Reducing PVR in expansive clay

[oldagpe]

The problem is trying to design a light residential structure on expansive clay, Houston Black Clay. Footprint is 2400 square feet, rectangular, with a wrap-around porch of 6 feet. Area is undisturbed now, no trees or shrubs.

Geotechnical is potential vertical rise of 3.5", ymc 1.25" and yme 2.25" for 2nd edition PTI. Borings were 20 feet down through clay, no rocks below. However, there is a hardpan so geotech says that injection is not possible.

What I want to achieve is less swell to prevent deflection and sheetrock cracking.

One of the neighbors has engineered piers going down 20 feet for his foundation, and they are moving differentially up. My geotech puts the active zone at my location at 12 feet.

Lime conditioning is possible. It would also be possible to overexcavate and replace with crushed limestone. I have not found a source of nonexpansive clay for select fill (McKinney TX).

Your thoughts appreciated.

 

[civilperson]

Lime stabilization is an established and proven method of soil improvement. Drainage and grading measures to keep the subgrade from moisture will also be necessary.

 

[oldagpe]

Thanks, civilperson.

The next alternative is pier and beam. Obviously, 20 feet is not a sufficient depth.

Assuming that 12 feet is the depth of the active zone, and using a bored shaft filled with concrete in a 12 inch diameter, caged to resist uplift, any comments to Nelson and Miller Expansive Soils: Problems and Practice in Foundation and Pavement Engineering suggesting 20 times the shaft diameter depth required below the active zone.

Already realize that 32 feet will be greater than total length < 30 diameters.

Numbers in this region for Das 1984 uplift run 2000 psf and 30 degree angle.