Under Slab Tunneling Cost in San Antonio

Under-slab tunneling is priced by the foot, and the foot rate moves with the conditions the crew has to dig through. That is why nobody quotes a run off a phone call the way a pier count gets quoted off an elevation survey. Somebody has to walk the perimeter and measure the reach first. Here is what actually moves the number, so you can read a tunneling estimate and tell whether it was scoped or guessed.

Why tunneling gets quoted by the foot

A tunnel under a slab is dug by hand. No trencher fits under a foundation and no backhoe reaches the middle of a floor plan, so a crew works the face with short tools and moves every shovelful back out the way it came. Each foot of bore gets dug once, hauled out once, held open through the repair, and filled back once. Double the run and you roughly double all four.

That is why footage is the unit. It also explains why two tunnels of the same length land in different spots on a bid sheet. Footage sets the floor of the number. Conditions set what each foot costs to produce.

Run length moves the estimate more than anything else

The length that counts runs from the point where a crew can enter the ground to the point where the work happens, not from the street or the property line. A drain failure a few feet inside the perimeter is a short reach. A master bath in the middle of the floor plan is a long one, and the bore passes under grade beams on the way there.

So a real scope starts with a locate. A plumber's camera or a hydrostatic test puts the failure at a measured distance down the line instead of a room name, and that measurement is what the estimate gets built on. If you are still guessing where the leak sits, read what a hydrostatic plumbing test tells you before you shop tunneling bids.

The entry point matters as much as the distance. Two short bores from opposite sides sometimes beat one long one, and that call gets made standing in the yard, not on a map.

Depth and soil decide how hard each foot is

The bore starts below the bottom of the footing and stays under the slab the whole way in, so the entry pit drops past the foundation before the tunnel turns horizontal. A deeper footing means a deeper pit, more spoil moved before the horizontal work begins, and more wall to keep standing while the crew is inside.

Then there is what sits in the ground. Central Texas hands crews everything from soft dark clay that shovels fast and holds a wall poorly, to caliche and limestone that holds a wall beautifully and fights every inch. Rock is the biggest single swing in hand-tunneling productivity, and a quote that prices a clay run and a rock run the same was not scoped on site. Groundwater is the other swing, since a bore that has to be pumped runs slower than a dry bore all day.

We read the soil under the specific address rather than guessing from a zip code. What is mapped under Bexar addresses, clay and rock both, is laid out on the Bexar County service area page.

Surface access and where the spoil goes

Everything above the tunnel is its own line. A crew needs room to open an entry pit, stage material, and move dirt out. A wide side yard with a gate makes that easy. A four-foot side yard fenced on one side with an air conditioner parked in the middle of it does not.

Spoil is the part homeowners never picture. Every foot of bore produces dirt that has to go somewhere, and on a tight lot it goes into bags or onto sheeting instead of a heap a machine can scoop. Bagging keeps walkways open and speeds the final backfill, and it also costs more labor than a pile. Haul-off is its own cost on top of digging, and it scales with the same footage. Texas 811 locates get called before any of it.

Backfill and restoration close out the bill

Closing a tunnel costs real money, and it is where a cheap bid usually hid the difference. Fill shoved back loose compresses under its own weight, the ground over the tunnel drops, and the slab, walk, or driveway above it cracks a year later. Backfill placed and compacted in measured lifts prevents that, and it takes time per foot the same way digging does.

Restoration is the visible half of the close. A sidewalk panel, a slice of driveway, river rock, sprinkler lines, sod, and mature landscaping all get counted twice, once coming out and once going back, and our own crews pour the concrete where a panel had to be removed. The full scope of closing an access properly is on tunnel backfill, compaction and cleanup.

The test that tells you whether that half of the bill was worth paying is not the invoice. Six months out, go stand on the ground over the tunnel after a hard rain. If it is level with everything around it, the money went where it should have.

Where the tunnel bill meets insurance and the pier bill

Two overlaps come up on almost every tunneling call. The first is insurance. A slab leak writes three separate bills, fixing the pipe, reaching it, and repairing what the water damaged, and a Texas homeowners policy treats each one differently. The tunnel is that middle bill, the access, and it is worth asking your carrier about by name instead of filing it under general repairs. Sudden accidental discharge is the classic covered loss and the worn-out pipe usually is not. Photograph the open access before it gets closed, keep the plumber's findings in writing, and confirm what your own policy says with your carrier in writing. The bucket-by-bucket walkthrough is in does homeowners insurance cover slab leaks, and the repair order once the pipe is fixed is in foundation repair after a plumbing leak.

The second overlap is the pier bill. When a tunnel exists to reach interior pier locations rather than a pipe, the pier price does not move with the access method. Steel and hybrid piers run $600 to $1,000 each installed whichever direction the crew came from, and they carry a lifetime transferable warranty. The tunnel sits beside them as its own line. Most repairs never need one, since perimeter piers install from pits dug outside the wall. Whether a small floor opening beats a tunnel on a given house is worked through on when a floor opening beats a tunnel.

How to get a real number instead of a range

Everything above is a driver, not a price. Tunneling quoted by the foot under conditions nobody has looked at is a guess with a dollar sign on it, and the fix is a visit. Ours is free.

Our ICC-certified inspectors walk the perimeter, find the workable entry, measure the reach, check the footing depth and what the soil is doing, and count what has to come out and go back. If the question is structural, the elevation survey runs at the same visit, and about a third of our inspections end with no repair needed at all. If the question is plumbing access, we scope the dig and your licensed plumber prices the pipe work, because we sell the access and never the licensed repair. The service itself is on under-slab tunneling, and plumbing companies subcontracting the dig can read the trade version on under-slab tunneling for plumbers.