Ground bearing garage floor with medium to high heave potential 2

[Aussie Dave]

On a job I am working there is a number of garages that need to be built. The site has a clay soil with a medium-high volume change potential between 100-150mm and the ground bearing strength of the soil is 80-100KN/m^2. I was going to design a ground bearing slab 150mm thick with 150mm sub base. Because of the heave potential I was going to use either an A252 mesh 50mm cover from top of slab or place the A252 mesh centrally. But because of the heave potential I am not sure if I should use a block and beam floor instead what does everyone else think ?

 

[BAretired]

How big are the garages...one car, two cars or multi cars? Can you tolerate a 150 mm heave?

BA

 

[oldestguy]

If concern is big, think about laying garage slabs on insulation. If untra concerned, also surround them with a buried 4' wide insulation buried some. A little goes a long ways.

 

[Aussie Dave]

The garages are either a single garage or some are double garages only, but yes after talking to others in the industry, they are suggesting to stay with my original 150mm slab on 150mm grade, because it is a garage after all.

 

[BAretired]

Insulation would help prevent frost heave, but would not resist heave due to a swelling clay soil. A heave of 100 to 150 mm is likely not acceptable. It may be prudent to use a structural slab with void form under the slab.

BA

 

[oldestguy]

OG here. My post for insulation probably was not applicable, once I read the post again. BA has it right. Another thing to think about. How can you maintain constant moisture content? Certainly don't plant trees nearby.

 

[Ron247]

100-150 mm is 4" to 6" of heave? How much force do they estimate it would take to prevent that much heave? What is the perimeter foundation setting on?

 

[Aussie Dave]

Hi, Thanks for the comments. I have a geology team onsite at present, and they are doing the ground survey for the site, I will not have any real information till the end of the month. But they told me that the previous results to a place opposite my location have a firm to stiff clay and according to the NHBC has a ground bearing strength of 90-100KN/m^2. In the NHBC Chapter 4.2 Table, 7 void dimensions for medium to a high volume change of 100-150mm can be assumed for this site until I get the results at the end of the month from geology. I have also read in the NHBC that a Void former can be used to form a void over clay soil when it swells. I will need to contact some manufacturers with regards to formers. For the garage walls, I have assumed a 600 x 225mm one-meter deep strip foundation with mesh reinforcement in the top and bottom of the foundations with 50mm cover and heave protection; this is all speculative until I get the results back from geology and there are no force calculations currently done.

 

[Aussie Dave]

I have been in contact with a manufacturer of clay boards, and they are saying that clay boards can deform to make cavities of up to 160mm for situations such as my site with heave issues of 100-150mm. Has anyone used these before for similar circumstances?