Residential Foundation "Inspections" in Austin TX

[HouseBoy]

Friends of ours have a son in Austin TX looking for a house.(We've known them more than 25 years since our kids were in grade school together and we parents get together regularly still).
I'm very familiar with residential foundation issues due to moisture sensitive clay but around here (Southwest Ohio) those problems are relatively mild compared to Texas and other places. I'm trying to give guidance to them so they know what they are looking at. Ultimately, they will need a good local structural engineer to get their "eyes" on it but in the mean time I'm wondering:
For a house built on a slab foundation around the early 1980's with 3" of differential settlement and drywall cracking throughout some areas of the house, is it likely that the house was not built with a post tensioned slab and is it also likely that undermining or piering is going to be difficult to do well?

I'm just guessing that waffle slabs are more common now but not so common 40 years ago.

I searched for "foundation repair specialists" and I see the same franchise names in Austin that I see around Cincinnati (along with some mom and pop sounding names). I also see some engineering firms that do foundation inspections but as in other places, I'm not sure who is capable, and not tied to a foundation specialty firm too closely (maybe "honest" is another word for that).

Any thoughts?

 

[EireChch]

Are any residential houses built using post tensioned slabs? ever?

Id be wary of a house that settled 75mm differentially. Thats a hell of a lot. You would want to be getting a very good price.

A Texas best geo is probably best to advise! See if you can have a phone call with one, I am sure they will know what is commonly underpinned / repaired.

 

[HouseBoy]

EC
My understanding is that it is common now (in recent decades) in areas where moisture sensitive clay is prevalent and the effects significant.

 

[EireChch]

Thanks HB. News to me.

 

[geotechguy1]

Probably just a semantics thing, and I don't practice in Texas, but it could be differential heave (the soil expanded) rather than differential settlement. A slab can stop evapotranspiration leading to moisture buildup beneath the slab. If the soil beneath the slab is exposed to different changes in moisture content or has significantly different characteristics across the footprint a sizeable amount of heave could occur. Alternatively if it's in a large subdivision it's possible that significant cut to fill earthworks were carried out and the house could be sitting on some poorly placed fill, or bridging across a cut and fill area with significantly different compressibilities. 75mm of foundation settlement caused by foundation loads from a one or two storey stick built house seems pretty unlikely

Ideally find a Texas geotech but if possible, not the one who worked or works for the developer / contractor that did the original earthworks / development. Or maybe find that one, talk to him, but hire someone else.

 

[MTNClimber]

When it comes to expansive soil, it's difficult to know why a structure has moved without knowing how it was constructed. Buildings constructed on drilled piers can still see a lot of movement and damage if not designed or constructed correctly. Additionally the movement could be caused from not maintaining grading to drain water away from the building or if the owner is over-watering the landscaping near the building. There are too many variables at play.

 

[1503-44]

The Balconies Fault passes through Austin, of which there are 100's of associated smaller ones. In fact the area has (one of) the most complex geology in TX. Most faults are just to the west of the city. Moisture is more or less controllable and can usually be remedied, but fault repairs can go on forever. You want to be away from any active faults.

Houses built in the 80's would probably have a simple RC slab. There was some tension slabs being built at that time, but not all that common. Some older properties might have been constructed on CMU piers.

I'd suggest that you try to find a higher resolution map of the known fault lines.

https://escarpmentenv.com/Geologic_map.html

The local office might be able to help.

Natural Resources Conservation Service Offices In Your County
NRCS SERVICE CENTER OFFICE
AUSTIN SERVICE CENTER
1106 CLAYTON LN STE 210E
AUSTIN, TX 78723-1080
(512) 459-1623 ext 3
(844) 496-7073 Fax
Mailing Address:
1106 CLAYTON LN STE 106 E
AUSTIN, TX 78723-1080