What is Under-Slab Tunneling? (Definition, Process, and Cost)

You have just been informed that there is a leak in or under your slab foundation that requires plumbing repair. Maybe your mind goes to visions of jackhammers dancing in your head (not as nice as sugarplums no matter what time of year it is). Or maybe you are not sure what to expect at all, except that it sounds messy.

Just imagine all the mess that would result from someone breaking a hole in the floor of your home with a jackhammer. That room becomes a disaster zone and then you have to clean up a big mess. It’s in the kitchen too, and you probably won’t be able to use that room for a while so . . . What if I told you it didn’t have to be that way?

There’s this *new thing* (it’s not really new, but a lot of people don’t know about it) called under-slab tunneling that keeps all the mess away and allows you to continue using your home as usual. This method allows for any repairs that need to be done underneath and outside the home to be completed with no holes or debris inside the house. Seems like a huge plus, right?

At Anchor Foundation Repair, under-slab tunneling is one of our primary services and we regularly tunnel under homes. Because we do this quite a bit, our team of professional experts knows the proper techniques to remove and then replace the dirt under your home with future stability in mind at all times.

About 35 to 40% of our home foundation repairs include the need for tunneling. Other times, homes just need tunneling only, just to help the plumber gain access to the repair point. Either way, we have a great deal of experience creating and filling proper tunnels—making under-slab tunneling one of our specialties.

Anchor Logo

Although Anchor Foundation Repair does not fix the plumbing problem under your slab, we clear the way to make it easy for your plumber to reach. We also keep the proper care of your home as our highest priority. 

In this article, we will explain the special characteristics, the process, and estimated costs of tunneling under your home. We do this to help you decide if under-slab tunneling is a workable option to handle your needed plumbing repair.

What is under-slab tunneling?

It sounds complicated, but it’s pretty straightforward. A crew would dig underneath the concrete slab foundation of your home to reach a certain point where plumbing repairs need to be made. They use specialized shovels and tons of hard dirty work to dig a precise 3-foot by 3-foot square tunnel under your home.

Your plumber and your foundation repair specialist will develop a plan together that reaches the needed location using the shortest length of tunnel possible. Keeping the tunnel as short as possible ensures the lowest cost as well as the fastest, most efficient route. 

The quickest way from one place to another is the shortest, straightest line without obstructions. Things like patios, sidewalks, decks, or other hardscaping are examples of obstructions that can cause a different starting point in some cases. 

Or maybe there is a tree or air conditioning unit that would be in the way or somehow be compromised by the digging, the starting location might be moved farther out. But the goal is always the shortest and fastest tunnel length.

How long does it take to dig a tunnel?

On average, a tunneling crew can dig about 5 to 8 feet per day. An average tunneling job could be around 10 to 15 feet long, taking two to three days to complete. This all depends on where the under-slab plumbing leak is located and how large the home is in the first place. The Anchor crew has dug tunnels as long as 70 to 90 feet, but that is unusual.

The excavated tunnel allows the plumber to access and repair the plumbing lines underneath the home from the outside rather than inside. The most common issue needing repair are drain lines leaking underneath the foundation.

underground drain lines
Mighty fine lookin’ tunnel.

Why use under-slab tunneling?

The #1 benefit of using under-slab tunneling is that there is no mess inside the home when repairing a plumbing issue. Having under-slab plumbing fixed without tunneling can be intrusive to your daily life in many ways.

A disaster zone best describes what a home looks like while having portions of the foundation torn up for under-slab plumbing repair. A crew would jackhammer through the concrete, producing excessive noise, dust, and debris. So much for naps and Zoom meetings . . .

Dirt will be piled somewhere nearby the access point and you would likely need to avoid the area completely during the entire process. Since we know that this repair is to address plumbing issues, the area you have to avoid in your home is probably a kitchen, bathroom, or laundry room. You didn’t really need to shower, did you?

Not to mention all the people that will be coming in and out of your home to do all this work. Sounds fun, right?

On top of having the mess in your home, how long the repair takes will be how long you have to live with that massive hole in the floor. You might even consider moving out temporarily to avoid living in the situation. That is an added cost or inconvenience as well.

Using under-slab tunneling prevents all these problems. We’re a big fan of tunneling in case you couldn’t tell.

Under-slab tunneling moves the mess and disaster zone outside. Under-slab tunneling allows the plumber to move freely underneath the foundation of a home to make the needed repairs. Meanwhile, you can be inside the house living normally: cooking, bathing, Zooming, and/or napping . . . don’t forget the napping . . . 

Have a plumber determine the exact location of all plumbing failures.

It’s important to know where the plumbing is failing for sure. All tunneling jobs depend upon reaching a particular location or locations under the home. The cost and time it takes to tunnel all depend on the length of the tunnel needed. So definitely get that information before moving to the next step.

How does under-slab tunneling work?

When a professional foundation repair crew performs the work, under-slab tunneling is a safe and effective way to fix any of a home’s underground plumbing issues. Once the plumber knows and locates the point of failure, the work can begin from the planned starting point. 

Step 1: Digging the Tunnel

The crew will first dig straight down to get underneath the exterior wall of the home. The exterior wall has a support beam under it that carries the load of that side of the home and penetrates into the ground. Depending on the home’s age, the vertical hole could be from 3 to 6 feet deep to get all the way underneath that beam and to the other side of that first underground hurdle.

Once they get completely under and past the exterior wall’s support beam, the tunnel will return to vertical and go up until the bottom of the concrete floor or slab is reached. This is the underside of your foundation, which will then become the “ceiling” of the tunnel. This creates the safest tunneling environment by eliminating the possibility of dirt falling on a person or creating a cave-in.

