Build a Culvert that Looks Like a Stone Bridge

Create a dry-stacked stone driveway culvert that looks and functions like a beautiful stone bridge.

| April/May 2018

Taking on the task of building a dry-stacked stone culvert — that is, a stone culvert that doesn’t use mortar — presents the very satisfying opportunity to build something that’ll be strong enough for you to drive a vehicle over and will look very much like a beautiful dry-stacked stone bridge. There’s no reason to go with bags of sand or cement, blocks, plastic, metal, or anything man-made in your finished culvert. With a little bit of effort and the right stone material, a culvert can become the showcase of your property. After all, it’s the first thing people will see when they pull up to your drive. Why not make it stunning?

Creating Your Stone Culvert

Start by digging out and removing the dirt from the location of your future culvert, leaving a 3- to 4-foot wide ditch on either side of where the culvert is to go. The ditch should be deep enough to allow the top of a 1- to 2-foot channel to be about 2 feet below grade. You’ll have to dig at least 11⁄2 feet farther out than the area that crosses under the driveway so the water will run correctly in the direction you require. You’ll then dig a trench 3 inches deep and a foot wider than the width of your culvert opening. Fill the trench level with 3⁄4-inch clear, crushed, sharp aggregate, and then lay flagstone material — or even patio slabs — that are approximately 2 inches thick on top of the aggregate to form a level bed for the watercourse. When you lay the flagstones, you’ll want to butt them close to one another and extend them at least 6 inches past the length of the footprint of your culvert on either side.

To create a small waterfall, you can make your culvert’s openings slightly higher than the ditch it will be flowing into. In this case, you might like to build small stone embankments around the area the water will flow into. Conversely, you can create a small, rounded retaining area in which the water can pool before it goes through the culvert; do this by situating your culvert so it’s slightly higher than the water in the ditch flowing up to it.

Next, lay your form onto the flagstone watercourse. A length of metal or plastic culvert tubing will work well for this purpose. The tubular form should be long enough to extend at least 11⁄2 feet past each opening of the finished culvert. This is so the tube can be supported at the ends. Raise the tube about an inch above the flagstone base by supporting it with a 2-by-4 resting on top of a 2-by-8 running through the tube (see illustration of stone channel in the photo slideshow). These boards should be longer than the tube so you can support the ends of the boards with concrete blocks that are resting on patio slabs placed temporarily at either end of the form. Place two wooden shims between the 2-by-8 board and the concrete blocks. The shims should be placed one on top of the other to form a rectangle that can be adjusted to be taller or shorter. This will allow you to drop the tube down and slide it out, making its removal much easier later in the process.

The stones you’ll need to collect to go over and around the length of the tubular form to create the stone channel don’t necessarily have to be rectangular; they’ll just need to have some length to them and not be too round. You’ll lay similarly sized stones in rows of approximately the same height, called “courses.” Starting from the visible sides, you’ll want to butt the stones tightly up to one another, making sure they all fit together snugly where they touch the tube. Add thin wedges of stone as needed so that each arch stone (called a voussoir) fits snugly into the structure. Place these wedges near the tops of the stones and avoid letting any of them slip down where they might create a pivot point between the voussoirs. For the best visual appearance, you’ll likely need to do some extra shaping to the arch stones that are visible on the outside of either end of the culvert so they fit together especially well.

Then, lay smaller stones on top of the stone tunnel. After you’ve laid these smaller stones, pack a minimum of 6 inches of gravel over the stone tunnel, and place landscape fabric on top of that. The final layer of road-grade aggregate on top of the fabric will bring the culvert up to driveway height. At this point, you can remove the tubular form.

3/28/2018 7:43:08 AM

Th is is beautiful and I really need this.. Im trying to figure out the costs of everything.

3/28/2018 7:43:02 AM

Th is is beautiful and I really need this.. Im trying to figure out the costs of everything.

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