Drain Rock in Virginia: Fill for Ground That Holds Water

Almost every order of drain rock placed in this state is a response to one of three grounds. Piedmont clay takes rain in slowly and then keeps it, so water stands against foundations and wall faces long after the storm has gone. The flat Coastal Plain through Hampton Roads, the Eastern Shore and the river necks has water close to the surface before it rains at all, and nowhere for more to run. West of the Blue Ridge, limestone valleys send water down into the rock rather than across the surface, which changes where a discharge should and should not go. The stone is the same in all three; the dig is not.

Digging in the shoulder seasons, not in a soaked spring

Timing is half the job, because the trench has to stay open and stable long enough to be built properly.

• Late autumn through early spring on the Piedmont gives workable ground, but a trench cut into clay after a long wet spell slumps and smears, and a smeared clay wall drains worse than the clay did before you touched it. Wait for a drier stretch rather than a warm one.
• Midwinter in the Shenandoah, Roanoke and New River valleys and in the mountain counties brings frozen ground and snow, which stops the dig outright at the times it is most tempting to get ahead of spring.
• On the coast, late summer into autumn is tropical storm season. That is when the drainage problem announces itself and the worst time to have a trench open. Plan the work for the quieter part of the year and use the storm season to see where the water actually goes.
• Any time of year, the trench wants finishing the same week it is opened. An open trench left through rain fills with silt and soft spoil.

Getting the line and the fall set before anything arrives

• Walk the site in heavy rain first, or at least after it, and mark where water genuinely runs. A drain built on a guess moves water nowhere.
• Settle the discharge point before the dig. Water has to leave somewhere lower, and in karst country west of the Blue Ridge, concentrating a discharge into one spot is worth a hard look before you commit.
• Cut the trench to a consistent fall along its run. Fall matters more than depth.
• Line it with a separation geotextile, lapped well up both walls, so clay and fine sand cannot work into the voids.
• Bed the perforated pipe on a layer of stone rather than on the trench floor, holes down, then fill over it.
• Close the fabric over the top of the stone before any soil goes back.

Where drain rock goes: foundations, wall faces, leach fields and ditch lines

The material is washed, with the fines and dust taken out, running from 3/4 inch up to 1-1/2 inch, and it is listed in rounded and angular form. That choice matters more than people expect. Where backfill above will bear on the stone, the angular form interlocks and keeps the voids open under that load. Where the stone stays visible in a landscape run, the rounded form looks like it belongs there.

A foundation drain is the most common order. It carries groundwater away from basement walls and footings, and it is worth building to the full height the design intends rather than to the depth the shovel gets tired at.

Retaining wall backfill gives water a route down and out behind the face so pressure does not build against the wall. Build it up in lifts with the rest of the backfill rather than dropping it all in at the end, and keep the drainage zone separated from the soil behind it.

Septic and leach fields use it as the drainage layer. That work is designed and inspected by someone else, so build it to the specification you have been given and nothing else.

A yard ditch or swale line that carries low flows can be lined with it over fabric. A culvert outlet taking real storm flow is a different job: the water arrives with enough energy to move a stone this size, and that outlet wants RipRap sized for the flow instead.

The low corner that needs fill rather than stone

A low spot or a yard regrade comes up constantly alongside drainage work, and drain rock is the wrong material for it. A low area is a volume problem, not a flow problem: you are raising a grade so water runs somewhere else. Filling that volume with washed stone is expensive in tonnage terms and leaves you with a stone-filled hollow rather than a shaped surface.

Raise it with Fill Dirt, compacted in lifts, shape the contour so runoff leaves the way you want, then put Top Soil over the top where grass has to grow. Use the drain rock only for the trench that takes the water off the newly shaped ground.

Counting a 46 foot foundation drain, a ditch line and an outlet

Length times width times depth, all in feet, gives cubic feet. Divide by 27 for cubic yards. The site's calculator pages do not list this product by name, so the figures below use the closest listed family, 3/4 inch crushed stone at about 2,800 lb per cubic yard, roughly 1.40 tons. Treat the tonnage as approximate.

• Example, a foundation drain 46 ft long, 18 inches wide, filled 24 inches deep: 46 x 1.5 x 2 = 138 cu ft. 138 / 27 = 5.1 cubic yards, about 7.2 tons.
• Example, a low-flow ditch line 32 ft long and 2.5 ft wide, lined 4 inches deep: 80 sq ft x 0.333 = 26.7 cu ft. 26.7 / 27 = 1 cubic yard, about 1.4 tons.
• Example, the culvert outlet that needs armor instead, an apron 10 ft by 6 ft at 8 inches: 60 sq ft x 0.667 = 40 cu ft. 40 / 27 = 1.5 cubic yards. Armor stone runs about 3,100 lb per cubic yard on this site's figures, roughly 1.55 tons, so about 2.3 tons of RipRap.

Subtract nothing for the pipe unless it is large; on a domestic run it is inside the rounding. The river rock calculator sizes this material.

The first year, and what to check after a big storm

• Expect some settlement over the trench line in the first few months as the stone finds its arrangement. Top the soil back up rather than letting a channel form along the run.
• After the first heavy rain, go and look at the outlet while it is still running. Water leaving cleanly is the only proof the drain works.
• Watch for silt or fine sand appearing at the outlet. That means the separation has been breached somewhere and the voids are filling.
• Keep the outlet clear of leaf litter and mulch through autumn. Most drains that stop working stopped at the last three feet.
• Where the run crosses a drive or a path, check for a dip forming and fill it before it becomes a pothole.

Pick a quantity and a delivery date on this page once the trench is open, the fabric is on site and the spoil is out of the way. Delivery is arranged at checkout from your ZIP code, and the truck needs a route in and a firm spot it can tip on.