Water Tower foundation design 1

[Scotto]

Problem: Rusty geotech skills :-(

Question: Looking for current state of the practice on analysis and evaluation of foundations for a water tower (ring foundation and/or raft)

Desired result of posting: Better understanding of most common and/or most effective approaches to this type of foundation analysis. Ideally, a worked example (that has been successful) or suggestions on where to go.

Thanx!

 

[Ron]

Scotto...not sure where you are located, but here in the Southeast US, most common for small towers such as this is raft (mat) foundation.

 

[ishvaaag]

Since the loads are important, even pile-raft foundations wouldn't be out of consideration, I think. This appeals to common sense in stability.

 

[benishak]

Ring foundation comprising of circular base slab and ringwall should be most efective one. The most optimum approach is to analyze using FE to most economical results. Windload/Seismic will govern most cases when the tank is empty/full.

 

[Scotto]

Ron, ishavaag and benishak,

Thanx for the courtesy of a reply to my post. This helps to validate my approach and build a bit more confidence. I look forward to rejuvenating my geotech skills through the input of those more experienced than I.

 

[larssun]

Assuming a ring-wall foundation for a 75,000 gal (100 ft tall x 20 ft diameter) single pedestal spheroid Water Tower on clayey soils:

How deep should the borings be specified to conservatively evaluate foundation bearing pressure, differential settlement, lateral pressures and compaction requirements?

What tests beside blow counts are recommended?

Thanx,

larssun

 

[ishvaaag]

I would say with 25 m or so you will have seen most of what concerns to short term settlement, but get as much you can afford in order to have the best assessment.

For clays, one way or another you need to establish the shear strength, for proper design of piles if any. The OCR ratio and limits are also required for proper assesment of the settlements.

And make your foundation as deep and wide as you can to avoid tilt problems from eccentrical P-Delta loading or iterated prevalent loading form wind.

 

[ayfarm]

I would consider individual pile/ftg. foundation also.