Gravel, Stone and Soil Delivery in Apex, NC

A slope of sandy loam over a tight subsoil

The USDA soil survey maps a Creedmoor-Green Level complex, 10 to 15 percent slopes, at the center point of ZIP 27502. Creedmoor is the main soil and makes up 60 percent of the unit. Its top mineral layer is sandy loam.^[1]

The sandy top hides a slower layer. Creedmoor is rated moderately well drained, and its hydrologic group is C/D. The survey uses a split group like that when the answer depends on the water table: the soil acts like group D, with very slow infiltration, while the water table is high, and like group C, with slow infiltration, where it has been drained.^[1]

Shrink-swell in the top meter is moderate, at 3.6 percent. Put together, these ratings describe ground where rain soaks into the sandy surface, meets a slower layer below and moves sideways down the slope. That water can surface again at the foot of a hill or under the low end of a drive.^[1]

Triassic rock of the Chatham Group

Under the center point, the state geologic map shows the Chatham Group, part of the Newark Supergroup, mapped as undivided. Its rocks are conglomerate, sandstone and mudstone, laid down in a basin during the Triassic.^[2]

Mudstone weathers into fine, dense material that slows water, which fits with the C/D rating above. Sandstone and conglomerate break into coarser, grittier fragments. A test hole on a lot near the center point may show a reddish, layered mix of both. The ground there sits 310 feet above sea level.^[1],[2],[3]

Triassic basin rock like this tends to weather into flat, platy fragments and slick clay. A trench wall in it can look firm on a dry day and slump after rain. When you dig for a drain or a footing, keep the spoil pile well back from the edge, and backfill around pipes with clean stone instead of the dug material.^[2]

Wet winters and freeze dates at New Hill

The NOAA normals station for Apex is New Hill, NC, about 2 miles away. It averages 47.1 inches of precipitation a year. Lows reach 32 F or colder on 89 days a year at that station.^[4]

The median last spring freeze at New Hill is April 6. The median first fall freeze is November 3.^[4]

Freezing nights and slow-draining subsoil make a poor pair under a gravel drive. Water trapped in the base or just under it can freeze and lift the surface, then leave a soft patch when it thaws. Keeping water out of the base, with a crown, side drains and fabric, is the best defense.^[1],[4]

Rain at New Hill arrives in every season, and a yearly total of 47.1 inches means the subsoil rarely dries out for long. Spring often brings the softest ground of the year, when thawing and rain overlap. Staying off a soft new drive until it firms up, and adding stone only after the base has drained, saves repair work later in the year.^[4]

Building a drive on a 10 to 15 percent grade

Slope is the first thing to plan for. A drive that climbs a grade of 10 to 15 percent sends rain straight down its length unless you stop it. Shape the subgrade with a cross slope toward the uphill ditch or the downhill edge, then lay a woven fabric over it so the subsoil cannot mix into the stone.^[1]

Use Road Base for the structural layer, spread and compacted in thin lifts. Under the steepest part, a first layer of 1-1/2" Crushed Gravel or #4 Crushed Stone gives extra strength where the ground stays damp. Finish with Driveway Gravel or #57 Crushed Stone, which lock together on a slope.^[1]

Add a cross drain every so often: a shallow, angled trench filled with Drain Rock, or a low hump in the base, that turns water off the surface. At each outlet, a pad of Riprap on fabric keeps the water from cutting into the sandy loam.^[1]

At the foot of the drive, look for a spot where seepage comes out of the slope after rain. A French drain across the drive at that point catches the water moving through the subsoil before it softens the base.^[1]

Choosing between #57 and #67 for drainage

Two stone sizes show up in drainage work around Apex, and either one can do the job. #57 Crushed Stone is the larger of the two, with more open space between pieces, so it moves a lot of water fast. It is the usual choice around a pipe in a French drain or under a gravel patio on wet ground.^[1]

#67 Stone is a little smaller and packs a bit tighter. It drains well and makes a smoother surface to walk on, so it suits a drainage strip beside a walk or a stone bed that people will cross. For the deepest, wettest trenches, #57 Crushed Stone or Drain Rock is the safer pick. Wrap either one in fabric where it meets sandy loam, or fine soil will work into the gaps over time.^[1]

A third option is Pea Gravel, which drains well but rolls. It fits a flat drainage bed under a downspout or a play area, where nobody needs a firm surface. On the slopes mapped at the center point, keep it out of trenches that run downhill, since water can carry the round stones along the trench floor.^[1]

Homes, beds and the North Carolina spec

The Census counts 18,190 housing units in ZIP 27502. Of these, 72 percent are detached single-family houses, the median build year is 2005, and owners live in 82 percent of the occupied homes. Apex as a whole has 26,500 housing units, 67 percent detached, with a median build year of 2008.^[5]

Yards around newer homes are often graded with subsoil left near the surface. For beds, bring in Garden Soil or Topsoil mixed with Compost and raise the planting area a little above the grade. Cover with Brown Shredded Mulch or Black Shredded Mulch to hold the soil on slopes and keep weeds down.^[1]

Lawns on graded subsoil often thin out in wet spots and bare patches. Spreading a layer of Topsoil before seeding, and raking it level, gives grass a better start. Where a lawn keeps failing in a damp low corner, a rain garden or a bed of River Rock may be a better use of the space than more grass seed.^[1]

The North Carolina Department of Transportation names its stone layer under pavement Aggregate Base Course, Section 520, in the Standard Specifications for Roads and Structures (January 2024).^[6]