
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I understood all of that, Weight dissipates from the load into concrete at a 45* angle so compacted dirt would have to be more like 60* well into the area where your jack apprentice is sitting.
A fork lift uses weight and leverage to lift a load. Have you considered the weight you will be putting on the foot print of that jack if you could get enough weight to counter the weight you are holding.
The one way you could get the balance is to prop back to the wall but that would be adding stress to the wall that you are holding.
Are you open to other ideas?
The illustration is just a quick mock-up of of how a jack would need to be positioned and not anything I've actually built. The actual jack would need a lot of extra support such as more extensive frame connected, a wider support base, and some type of counterweight.

A 20" x 16" x 48" section of the wall at 169.2 pounds per square foot of limestone weighs in at 1,504 pounds. Any of the gas powered forklifts I've driven in the past could do this easily with a fork extension; however, that not really an option.

Essentially what the original builders did in the 1870s was dig out a pan shaped depression in the dirt inside the basement for a root cellar and cover it with a cement-like layer. The dirt below the cement is undisturbed and still compacted from the thousands of years it has sat there. The floor in this area is only about 2" deep in this area as its essentially the same skim coat they placed on the walls.


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