Helical piers

[Quinta]

Our country club foundation and slab has had significant movement to the point that we will be demolishing and rebuilding our clubhouse. Soils testing at multiple location revealed the existance of "blown, sandy soil to a depth of 150 feet". We did not encounter bedrock or clay."

Question: Would helical piers used in conjunction with a structural slab be a solution that would eliminate future movement?

Are there alternate solutions/technologies?

James Montgomery

 

[rholder98]

What kind of movement was the problem in the first place? Settlement or heave?

There are several things you can do to reduce the effects of active clays. Drilled piers and grade beams will work. A stiffened, waffle-type slab will be cheaper, but will still move--it will just accommodate the movement. It really depends on how much you can tolerate, and what you're willing to spend.

 

[rholder98]

Oops, I just reread the original post--there was no clay. Heave, then, is probably not the problem. Still, piers should help, but proper compaction should, as well. Depending on the soil, ordinary footings could be just as effective, with proper subgrade prep. Did your soils report give you a recommendation for piers?

 

[ArneG]

There are many options in mid to deep foundations such as:

Helical (screw) piers
Geopiers
Steel piles
Concrete caissons
Rock columns
Etc.

Your local geotechnical engineer (the soils testing agency) will be able to recommend the proper system based on local availabilty, past performance in the local soil profiles, local economy, etc.

I've been involved with a couple settlement issues and am suprised that you need to demolish the building.

Typically structures can be stabilized in place.

You should speak with your local geotech engineer and have him give you the options.

 

[bushel3]

Are there many other nearby buidlings. For a country club, I would assume not. If ground vibrations at nearby structures isn't a big concern it may be cheaper to improve the ground using blasting, deep dynamic compaction or another similar ground improvement method. Given that this is a country club, you probably don't need to improve the ground too deep to support the 1 to 3 story building.

 

[grumpa]

Consider hydraulicly driven piers and possibly pressure grouting.

 

[BigH]

Several questions -
(1) you have indicated that the soils testing was done to depths of 150 ft.? Wow, this is pretty deep unless there are other circumstances that we are unaware. Is your clubhouse on 'level' land or, like one job I was involved with, does the clubhouse border on a steep slope?
(2) Is there any explanation as to what is "blown, sandy soil"? Are you in Iowa or other locations with known deposits of loess? Loess has a propensity of collapsing upon watering. If so, perhaps, over the years (and I a presuming tha the clubhouse isn't 'new'), the bits of ground/turf watering about the clubhouse there could be some collapse of the loess structure.
(3) How old is your clubhouse - when did the cracking first appear? If it is relatively old, say 15 years as a point of discussion, and the cracking did not appear until recently, then there may be something other than simple "soil incapable of supporting loads without distress" syndrome. You would want to look into environmental changes or physical/operating changes that has taken/is taking place that might be a causative factor.
(4) Is there any standard penetration test "N" values given for the soil stratum in your soils testing report/log? This would lead to descriptions such as loose, compact (or medium dense) or dense being used on the logs - if, in fact, they were. Assuming that you don't have (2), for settlements to occur "N" values would have to be quite low - in the order of 4 or less and, at that, I would be surprised if these settlements wouldn't have occurred soon after construction - if they did, then see (3).

Once these factors have been noted - a rational approach to the best course of action could be developed. If, as you have, indicated, the cracking is substantial rendering the clubhouse non-functional, then replacement may be the best policy. But, you want to know the points above that will lead to the most suitable choice of foundations or ground treatment to use.

Basically, if new loadings are relatively high, use of stiff mat (raft) or grillage style foundations can be considered. Any settlements would be more or less uniform - differential movements minimized.

Deep foundations (shallow piers, driven pipe/timber piles, auger cast-in-place piles, stone columns) could be considered but as mobilization of equipment will be of large initial cost, be sure that this is more appropriate than using raft/mat/grillage or even spread foundations.

Else, you could treat the ground such as via dynamic compaction - but this sets up high stresses and might affect nearby structures (yours or those of others).

The best choice of foundation type would be based on loadings of new structure, the actual support characteristics of the site 'blown, sandy soil' - which, by the way is a very poor engineering description that leads me to ponder about the drilling company (hopefully not an geotechnical drilling company), external constraints.

I would approach a local geotechnical firm - of good reputation - to help you down the path. Doesn't your club have any members that are geotechnical engineers?

 

[fndn]

Based on your description, you may have collapsible soils. Like BigH suggested seek a local firm with good reputation. Also you may drive to the the city or county if unincorporated and look at the soil reports on nearby structures. At the very least you'll get names of local firms, type of soil profile and foundation type selected for use.