how long does tunneling take?

How Long Does an Under-Slab Tunneling Project Take from Start to Finish?

You’re thinking about using Anchor Foundation Repair to do an under-slab tunneling project to get plumbing issues repaired under your home. Or maybe you’re already signed on for tunneling work and want to know what to expect as far as time goes. Just how long does this under-slab tunneling stuff take?

Anchor Foundation Repair Bryan College Station

At Anchor Foundation Repair, we’ve been tunneling under houses for longer than we can remember. Under-slab tunneling is one of our specialties so we can certainly tell you about our process.

This article will detail Anchor’s under-slab tunneling process with attention paid to approximating timelines. Although every job is as different as every home, we can help let you know approximately how long it takes based on our 35+ years of experience doing this kind of work.

What Is the Under-Slab Tunneling Process?

how long does it take for under-slab tunneling?

Before we dive into the complete time an under-slab tunneling project takes, it helps to understand the steps of the process. It’s not just digging a tunnel and you’re done, there’s more to it so we break it down into phases.

Phase 1: Digging the Tunnel aka Excavation

Phase 2: Plumbing Repairs

Phase 3: Backfill and Mud Pumping

Now let’s talk more about what happens in each of these work phases so that you fully understand what’s going to happen at your home when Anchor is in charge of your tunnel.

Phase 1: Digging the Tunnel aka Excavation

During the excavation phase, we first need the right starting point for the tunnel. We will likely already know where your plumbing lines need repairs. The starting point will be chosen to make for the shortest tunnel to reach the repair point and follow along your drain line system. 

under-slab tunneling is hard

The hardest part of digging a tunnel is the beginning because we have to dig down to get under the concrete perimeter beam of your home. For some homes, the beam depth can be significant perhaps 6 feet below the ground.

We dig straight down to get under the beam and then have to dig straight up on the other side of the beam to reach the underside of your slab. For safety and to prevent cave-ins, the underside of your concrete foundation serves as the “ceiling” of our tunnel.

Digging is done primarily by hand with shovels and electric shovels. Moving the dirt out of the tunnel is also done by hand with small tools. We don’t use large machinery because we need to protect the structural integrity of your home. We’re digging carefully and making sure that no other lines or infrastructure get damaged during excavation.

Digging tunnels is hard, slow work. Plumbers don’t like to do it, so they often prefer that Anchor does it for them instead. The result is a neatly done 3 ft by 3ft square tunnel that a plumber can easily move around in to reach and repair your plumbing lines.

Phase 2: Plumbing Repairs

Anchor does not fix your under-slab plumbing issues. We leave that to the professional plumbers. But we work with plumbers in the area all the time and will coordinate with them to make sure they start your repairs ASAP once the tunnel is ready.

repair under-slab plumbing with tunneling
Nicely repaired under-slab plumbing

We won’t be on-site during this time to allow your selected plumber to do his job. When we return, we do check to make sure the plumbing repairs meet appropriate standards for under-slab environments. If you’re using a plumber that we work with often, this isn’t an issue. 

If the plumber has not yet done so, we will also conduct a hydrostatic pressure test to ensure there are no further leaks in the plumbing. We can’t move to the next step until we confirm that there are no other breaks in the lines.

Phase 3: Backfill and Mud Pumping

Phase 3 is an important yet often forgotten step of the process. Filling the tunnel back in should be done with a lot of intention, and should not be an afterthought. Your home is on top of this tunnel. A tunnel needs to be filled in correctly to optimize the support of your home and to help prevent foundation settlement.

under-slab tunneling process
Not gonna reuse this clay . . .

First, we bring in loose topsoil backfill. We do not reuse the old expansive clay soil that was removed from under your home, but some of the select fill used during the construction of your slab may be reusable. At the same time that the loose backfill and any salvageable soil is being packed into the tunnel, we are also laying the *groundwork* for mud pumping by inserting PVC piping along the tunnel’s path.

