Excavator digging a basement hole into red clay and limestone on a hillside lot

05 · Excavation

Excavation in Nashville: basements, footings, pads and ponds

“From basement digs to utility trenching,” excavation is digging to a shape somebody drew: a depth, a footprint, a grade. Here’s how that goes in Middle Tennessee ground.

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Dug to the plan, plus working room

Every dig starts with stakes. The plan sets the footprint and the bottom elevation, and the hole is cut a little wider than the walls so the foundation crew has room to set forms and waterproof. Footings go down to firm, undisturbed soil. If the bottom of the hole turns out soft, it gets dug out further and rebuilt with stone rather than poured over.

Ponds and detention basins are shaped differently. The side slopes and the outlet matter as much as the depth, and a dam or berm has to be built up in compacted layers from soil that will hold water.

The dirt has to go somewhere

Soil swells when it comes out of the ground; a basement’s worth of clay takes up a lot more room loose in a pile than it did in place. Some of it goes back as backfill around the walls. The rest is spread on the property, used to build up a low yard, or loaded and hauled. Deciding that before the dig starts keeps the lot from turning into a mud pile.

Rock: how far down it starts

Bedrock can sit close to the surface around Nashville. A USGS study of Middle Tennessee put the median depth to bedrock at 2.4 meters, about 8 feet, in the inner Central Basin and 3.7 meters, about 12 feet, in the outer basin, against roughly 15 meters on the Highland Rim. Those are regional medians, not a reading for your lot. A basement dig can hit ledge rock a few feet down or never touch it, and rock changes both the method and the price.

Water in the hole

Groundwater and rain both end up at the bottom of an excavation. A sump in one corner and a pump keep a footing trench workable after a storm, and a basement on a wet site often gets a perimeter drain before the walls go up. The sides of a cut also lose strength when they’re wet, which is why a deep hole gets its walls sloped back or braced instead of left standing straight.

Three working days’ notice to Tennessee 811

Tennessee 811 says anyone who digs, homeowners included, must give at least three working days’ notice before starting so the member utilities can mark their lines. A ticket is good for 15 calendar days after the start date it requests, and a dig that runs longer needs an update requested three working days before the ticket runs out. Basement jobs can outlast one ticket, so the renewal goes on the calendar at the start.

What this covers

Basement digs
Footings and pads
Spoil moved or hauled

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Answers

Questions about excavation

How much does it cost to dig a basement?

Basement excavation is priced on the volume of soil and what happens to it. A deeper or larger footprint means more cubic yards; hauling the spoil off costs more than spreading it on the lot; rock, groundwater and tight access all add time. An estimate needs the foundation plan, or at least the footprint and the depth.

What happens if you hit rock during excavation?

The method changes. Soft or broken rock can often be ripped out with the excavator, while solid ledge has to be broken with a hydraulic hammer, which is slower and costs more. Sometimes the better answer is raising the floor elevation or adjusting the design so the dig stays above the rock.

How long is a Tennessee 811 ticket valid?

Fifteen calendar days after the legal start date on the ticket. When digging will run past that, Tennessee 811 asks for an update request three working days before the ticket expires so it never lapses in the middle of a job. The original request has to go in at least three working days before digging starts.

What is the difference between excavation and grading?

Excavation digs down to a set depth and shape: a basement, a footing, a trench or a pond. Grading moves soil across the surface to set elevations and slopes over a wider area, such as a building pad or a yard. Most building sites need both, with grading done around and after the excavation.

Can excavation be done in the rain?

Light rain usually doesn’t stop a dig; heavy rain does. Wet clay turns slick under tracks, the bottom of a footing trench softens, and the walls of a deep cut lose strength. Work generally pauses until the hole is pumped out and the ground firms up, since pouring a footing on mud costs far more than a day’s wait.

What happens if you dig without calling 811?

You risk striking a buried line nobody marked. Tennessee 811 says damage incidents can mean millions of dollars in property damage, interrupted utility service and personal injury, and the state’s Underground Utility Damage Prevention Act requires everyone who digs, homeowners included, to give notice first. The service is free.

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