Middle Tennessee sits on some of the most reactive clay soil in the southeastern United States. The clay, highly dense, high-plasticity soil, absorbs water and expands. During drought conditions, it contracts. Over the course of a few years, the cycle of expansion and contraction can exert enormous lateral and vertical pressure on underground structures. That means your foundation. Your driveway. Your retaining walls. And your pools. And if your pool isn’t designed for Middle Tennessee’s reactive clay, eventually, the ground wins.

This isn’t a reason not to build a swimming pool. Hundreds of Middle Tennessee homeowners install a swimming pool every year and enjoy them for decades without issue. But the pool you choose and the contractor you hire makes an enormous difference in whether your investment holds up or becomes a costly problem.
In this article, we’re going to give you honest education on Middle Tennessee’s soil conditions and their impact on pool construction so you can make an informed decision to ask the right questions before a shovel hits the ground.

Understanding Middle Tennessee’s Clay Soil

If you own a home in College Grove, Brentwood, Nashville, Franklin, Arrington, or the surrounding Williamson, Davidson, and Rutherford County areas, you’ve already experienced the effects of Middle Tennessee’s clay soil. Expansive clay soil are soils that contain clay minerals, primarily montmorillonite, that have an extraordinary capacity to absorb water molecules and swell dramatically in volume. Some Middle Tennessee clays can expend by 30 to 50 percent in volume when fully saturated. When they dry out, they shrink back down, sometimes pulling away from structures and leaving voids.

How Middle Tennessee’s Clay Soil Affects Pool Construction in Middle Tennessee

When you install an in-ground swimming pool, you’re excavating a large hole that’s in reactive soil, placing a structure in it, backfilling the sides, and then expecting that structure to remain watertight, level, and intact for decades. For the soil to cooperate with that expectation, three things need to be true:

  • The pool shell must be able to absorb minor soil movement without cracking or deforming.
  • The excavation and backfill must be done in a way that promotes drainage and minimizes the pressure exerted on the pool walls.
  • The pool’s design must account for the specific soil conditions present on that property.

Proper Backfill: The Critical Step Most Pool Builders Don’t Discuss Enough

The fiberglass shell is only a part of the equation. How your swimming pool is backfilled, meaning what material is used to fill the space between the pool shell and the surrounding excavated soil has an enormous impact on how that shell performs over time.

The worst backfill choice for Middle Tennessee conditions is simply using the excavated clay soil itself. This is a cost-cutting shortcut that some contractors take. Clay soil packed back around a pool shell amplifies every negative characteristic: poor drainage, high expansion pressure, and uneven settling.

Best practice is to use gravel that promotes drainage and minimizes the pressure differential between the wet and dry states. This backfill practice isn’t universal in the industry; it’s something you should ask your contractor before you hire them.

At Aviva Pools Nashville South, proper backfill selection is non-negotiable part of our installation process in Middle Tennessee. We’re happy to explain our approach and we document it.

Good Drainage Management for Middle Tennessee’s Clay Soils

An experience pool contractor in Middle Tennessee should address drainage as a standard part of the installation scope. The specifics should include:

  • A gravel drainage layer around the pool shell that promotes water dispersion rather than accumulation.
  • French drains or perimeter drainage channels on sites with known water management challenges.
  • Hydrostatic relief valves or sump pumps to allow groundwater to be released rather than push the shell upwards.
  • Proper grading of the surrounding deck and landscape to direct surface water away from the pool excavation.

These measures shouldn’t be overlooked by the pool contractor, nor the Middle Tennessee homeowner as they’re how you protect your investment against the soil conditions that are specific to Middle Tennessee.

Why Fiberglass Pools Are Recommended for Middle Tennessee’s Clay Soil

A fiberglass swimming pool is engineered to flex which allows it to absorb minor movement without fracturing. When the soil around your swimming pool expands after heavy rain, it exerts lateral pressure on the pool walls. A fiberglass shell, unlike a gunite or shotcrete, can distribute and absorb that pressure across its entire surface since the material isn’t rigid.

Middle Tennessee winters are mild, but we average 20 to 30 nights per year below freezing, with occasionally hard freezes. Freeze-thaw cycles are one of the leading causes of concrete pool surface deterioration and shell cracking in regions with reactive soils like Middle Tennessee.

Fiberglass pools are genuinely better suited for Middle Tennessee’s soil conditions than concrete pools. That’s not marketing, it’s structural engineering and real-world performance data. The flexibility of the shell, the non-porous surface, the single-piece construction, and the adaptability to proper backfill and drainage techniques all equate to a pool that better performs in this region.

But the shell is only as good as the installation. A fiberglass pool installed by a contractor who uses improper backfill, ignores drainage, or skips the site assessment is a problem waiting to happen. This is why who you hire matters as much as what you buy.

At Aviva Pools Nashville South, soil and drainage assessments are standard parts of every consultation, not because we want to complicate the process, but we know how critical these factors are to your pool being a source of joy or a headache.

Every lot in Middle Tennessee is different. Our team will visit your property and give you an honest evaluation of what’s possible with no pressure and no obligation. We’ve installed fiberglass swimming pools across College Grove, Murfreesboro, Arrington, Nashville, Brentwood, and the surrounding area, and we know the ground beneath your feet.