Tunneling Under Sidewalks and Driveways
DEAR TIM: I am installing some low voltage lighting in the planting beds in front of my home. But a sidewalk is blocking me from running the cable from bed to bed. I do not want to have to break apart the concrete or saw cut a small groove through it. Is there an easy way to go under the sidewalk with disturbing its integrity? Surely you had to do this once or twice and can share your secret tools and tricks. Mike S, Kalamazoo, MI
DEAR MIKE: How right you are. I can't think of the number of times I had to extend a drain pipe, cable, irrigation line, gas line, etc. under a driveway, sidewalk or retaining wall without disturbing the finished surface material. Sometimes, the task was easy; other times it was a nightmare. But you are correct in thinking, I learned some creative solutions to the different challenges.
My first inspiration for creating invisible pathways came from a fantastic backhoe operator I used to hire. We had to extend a pipe under a six foot wide sidewalk and digging a tunnel by hand with a duckbill shovel gave me a headache just thinking about it much less from doing it.
The backhoe operator showed up at the jobsite with a large 16 foot long six-inch diameter steel pipe that had a coned-shaped metal end. He dug a two-foot deep trench perpendicular to the sidewalk and laid the pipe into the trench with the pointed end towards the sidewalk. He positioned the backhoe and used the hydraulic power of the machine to push the pipe under the sidewalk. The entire operation took about five minutes.
You don't need this type of machine or tool to solve your problem, but the point is, there are creative ways to tunnel under the surface. I learned another fantastic trick from a fellow plumber that will work for you. We had to extend a new four-inch diameter sewer line from an existing house to a new detached garage / pool house that was seven feet away. We drilled a six-inch diameter hole through the concrete foundation of the house so that a four-inch PVC pipe could be inserted and tilted at a slight upward angle for drainage purposes.
This plumber used a reciprocating saw to cut a chisel point on a scrap piece of four-inch PVC pipe. The tip of the pipe looked like a giant hypodermic needle. We inserted the pipe into the hole and tapped a block of wood fitted against the end of the pipe with a sledge hammer until it pierced into the clay soil about four inches. Using a large pipe wrench we rotated the pipe so that the chisel point end cut out a soil plug. We pulled the pipe back into the basement, removed the soil from the inside and repeated the operation. Within an hour, we had a perfect pathway created that passed from the existing basement under the footer of the new building.
Watch Tim demonstrate this method on his Underground Wire Tunnel Video.
You can do this exact same thing to create your pathway, but use a smaller one and one-half inch diameter PVC pipe. You will have to hand dig a trench as my backhoe operator did so that the pipe you are using is parallel with the top surface of the sidewalk. If your soil is rocky, you will probably have to use a steel pipe with the chisel cut instead of the more-fragile plastic piping.
Another ingenious method that is somewhat messy, yet effective, is cutting a pathway using a pressure washer. If your wand has a 0 degree tip, you will be in business. A 0 degree tip creates a powerful narrow stream of water not much wider than a pipe cleaner. You will have to dig a similar trench perpendicular to the sidewalk so you can get the wand parallel with the top surface of the sidewalk.
Wear goggles as the high-pressure stream of water will blast out mud, small stones, etc. back towards you as you point the wand directly into the dirt. This method is very effective and depending upon your soil type, you can create a pathway in a matter of minutes.
Stop the spray every few minutes to inspect the size of the pathway you are creating. A two-inch diameter pathway one foot under the sidewalk should not create any type of structural problem for the sidewalk. If you want to minimize or eliminate any settlement problems, fill the cavity with sand after the electric cable is installed. Pour sand into the hole and use water from a garden hose to help move it under the sidewalk.
You can dig pathways by hand with a special duck billed shovel. These tools have 16-inch long narrow blades that will create a six or seven inch diameter hole. But the limit of the digging is limited to about half the length of the shovel. It is also very hard to drive the shovel into soil when you are on your knees or twisted like a pretzel in a larger trench.
The chisel-point pipe method works very well if your soil is primarily clay or a sandy clay. The twisting motion of the pipe cuts a crisp soil plug each time. Use a smaller diameter pipe shoved into the pointed pipe to remove the soil plug.
If you use a pressure washer, you can actually use a pipe to help control the size of the pathway. As you start to cut the soil with the water insert a pipe that is as long as the sidewalk is wide. Slide the pressure washing wand into the pipe and start to tap the pipe under the sidewalk as the water cuts the channel. If the end of the pipe is always in contact with the soil as the water blasts away, you will only remove as much soil as the outer diameter of the pipe that is surrounding the wand. Leave the pipe in place once the pathway is created to eliminate settlement problems.