under-slab tunneling process

How Does Under-Slab Tunneling Work? Basic 5 Step Process

You’ve heard about under-slab tunneling. You are *most intrigued* by the idea that it keeps all the plumbing repair mess outside your home. You are *even more intrigued* about the idea that under-slab tunneling does not compromise or break up your slab foundation in the process. Same here . . . 

Anchor Foundation Repair

But what is the process exactly? How does a tunneling crew go about doing their tunneling thing? Good question.

At Anchor Foundation Repair, we dig under-slab tunnels all the time and have dug over 1,000 tunnels in our 35+ years in business. We know about all the right ways to complete this kind of work and can tell you all about it.

This article will review the 5 step process for planning, digging, and filling a tunnel used to access and repair leaks under your slab-on-grade foundation.

What’s So Great About Under-Slab Tunneling Again?

under-slab tunneling prevents this mess

Here’s a *tiny refresher* on what under-slab tunneling is and what is positive about using under-slab tunneling. Just in case you missed it earlier . . . 

Under-slab tunneling is an alternative to breaking through a slab foundation from above to reach and repair under-slab plumbing leaks. Tunnels allow a plumber to repair leaking drain lines under your home without coming inside your house. 

This is awesome because it keeps all the chaos, mess, and people outside and underneath your home instead of on the *inside part* where you like to live. Tunneling allows you to keep using your home nearly normally even while repairs are in progress. Sounds pretty good, huh?

5 Steps in the Under-Slab Tunneling Process

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 so that’s really the first step. Let’s check out the whole process, shall we?

Step 1. Determine Tunnel Location to Reach All Plumbing Failures

planning an under-slab tunnel Bryan College Station

It’s important to know where the plumbing is failing. All tunneling jobs depend upon reaching a particular location or locations under the home.

A plumber would typically be the one to figure this out if under-slab leaks are your only repair issue. However, if the under-slab leaks were discovered or are part of a foundation repair project, the foundation repair team can also be the ones to determine where the problem points are located.

Performing hydrostatic plumbing tests and a process of elimination can help isolate the location of the leak(s). Hydrostatic testing fills up your drain lines with water and then sees if they hold that water. 

If the section of line being tested leaks, then the plumber or team can figure out where the plumbing needs repair. There could be just one spot that has a leak, or several in different sections of your drain line system.

Step 2. Plan the Path of the Tunnel(s)

tunneling path diagram

Once the location of the leak has been isolated, a path can be planned for the tunnel. A tunneling team will want the shortest, straightest tunnel from the edge of your home heading to the repair location. The tunnel path will typically follow the same route as the drain line path.

The starting point of the tunnel will be the outside edge of your home closest to the leak and head under the house. Sometimes the starting point has to be adjusted if there is something in the way like a tree, sidewalk, or A/C unit. 

The tunneling team will make every effort to keep the tunnel as short as possible. Shorter tunnels save time, and shorter tunnels save the homeowner money since the tunneling cost is priced per foot.

Step 3: Dig 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 several feet 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.

tunneling to repair under-slab leaks

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 after reaching the underside of the slab 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.

Commentary on Who Should Be Digging These Kinds of Tunnels

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 easily and efficiently. If someone who has no idea what they are doing tries to tackle it, they begin to see that digging in expansive clay soils is too much for someone without experience.

True story: 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 4: Repairing the Plumbing Problem

under-slab plumbing

No matter who locates the leaks or digs the tunnel, it’s going to be a plumber that needs to fix the leaking lines. So the plumber will do their thing and the tunneling crew will wait until the repairs are done.

So, a plumber will come to complete the repairs. You would want to make sure that they are comfortable with working in a tunnel, as some may not have that expertise. If you do not have a special plumber in mind, we can also recommend plumbers that have experience with under-slab tunnel work.

A tunneling 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 again 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 and home in general.

Step 5: Filling in the Tunnel

So the repairs and pressure testing have proven successful and the system is *leak-free*. The tunneling crew will then return to fill in the tunnel correctly, using both the removed dirt as well as new dirt as needed. 

digging a tunnel BCS

Filling a tunnel back in properly is more important than how it was dug in the first place. This is where the expertise of having a foundation repair company do the tunneling comes into play.

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 (called slurry) with pressure under the slab.

Filling in the Under-Slab Tunnel Properly Is Really Important

under-slab tunneling in BCS

The finishing process using mud-pumping makes sure that even the smallest pocket of space is filled and provides proper support under your concrete slab foundation. The 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.

At Anchor Foundation Repair, we do under-slab tunneling with many of our foundation repair projects because taking care of leaks is just as important as filling the tunnel properly. Having one repair team take care of both aspects of the project ensures continuity in the treatment of your home.

Read about all the ways that mud-pumping with slurry is beneficial in this article: “How is Slurry Used in Foundation Repair, Concrete Repair, and Under-Slab Tunneling?