The crew will then turn horizontal again and continue digging out a 3-foot by 3-foot tunnel to the plumbing failure point. This allows plenty of room for the plumber and any tools needed to be brought down for the plumbing job. The tunneling team’s job is then on hold until the completion of the plumbing repair.

Tunnel under pier and beam home
Do you really want to dig this tunnel?

Please note: Asking an untrained person to dig a tunnel under your home is never a good idea. It’s way more than just hard work that “anyone with a shovel” can do. While you could hire a day laborer, they would not have the experience or skill to dig or backfill properly. 

Digging a tunnel like this is very hard work and requires skill to get it done quickly and well. If someone with no experience tries to tackle it, they begin to see that it is too much for them to handle.

We had one actual customer try to dig his own tunnel and he gave up after a few days when he realized how difficult it was. Many times we have also had to bail out a plumber that thought they could do it themselves and we were asked to take over the tunneling portion of the job for them.

Step 2: Repairing the Plumbing Problem

A plumber of your choice will then come to complete the repairs, as long as they are comfortable with working in a tunnel as some may not. If you do not have a special plumber in mind, we can also recommend one for you that has experience with under-slab tunnel work. 

A reputable foundation repair crew would ideally coordinate with the plumbing contractor to ensure that timelines meet up and should help to keep your repair moving quickly.

Pressure testing of the repaired plumbing lines is done to make sure that everything is sealed up well and no further leaks are detected. Sealed plumbing lines are very important to the next step of the process and the continued health of your foundation.

Step 3: Filling in the Tunnel

Once repairs and pressure testing have proven successful, the tunneling crew will return to fill in the tunnel correctly, using both the removed dirt as well as new dirt as needed. This is where the expertise of having a foundation repair company do the tunneling comes into play.

Mud-pumping machine image
Mud-pumping machine at work

A foundation repair company tunneling underneath your home will have the right mindset for the future stability of your home’s foundation. With this at the forefront, the team will begin to fill in the tunnel with the excavated fill that was previously removed.

Once the tunnel is filled and the start hole sealed off, the final step is called mud-pumping, which provides the most thorough support under your home. Mud-pumping sends a combination of Portland Cement, sifted topsoil, and water with pressure under the slab. 

This finishing process allows for even the smallest pocket of space to be filled correctly and provides proper support to your concrete slab foundation. This final mud-pumping step is one of the most important to minimize any opportunity for future settlement, erosion, or movement of the foundation as a result of the tunneling process.

How much does under-slab tunneling cost?

Like many repairs needed around the home, the cost will vary depending on each situation. Most commonly, under-slab tunneling is priced by the foot which is why the exact location is important. The price per foot is a great place to start when estimating the cost of tunneling. 

Expect the price of tunneling to fall somewhere in the $200-$500 per foot range. This price point will vary from company to company and location to location. These individual circumstances make pricing for tunneling fluctuate and also depends on the cost of materials in a particular area.

Tunneling diagram

A typical example might be a traditional hall bathroom, needing about 8 to 10 feet of tunneling. A diagram is shown here that illustrates where the plumbing drain lines are located (by the blue lines) and where the tunnel would be created (by the red rectangle) to access all three of the drain lines in this example bathroom.

The cost of the tunneling, backfilling, and mud-pumping services in this example would be somewhere between $3,000-$4,000. This price is based on the local area of Bryan/College Station and typical tunneling needs for this hall bath example. 

The cost of a complete project will also vary based on the amount of repair needed to be done to the home’s plumbing. The cost for the plumbing repairs would be determined by the plumber and be in addition to the tunneling cost.

Is under-slab tunneling right for your home?

Under-slab tunneling is more desirable to some homeowners. As stated earlier, one significant advantage is that there is no mess and no tearing up the floor of the home. If you have recently renovated your flooring, you probably don’t want to undo all that nice work. 

Newly renovated homes will benefit the most from under-slab tunneling, as well as a homeowner who wishes to remain in the home during all the repairs. 

By contrast, a homeowner that is already in the middle of an active renovation (i.e. you might be living elsewhere at the moment) could use the “jackhammering and breaking through the slab from above” method. This method can cost less, and you won’t mind the mess, because you’re not there trying to use the home. Or maybe your biggest determining factor is lowest cost, so you could prefer the jackhammer method for that reason.

Whether you are renovating, plan on renovating, or just don’t want your home to look like a disaster zone making it temporarily unlivable, under-slab tunneling may be a great option for you. The benefit of living normally without major life disruption while having a vital repair done to your home is unmatched.

Contact us if you feel ready to get a bid for under-slab tunneling.

You now know the points under your home that need access. So if you think you would prefer under-slab tunneling as the best way to access those plumbing repairs, reach out to us for a bid

At Anchor Foundation Repair, we can expertly handle your under-slab tunneling needs with care. We do tunneling as part of foundation repair jobs, but also on its own if all you need is a way for plumbers to get under your home to complete a repair.

Although Anchor does not fix the actual plumbing issues (we let the plumbing experts do their part), we can recommend some great plumbers in the area. We love working with plumbers of integrity who understand our process and the importance of doing the job in the least intrusive and most stable way for you and your home.

Our goal is always to provide the homeowner with the best possible repair for now and with the future in mind. Along with providing excellent repairs, we also want to offer great information. If you are experiencing any signs of foundation damage or just need tunneling for plumbers to access your under-slab plumbing problem, now is the time to contact us!