Expansive Soil and Driveway Heave in Colorado Springs

A driveway on swelling clay can crack in patterns that no sealer will fix. When clay minerals take on water they expand, and when they dry they shrink, and the Colorado Geological Survey calls cracked and heaved driveways, sidewalks and patios very common indicators of the problem. Much of the plains side of El Paso County sits on clay loams weathered from shale, and parts of the west side sit on steeply tilted shale beds. Both behave very differently from the sandy granite soils of the foothills.

This guide covers where those soils are, what heave looks like on asphalt, how water from sprinklers, downspouts and summer storms drives it, and when the fix is drainage, patching or a new base rather than another coat. It draws on NRCS soil series descriptions, the El Paso County soil survey, Colorado Geological Survey hazard publications, NOAA climate normals and city and state code.

How swelling clay moves a driveway

Expansive clay is built from flat mineral plates, and water slips between them and pushes them apart; drying pulls them back together. The Colorado Geological Survey says such soils can expand up to 20 percent by volume when wet and exert a force of up to 30,000 pounds per square foot, and that engineers generally treat a volume increase of 3 percent or more as potentially damaging. It also cites an interstate in eastern Colorado where as much as a foot of uplift forced two concrete lanes to be repaired six months after paving was finished.

Asphalt does not resist that force; it follows it. A driveway is a thin, flexible mat on a compacted base, so when the clay under one part of it swells more than the clay under another, the mat bends and cracks along the line of greatest strain. The movement is reversible, too, which is why a heave crack can close during a dry September and open again after a wet spring. Unlike ordinary wear cracks, these do not stay where they started, and a coat of sealer over them lasts only until the next move.

Where the swelling soils are around Colorado Springs

The El Paso County soil survey maps a long list of clayey units, among them Razor, Midway, Kutch, Manzanola, Nunn and Heldt clay loams and Limon clay. NRCS describes Razor as moderately deep over calcareous shale, with 35 to 60 percent clay, slow permeability and softer rock 20 to 40 inches down. Midway is shallower, reaching shale at 10 to 20 inches with 35 to 45 percent clay and slow or very slow permeability. Kutch holds 35 to 60 percent clay over gray and olive clay shale that carries crystalline gypsum at about 30 inches.

The west side adds a second hazard. In 1999 the Colorado Geological Survey mapped expansive, steeply dipping bedrock in the western part of Colorado Springs, including the Pierre Shale and Niobrara Formation, and warned that shallow expansive layers can produce destructive differential heave. Its broader work on the Front Range piedmont describes heaving bedrock in the Pierre Shale and other Upper Cretaceous formations damaging houses, roads and utilities since suburban development began in the early 1970s. The city adopted a geologic hazard ordinance in May 1996 requiring such hazards to be identified and mitigated when land is developed.

Not every neighborhood has the problem. The Pring series, mapped in the foothill and Black Forest areas, is a coarse sandy loam weathered from arkose, with only 5 to 18 percent clay and rapid permeability, and the mountain towns up Ute Pass sit on crumbled Pikes Peak granite. On those soils, cracking is more often about compaction and edge support than swelling. The Monument page covers the snowy north end of the county.

Reading heave cracks on asphalt

Heave leaves a different signature from ordinary aging. Oxidized binder produces fine, random crazing and a gray, sandy surface spread fairly evenly over the sunny parts of a drive. Thermal cracking from cold nights tends to run straight across the drive at fairly regular spacing. Heave shows up as shape: a hump visible under a straightedge, a long crack along its crest, cracks fanning out from one wet spot, or a step where one side of a crack sits higher than the other.

Location is the other clue. Cracks that run beside a sprinkler line at the lawn edge, that circle a downspout outlet, or that follow the path where roof water crosses the drive point to water feeding the clay from the side. Heaving bedrock can look different again: a 1995 Colorado Geological Survey report on the same hazard in Douglas County described elongate mounds and ridges up to 2 feet high, tens of feet wide and hundreds of feet long, which cross a lot without regard to where the driveway sits.

• Surface aging: gray, rough, sandy surface and fine random cracks, with no change in level
• Thermal cracking: straight cracks across the drive at intervals, widest in winter
• Heave: humps, crest cracks, stepped edges and cracks radiating from a wet spot
• Base failure: a web of small blocks and soft spots that flex under a tire

Water is the part an owner controls

Swelling needs water, and on a residential lot much of it is delivered on purpose. The Colorado Geological Survey's guidance for homes on expansive soil warns against planting next to foundations where irrigation water enters the soil, and the same logic protects a driveway edge. Colorado Springs already limits the habit: City Code 12.4.1304 prohibits irrigation that pools on or flows across a driveway into a gutter or storm drain, bans most watering between 10 a.m. and 6 p.m. from May 1 to October 15, and caps watering at three days a week.

The sky adds the rest in summer. At the airport, 8.68 of a normal 16.54 inches of precipitation falls in June, July and August, and July alone averages 1.8 days with half an inch or more. Downspouts that empty onto the drive and lawns graded toward the pavement concentrate that water at the edge of the asphalt. Extending downspouts, regrading soil so it falls away from the drive and adjusting sprinkler heads cost little and remove the cause rather than the symptom.

Sealing and crack filling belong to the same strategy. Hot-pour crack filling closes the openings that let storm water reach the subgrade, and a sealed surface sheds rain rather than absorbing it. Neither stops water arriving from the side, which is why drainage comes first on a drive that is already moving.

Repair choices and paperwork

When sections have heaved or broken, the choice is between patching the damaged areas and rebuilding the drive. A full-depth patch removes failed asphalt and wet base, lets the crew see and dry out the subgrade, and replaces it with compacted aggregate and new hot mix; asphalt patching explains how that is priced. If heave runs across most of the drive, replacement with the swelling clay dug out and a thicker, well-drained base is the durable answer, and new asphalt paving covers base design.

Records can help. Colorado law, C.R.S. 6-6.5-101, requires builders of new homes to give buyers a summary of the soil analysis and site recommendations at least 14 days before closing, plus a publication on expansive soils where they are present. The Pikes Peak Regional Building Department requires a soils report and engineered foundation design at the first inspection of a new house. Private driveways on grade are exempt from building permits, so the building department never reviews the driveway, but the house's soils report describes the same ground the driveway sits on.