Concrete Driveways in Centennial, CO

Centennial is a south metro city in Arapahoe County, incorporated relatively recently out of previously unincorporated area, which occasionally confuses permitting: the city is the relevant authority now, not the county, and older guidance found online may say otherwise.

It sits in the part of the metro where expansive soil conditions are most consistently discussed, and the research in this region is worth taking seriously before a substantial pour. USGS work on nearby Pierre Shale found bentonite beds swelling 39 to 43 percent in testing against 2 to 8 percent for ordinary silty claystone, with differential swell between adjacent beds the primary factor in severe damage. Later work found the worst heave coinciding with steeply dipping claystone carrying thin highly plastic bentonite layers, and damage falling away as depth to bedrock increased.

What follows from that is specific rather than general advice. For a significant slab, a geotechnical opinion on the actual lot is the cheapest insurance available, and the Colorado Association of Geotechnical Engineers publishes the guidance local engineers use for slab performance risk in these soils. For ordinary flatwork, the controllable factors are drainage, base preparation and mix specification.

The moisture point deserves repeating because it is the one homeowners can act on without a contractor. Wetting and drying is what drives movement in these soils. Downspouts discharging against the house, irrigation running close to the foundation, and grading that has flattened over the years all feed the problem, and all are cheaper to fix than a slab.