Grading and Base Repair in Madison, WI

Base repair means digging out the stone and soil that have lost strength under asphalt and rebuilding them so the next surface has firm support, and around Madison it often decides whether a paving job lasts. Frost is the reason. The City requires deck footings at least 48 inches deep to get below frost heave, but pavement is never built that deep; it relies on a compacted, drained stone base to ride out the roughly 87 days a year when the airport's thermometer crosses 32 degrees in both directions. Where that base has filled with silt, or sits on wet or organic soil, no new surface will hold for long. The driveway paving page covers the asphalt that goes on top.

The soils explain most base failures here. USDA descriptions of two series whose official type locations are in Dane County, Dodge and Kegonsa, start with silty loess at the surface, over glacial till in Dodge's case and sandy outwash in Kegonsa's. Wisconsin's local-roads program names fine-grained silts and clays as the frost-susceptible soils, and WAPA's design guide rates subgrades with half or more silt and clay as poor support. In low, wet ground, very poorly drained lake-bed soils such as Wacousta are frequently ponded, and WAPA's guide says organic soils and soils with a CBR below 2 should be avoided, removed and replaced, or stabilized.

Rebuilding a base is about stone, depth and compaction. The City's driveway base specification is Gradation No. 2 crushed aggregate, 1-1/2 inches and smaller, six inches deep unless otherwise specified, and WAPA pairs poor subgrades with 9 to 12 inches under a home driveway. Stone goes down in compacted lifts rather than one thick dump, and the finished base should be proof-rolled with a loaded truck. Any area that ruts or pumps gets dug deeper and rebuilt before paving starts.

Grading sends water where it cannot hurt the pavement. WAPA's guide calls for at least a 2 percent cross slope on crowned surfaces and 2 to 5 percent on parking areas, and its owner guide stresses draining water away from the house. Downspouts that empty onto a driveway, lawns graded toward the pavement and settled spots that hold meltwater all feed water into the base, which is where the spring thaw does its damage between early March and early May.

Larger grading jobs need permits in Madison. An Erosion Control Permit is required for disturbing more than 4,000 square feet, filling or excavating more than 400 cubic yards, or building an access drive longer than 125 feet, and stormwater management rules apply past 10,000 square feet of disturbance. In Cottage Grove, land disturbance falls under Chapter 163 of the village code, and anywhere in Wisconsin digging starts with a Diggers Hotline locate request. The parking lot page covers the larger sites.

Costs track depth and access. HomeGuide puts grading for drainage at $1 to $3 per square foot and crushed stone at $30 to $60 a ton, while Angi and HomeAdvisor put full excavation and grading ahead of new pavement at $5 to $10 per square foot. Undercutting a soft area deeper than planned, or hauling away organic soil, moves a job toward the top of those ranges.