fill the tunnel

The Best Way to Backfill an Under-Home Tunnel + What If You Skip It

You’ve got a leak in the plumbing under your home and you’ve already decided to handle that with under-slab tunneling. Good call. Now that you’ve made that decision, you’re faced with another decision and even more questions: 

  • Should the tunnel be filled in afterward or not? 
  • Does it even matter? 
  • What could happen if the tunnel remains unfilled?
  • While we’re at it, what’s the best way to fill a tunnel anyway?
Anchor Foundation Repair Bryan College Station

At Anchor Foundation Repair, we understand the stress and anxiety (and all the questions) that come with overwhelming repair projects. We specialize in under-slab tunneling services and have dug and backfilled thousands of tunnels under Brazos Valley homes in the past 35+ years. 

We can *fill* you in on all the *dirt* about backfilling . . . sorry, puns just sort of come with the package . . . 

This article discusses the best way to backfill tunnels under your home and why. We’ll list out the potential consequences if you don’t do the backfilling as recommended. Then, we outline the timelines and costs associated with the type of tunnel backfilling we can provide here at Anchor Foundation Repair.

Do I Need to Fill In Tunnels Dug Under My Home?

There are many times that tunnels are not filled back in after under-slab plumbing work or foundation repairs, but those are other companies and contractors making those decisions. For some reason, they don’t think it’s needed and/or not their problem or part of their job to handle. 

large tunnel space should be backfilled and mud-pumped
Dude, this tunnel is sizable and should be filled back in.

We won’t be shy about saying that it’s just wrong and not the best way to leave a home post-tunneling. We strongly recommend the best practice of backfilling the tunnel both with new dirt as well as with mud-pumping to fill and secure the void under your home after tunneling. 

A slab-on-grade foundation is designed to sit on dirt – it’s literally in the name. The term “on-grade” is a fancy construction-y way of saying *slab on the ground*. When you take away the *grade* from underneath a slab, it ain’t *on it* no more. How can that be a good thing?

So, I will boldly say “yes” – you need to and should fill in the tunnels dug under your home. If no one takes the time to refill the tunnel, nature will find a way to fill it with something (and it won’t be good). We’ll talk more specifically about the best way to refill a tunnel a little later on.

What Happens If Under-Home Tunnels Are Not Backfilled?

A slab home that is not resting on the ground as intended presents a major opportunity for foundation settlement and other problems. Foundation settlement can lead to foundation problems with major repairs costing thousands of dollars.

Issues that seem minor at first can cascade into the big problem of foundation settlement. Conditions deteriorate slowly over a number of years. You could easily be unaware that it’s even happening. It might go something like this if you don’t get your under-slab tunnels backfilled and mud-pumped as recommended:

you should fill in tunnels under your home
Hard to see, but this is water we had to pump out from under a slab.
  1. The tunnel start hole caves in a little,
  2. Water accumulates in the caved-in area and eventually works its way under the slab,
  3. More water intrudes under the slab every time it rains,
  4. Dirt erodes more and you start seeing gaps and holes in the soil around your home
  5. Your floors might start to sound or feel more hollow (if they didn’t already),
  6. Rainwater pools under your home regularly,
  7. One day, your home sinks and you now need foundation repairs.

Now, there’s no guarantee that this always happens, but it’s a significant risk. Water goes where it wants, flows to the lowest point, and is difficult to control. Never underestimate the effects that even small amounts of water can have when given enough time and a path.

What Is the Best Way to Backfill Under-Slab Tunnels?

After your under-slab plumbing repairs are completed properly, backfilling the tunnel with fresh topsoil is a good start. But backfilling with soil alone has its limitations. There will be air pockets and packing the dirt can be difficult in the confined space. There’s only so much a guy under your house can do by hand to refill the tunnel.

slurry for mud pumping and filling tunnels

Mud-pumping the tunnel adds another dimension of void-filling capability that surpasses what plain ol’ dirt can do. In a nutshell, mud-pumping uses a flowing pressurized mixture of water, topsoil, and cement (called slurry) that is pumped throughout the tunnel to fill in all air gaps and space. 

The slurry mixture dries and hardens to the consistency of sandstone offering more stability and support than plain dirt to fill and support the space that was once a tunnel.

We’ve got several other articles detailing the mud-pumping concept and the mud-pumping process that you can check out too. Essentially, doing tunnel backfill with mud-pumping offers these benefits after under-slab tunneling and foundation repairs too:

  • Restores optimal support to the underside of the slab after plumbing repairs,
  • Prevents cave-ins of the tunnel’s starting hole and the effects of erosion and runoff,
  • Prevents pooling water under your home,
  • Prevents the feel of hollow-sounding floors,
  • Keeps big burrowing critters from gaining easy access under the slab,
  • Minimizes the chance of future slab settlement in the area of the previous tunnel.

This is not to say that mud-pumping your tunnel is a 100% failsafe guaranteed to prevent any and all settlement, but it offers you the best conditions for heading off potential problems.

How Much Time and Cost Does Backfilling Add to My Project?

As you might expect, the mud-pumping process does add some time and additional cost to your project. It could take between ½ day to 3 days to complete topsoil backfilling plus mud-pumping and it depends on the length of the tunnel.

mud-pumping is the best way to backfill a tunnel

Backfilling a tunnel is hard work that takes time because it all has to be done by simple manpower working in small spaces. As they are bringing in the new soil, they are also laying the *groundwork* for the mud-pumping process with a series of pipes to bring in the pressurized slurry.

Added costs for proper backfilling and mud-pumping could range from $1,000 to $6,000 or more. Again, the costs depend on the length of the tunnel and also the depth of the perimeter concrete beam around your home. If your beam is really deep, a lot more soil has to be moved and packed in to refill the tunnel. 

Who In the Brazos Valley Does Proper Backfilling?

under slab tunneling and best backfilling methods
We can fill this tunnel, yo . . .

Now that you know how a tunnel should be properly backfilled with mud-pumping and why, I’m sure you want to know who can do this for you. Well, good news . . . we can!

At Anchor Foundation Repair, we don’t fix things that don’t need fixin’, and we don’t try to sell you stuff you don’t need. After 35+ years in business, that’s what’s best for our Brazos Valley community and for exceptional homeowners like you. 

We believe that mud-pumping is the best thing you can do to care for your home after tunneling. That’s why you need it and that’s why we do it. Want to know more details about having tunneling and mud-pumping done on your property? Check out What to Expect from an Under-Slab Tunneling Project on Your Home.