Thread: Slab-on-Grade Engineering Required?

After years of reading the IRC deferring to the IBC deferring to PTI and looping around endlessly, interrupted only here and there by exceptions allowing the building official to decide this and that, I still cannot make an air-tight argument that a slab-on-grade in expansive soil must be:

(1) designed by an engineer or "design professional"

(2) inspected by that engineer during the process

While I'm at it, how about soil testing to proceed the construction of the above foundation? PTI says that soil testing "shall" occur. IRC and IBC say that you must adhere to PTI requirements, but then say the building official can decide.

Jeez! Any ideas here?

Thanks,

Aaron

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Part of a soils test is to determine the bearing capacity of the soil. The engineer must know the soil bearing capacity in order to design the footings.

Originally Posted by Aaron Miller

After years of reading the IRC deferring to the IBC deferring to PTI and looping around endlessly, interrupted only here and there by exceptions allowing the building official to decide this and that, I still cannot make an air-tight argument that a slab-on-grade in expansive soil must be:

(1) designed by an engineer or "design professional"

(2) inspected by that engineer during the process

While I'm at it, how about soil testing to proceed the construction of the above foundation? PTI says that soil testing "shall" occur. IRC and IBC say that you must adhere to PTI requirements, but then say the building official can decide.

Jeez! Any ideas here?

Thanks,

Aaron

Aaron, I always have read into the IRC the same as you (follow the Post Tension Institute recommendations).

Where the PTI states 'SHALL', I take this to mean that THERE IS NO OPTION-- shall means you 'will' to it this way.

So, when the IRC refers to the PTI (that says that soil testing *shall* occur), that means that the IRC is defering the to tighter/ higher demand.

One is not allowed to do a post tension slab *without* engineering. Period.

But was that the question you were asking?

I think this answers the question *I* thought you were asking.

From the IRC (underlining and bold are mine)
- R401.4.2 Compressible or shifting soil. Instead of a complete geotechnical evaluation, when top or subsoils are compressible or shifting, they shall be removed to a depth and width sufficient to assure stable moisture content in each active zone and shall not be used as fill or stabilized within each active zone by chemical, dewatering or presaturation.

In other words, one *can* have the geotechnical testing and following engineering done to design a slab sufficient to withstand movement caused by the soil, but, *IF* one *is not* going to do any soil testing and engineering, one SHALL remove that soil to a depth and width sufficient to assure ... blah-blah-blah.

Originally Posted by Jerry Peck

One is not allowed to do a post tension slab *without* engineering. Period.

But was that the question you were asking?

I think this answers the question *I* thought you were asking.

From the IRC (underlining and bold are mine)
- R401.4.2 Compressible or shifting soil. Instead of a complete geotechnical evaluation, when top or subsoils are compressible or shifting, they shall be removed to a depth and width sufficient to assure stable moisture content in each active zone and shall not be used as fill or stabilized within each active zone by chemical, dewatering or presaturation.

In other words, one *can* have the geotechnical testing and following engineering done to design a slab sufficient to withstand movement caused by the soil, but, *IF* one *is not* going to do any soil testing and engineering, one SHALL remove that soil to a depth and width sufficient to assure ... blah-blah-blah.

JP:

Good point.

Thanks,

Aaron