Design Loads for Concrete Liners in Shafts

[jarhead76]

Hello,

I'm looking for references on design loads for concrete liners in deep shafts. We are doing preliminary design for an 800 foot deep shaft. Site sub-surface exploration has not been completed yet. We are considering using a concrete liner as the permanent lining. I'm interested in determining the external pressures so that I can design the lining. I've checked USACE EM 1110-2-2901 and a few textbooks, but haven't found any real good direction yet.

Could anybody point me to a good reference?

Thanks!

 

[miningman]

800 feet is not deep , it is in fact quite shallow. Cant give you references for design manuals but you'll almost certainly end up with a concrete thickness of 2-3 feet.

Major practical issues are is this soft rock or hard rock country?? Expected water inflow rates?? Grouting required yes or no ??? Is this a mine or civil engineering project. Expect totally different standards

 

[jarhead76]

Thanks miningman,

This is a civil engineering project in the NE United States. We haven't started our sub-surface exploration yet, so I don't have detailed geotech info for you. I can say that we expect the shaft to be located in a shale formation and that grouting will be required.

Our preliminary estimates of the shaft lining thickness are on the low end of the range you suggest, but it really depends on the assumptions you make regarding ground water pressures. This is why I was looking for some design references, I wanted to get a sense for some reasonable design criteria. As the shaft OD, and thus project footprint and cost, will be directly tied to the lining thickness, we really want to nail this down as early on in the process as possible.

Thanks again.

 

[miningman]

OK, now I'm curious. Is the shaft to be excavated with drill and blast techniques or some form of raise boring?? What is the presently planned inside finished diameter??

Regardless, in shale I would expect semi significant overbreak ( possibly extensive if using D+B) and the fact that you anticipate grouting means there'll be close to 350 psi hydrostatic pressure at the bottom of the shaft.

The local in situ stresses may help calculate overbreak but I would doubt the accuracy of any such calculations.... in my opinion 800 feet is too shallow for these calculations to provided usefull data

 

[jarhead76]

Shaft will be D&B. Finished ID is 28 ft.

The potential for 350 psi at the bottom of the shaft is exactly what I am concerned about. If full hydrostatic is actually acting on the concrete lining, then we will need to almost double the thickness of the lining we are carrying through preliminary design.

 

[miningman]

Well for what its worth, I'm a kinda practical, hands on, field type of engineer rather than a by the book, theoretical guy and I certainly couldn't do the required calculations but I'll predict that from what you've posted, you'll end up with at least 3 feet of concrete thickness , and you WILL have 320 psi at the bottom of the shaft. 28 feet is a bit larger than anything Ive sunk so it may end up being 4 feet and the overbreak will provide something like 25-33% increase in actual concrte volume.

This is starting to be a big hole!!!!!!!!