Rubble stone foundation underpinning project planning (overview)

[jpyeron]

Please bear with me, as I have never managed an underpinning project before. My goals today are to obtain/confirm the high level steps so I may ask more detailed/accurate questions later.

Here is my outline of tasks:

1. Define depth required to accommodate future use
2. Survey site
2.1. Existing Foundation
2.1.1. What about it?
2.2. Building in general
2.2.1. What about it?
2.3. Soil?
2.4. Anything else?
3. Draft plan & sequence activities
4. Construction


What am I missing or have wrong?

 

[SirAl]

Underpinning, to me, implies that there is an existing foundation requiring additional support to fix a problem or to carry additional load. Perhaps start with defining what the underpinning is to provide and, if known, summarize the soil conditions inherent to the site.

 

[PSlem]

You will probably be doing concrete pit underpinning. It may be necessary to first excavate under the footing and form and pour a slab to prevent rubble falling out. Some questions: What is size, spacing, and sequencing of pits? Is water going to be a problem? The pits will have to be shored as you excavate along with an access pit in the front. What are details? Will clay spades be required? Will spoil be removed with buckets and a pulley? If excavation is planned adjacent to shoring, will waterstops be required? Is continuous or partial underpinning required? Will temporary walkways for public be required?

 

[PEinc]

PSlem mentioned several important considerations. There are many other considerations. Rubble stone foundation? Column footings? Adjacent excavation required? Lateral support for underpinning? Permanent or temporary lateral support? Confined space entry precautions? pre-construction building survey? Survey monitoring during underpinning?

Read the underpinning chapters in books by Winterkorn & Fang, Robert Ratay, and Alan McNabb.

http://www.PeirceEngineering.com

 

[oldestguy]

Also, what is the condition of the foundation? Will it require grouting to solidify it?

Monitoring the building elevations may be needed to be sure nothing settles in the process.

A guarantee from the contractor to be sure his work does the job.

Who draws up the plans for the work? Is that person insured for errors and omissions?

 

[paddingtongreen]

The first step is to define the project, what is to be achieved? I am not sure you are using "underpinning" to mean the same as I would.

Michael.
Timing has a lot to do with the outcome of a rain dance.

 

[jpyeron]

PEinc: Books in specific? I looked on Amazon, but there were many by the first two and none by Alan McNabb.

 

[jpyeron]

updated outline

Rubble stone foundation underpinning project to provide deeper basement
Project specific #’s in []
1. Define interior depth required to accommodate future use [11’ 4”]
2. Survey site
2.1. Soil conditions
2.1.1. Type [clay]
2.1.2. Frost line @ X [2’ 6”]
2.1.3. What else?
2.2. Existing Foundation
2.2.1. Height [6’]
2.2.2. Depth below grade [4’]
2.2.3. Wall boundaries [2 exterior, 1 party]
2.2.4. Re-grouting? How to determine?
2.2.5. What else?
2.3. Building in general
2.3.1. Pre-construction survey
2.3.1.1. Water issues? [receives water from party wall when rains]
2.3.1.2. What else?
2.3.2. What about it?
2.4. Anything else?
3. Draft plan & sequence activities
3.1. Pit size
3.2. Lateral support
4. Construction
4.1. Monitoring
4.1.1. Elevations for settling
4.1.2. Anything else?

 

[jpyeron]

I moved the books sub topic to a new thread (here)

 

[oldestguy]

What else?
Well, in constructing the blocks of underpinning concrete how are you tying them together? How is load transferred down to the underpinning?

A common way is to drive re-rods into the earth alongside and below to the next block zones. This makes digging difficult for the neighboring blocks,but not impossible if the rods can be bent and then straightened.

Once the concrete is hardened and partly filling the cavity, we have then rammed a stiff mortar into the void between the concrete below and what ever is above. You might even use an expanding grout to get some load transfer.

If you really want to transfer a decent load, you could install a form of screw jack there to pick up the load before raming in the stiff mortar..

You do know about how concrete will shrink as related to water content, right?

So you see, lacking an experienced person on the job, a good treatise on different forms of underpinning might be a good investment.

 

[PEinc]

With all due respect to oldestguy, the details that he mentioned above are all described in various underpinning books but are rarely needed or used.

I worked for a national, design-build underpinning company and now continue to design major underpinniing jobs for qualified contractors. I have designed and constructed several hundred underpinning jobs. I never used dowels or reinforcing steel in underpinning piers, never used non-shrink or expanding grout for dry packing, and never needed to use a jack to transfer loads to the piers. Most of a pier's concrete shrinkage occurs before the pier is dry packed and there is insignificant shrinkage in 2 or 3 inches of dry pack. Properly installed dry packing can transfer load to an underpinning pier. I have used keyways between underpinning piers but only when forced to by one local structural engineer.

www.PeirceEngineering.com

 

[oldestguy]

PEinc. Nice going. Appears to have gone fine.

All I can say is with much fewer jobs, that's the way I did it.

 

[PEinc]

oldestguy, you aren't alone by any stretch. You made some very common underpinning comments. I've been arguing (I mean "discussing") them with some engineers for 29 years.

www.PeirceEngineering.com