D-1, pit run, 3-inch minus: which one, and in what order

The short version

Pit run is the cheap stuff that goes deep. 3-inch minus is the middle layer that builds up soft ground. D-1 is the expensive, engineered top that locks together and carries the wheels. Bottom to top: pit run, then 3-inch minus if the ground needs it, then D-1. That is the whole article; the rest is why.

Pit run: as the bank gave it

Pit run, which the state calls Type II and old-timers call bank run, is gravel dug from the pit face and loaded without screening. Sand, rock up to about four inches, and whatever fines were in the bank. It is the cheapest material on any Anchorage price list, about $9 a yard this season, and it is cheap because nobody did anything to it. That is also its virtue: it drains, it fills, and under a foot of better material nobody will ever see it. Use it to get above wet ground and to make up depth.

3-inch minus: screened, not crushed

Run pit material over a 3-inch screen and you get 3-inch minus: everything three inches and down, fines included, big rocks removed. At about $11 a yard it costs a little more than pit run and it behaves better, because without the four- and six-inch rocks it grades flatter and packs more evenly. It is the right sub-base on a soft lot and a fair top course on a rural driveway where you will accept some loose stone. It is not a finish course for a driveway you care about; the rounded river rock in it never fully locks.

D-1: crushed and graded to a spec

D-1 is crushed rock, not screened bank gravel, graded to the Alaska DOT&PF base course specification: a controlled blend from about an inch down to dust, with angular faces that bite into each other under a roller. It is what the state puts under asphalt. It costs $22 to $30 a yard depending on the pit, sells by the ton at about 1.4 tons to the loose yard, and it is the only one of the three that turns into a hard, smooth, water-shedding surface when you compact it damp. Our D-1 delivery page covers placement.

Why the order matters in Anchorage specifically

Frost. The Municipality requires footings at 42 inches because the ground here freezes deep, and a driveway on wet silt heaves every spring no matter what is on top. The base layers exist to get the surface above the water and let it drain, so the frost has nothing to lift. Pit run does that cheaply. D-1 then gives the wheels something hard. Skip the base and the D-1 sinks; skip the D-1 and the base ruts.

When each one is the right single material

• Just pit run: a temporary construction access, a pad you will pour over next week, filling a hole.
• Just 3-inch minus: a rural driveway on well-drained gravelly ground where you will top it up every few years and do not mind loose stone.
• Just D-1: a walkway, a patio base, a top-up on a driveway that already has a good base.

What to order for a typical driveway

For a 60 by 12 foot driveway on average Anchorage ground: 8 inches of pit run, about 20 loose yards, then 4 inches of D-1, about 10 loose yards. In our 12-ton trucks that is five loads: three of pit run and two of D-1, the second one light. Compact each lift. The load calculator does the arithmetic for your dimensions, and the driveway cost page prices the whole thing.