The pipes are strategically placed throughout the tunnel and will carry a pressurized slurry mixture to further secure the area. The liquid slurry, made from topsoil, Portland cement, and water, is pumped under the home and fills in all the air gaps and space where the tunnel once was. The slurry then dries and hardens into a sandstone-like consistency.

Using mud-pumping ensures that the previous tunnel is completely filled and fully secured, and is far superior to just using dirt. This is an extra step that many other companies choose not to take. But we know it’s the absolute best situation we can create for your home.

How Much Time Does Each Step of Under-Slab Tunneling Take?

Now that you understand what each phase of the process entails, I bet you want to know how long each step takes. So let’s get to it!

Time for Phase 1: Digging the Tunnel aka Excavation

In general, we can dig between 6 and 8 feet of tunnel per day. The best-case scenario is about 12 feet in one day if conditions are perfect.

So let’s say you need 16 to 18 feet (a medium-sized job) of tunneling for your repairs, then probably plan on 2 to 3 days’ worth of digging.

under-slab plumbing repairs via tunneling

Time for Phase 2: Plumbing Repairs

The amount of time for plumbing repairs can vary depending on how many lines and/or breaks need repairing. We’d say that about 2 to 3 days of plumbing repairs is a conservative estimate. If you need the entire home’s drain lines redone, then it could take about a week or more for the plumbing repairs.

Time for Phase 3: Backfill and Mud Pumping

During the backfilling and mud pumping phase, it usually takes about as long to do the filling as it did to do the digging as a general rule. So if it took 2-3 days to dig, then it will take 2-3 days for backfill and mud pumping.

How Long Does an Average Under-Slab Tunneling Project Last?

We’re not mathematicians, but we at least know that now we’ve got to add up all these times in each phase to get a total amount of time for the job.

  • For a smaller tunneling project involving one drain line branch (like you might find in a hall bath), it could need 6 to 8 feet of tunneling. This small tunneling job would take about a week from start to finish.
  • For a medium-sized tunnel job, like the 16 to 18 feet of tunnel with a few breaks that need repairing, I’d say that could be done in under two weeks.
  • For an extensive tunneling project, where your whole under-home plumbing line system needs replacing, it could take about a month to complete.
tunneling lets you stay in your home during the repair process
Don’t worry, tunneling allows you to stay in your home mostly undisturbed . . .

Now, keep in mind that it’s not like you’re going to be without the use of your plumbing lines this entire time. 

There’s a lot of digging time that you can still use your lines. At some point, you might not have use of the lines that need work as we get closer to the repair points. 

Plumbers work on separate sections of the drain line system at a time and can often isolate the part they are working on. So you might not be able to use every plumbing fixture in your house, but some might be temporarily out of use. 

Then after the plumbing lines are repaired you are good to go with regular use of all plumbing lines, even if we still need to backfill. Does that put your mind at ease?

The Advantages of Under-Slab Tunneling

Now you know some estimated timelines, and you might be thinking, “Wow, this tunneling stuff is going to take a long time.” You’re not wrong. BUT the huge advantage of under-slab tunneling is that you can live and stay in your home as normal, even while work is going on.

under-slab tunneling is better

Think about the alternative where a plumber breaks through your slab. You’ve got dirt piled up in your house with plumbers traipsing in and out tracking dirt everywhere. Have I mentioned possible ruined flooring yet?? You might not even be able to live there due to the chaos . . .

At Anchor Foundation Repair, we understand homeowners’ stress and worry when it comes to big projects like foundation repair and under-slab tunneling. We’re here to make it easier on you by making sure you know what to expect with tunneling. Then we do the very best for your home by treating it as our own, giving you peace of mind with Anchor’s excellent work and attention to detail.

For more clarity on the vast differences between choosing tunneling over breaking your slab, check this out Under-Slab Tunneling vs. Breaking Through Your Slab (Pros and Cons).