Hand-Dug 8-Metre Tunnel Under a Cobblestone Driveway

I needed to run an electrical conduit from my house to the garden, on the other side of a cobblestone driveway. Opening the driveway meant lifting the cobbles, digging a trench and laying everything again, and the only other route was a 25 m detour.

So I dug a tunnel under the driveway instead, by hand, starting from the crawl space under my house. The tunnel is about 8 m long and 60 cm deep, and holds a Ø90 mm PVC pipe, big enough for a 40 mm electrical conduit.

It took me about 15 hours of work. A company had quoted €3000 for the job, and the driveway was never touched.

The drawings in the steps explain how it works.

1. Steel tube Ø110 mm, 2.5 m long, with one end cut at an angle (bevelled)
2. ground auger Ø100 mm (item 141024): 1 m long with a 0.6 m T-handle and a double spiral. It fits inside the steel tube. About €40.
3. ground auger Ø80 mm with 9 m extension tube (item 270540): the auger, a 0.6 m T-handle and 8 extension tubes of 1 m (square 30 × 30 mm) that screw together with the screws supplied. About €135. I used all 8 extensions, plus a square tube to finish.
4. PVC pipes Ø90 mm (3 + 3 + 2 + 1 m) and PVC glue
5. Pressure washer with a drain-cleaning nozzle
6. A home-made spiked tool for hard clay
7. Old car rims to support the auger in the crawl space
8. Tools to open the walls (hammer drill, chisel, angle grinder)
9. Buckets to take out the soil
10. A spade for the exit pit

My house has a crawl space under the floor. On one side of the house, a cobblestone driveway separates it from the garden. The cobbles are laid on sand over a stabilized base, so opening the driveway properly is a big job.

The idea: start from inside the crawl space, go through the foundation wall, and dig a horizontal tunnel about 60 cm under the driveway until I come out in the garden, behind the fence.

The drawing shows a cross-section of the site. On the photos, the red lines show the tunnel location, and I marked the line on the cobbles with tape.

Before you start: check what is already buried under the driveway (water, gas, electricity, drains). If you are not sure, ask the utility companies for their plans.

In the crawl space, I made a hole through the foundation wall, at the level of the tunnel and facing the garden.

Keep the hole just big enough to work through: the wall carries the house.

Just outside the wall, there is a gravel drain along the foundations. Gravel collapses as soon as you dig into it, so an auger alone doesn't work there.

I used a steel tube Ø110 mm, 2.5 m long, with one end cut at an angle. When you push and turn it, the bevelled end cuts into the ground like a spoon. Inside the tube, the Ø100 mm ground auger takes out the gravel: its spiral fits inside the tube.

Push the tube a little, empty it with the auger, and repeat until you are through the drain. The soil goes out in buckets through the crawl space.

After the drain, the ground is sandy clay. From there, I switched to a PVC pipe Ø90 mm and the Ø80 mm ground auger with its extension tubes. The auger goes through the pipe and drills just ahead of it, then I push the pipe forward.

Each time the tunnel gets longer, screw a 1 m extension tube onto the auger. Pull the auger out regularly to empty the clay: this is the slow part of the job.

The drawing shows how the tubes and augers fit together.

In some places, the clay was too hard for the auger. I made a simple spiked tool to break it up first, then the auger can take it out.

The more pipe there is in the ground, the harder it is to push. Regularly, I flushed the tunnel with a pressure washer and a drain-cleaning nozzle. The water softens the clay, carries it back out and helps the pipe slide again.

Expect mud in the crawl space, and keep buckets ready.

This is the trick that saved me a lot of time.

With all the extensions, the auger is 9 m long (the auger, 8 extensions of 1 m and a square tube to finish). To pull it out of the tunnel and empty it, you need 9 m of free space behind the wall, in line with the tunnel.

My crawl space has an inner wall. I made a hole in it, in line with the tunnel, so I could slide the whole auger back along the length of the house. I laid the auger on old car rims so it slides easily and stays straight.

Without this hole, it would still have been possible, but much slower: each time I pulled the auger out to empty it, I would have had to unscrew the extensions one by one, then screw them all back together before going in again.

I glued the PVC pipes as they went in: after the first pipe, 3 m, 2 m and 1 m, so 9 m in total, with about 8 m in the tunnel.

When I was close to the end, I dug an exit pit in the garden, behind the fence, to meet the pipe.

After about 15 hours of work, a Ø90 mm PVC pipe runs 8 m under the driveway, and the driveway looks exactly as before. A company had quoted €3000 for the job.

The electrical conduit can now go through the pipe from the crawl space to the garden.

A few lessons:

1. You need some luck: a big stone or a root can stop you.
2. In clay, water is your friend.
3. Every metre you drill is a metre of trench you don't have to dig.