Some of the most confusing water damage calls we take have no obvious source. Floors feel warm or damp, baseboards swell, and nothing is dripping from the ceiling. When a house sits on a concrete slab, the water can be coming from a line under the floor, out of sight. Ground movement is one of the reasons those lines fail, and North Texas has a lot of ground that moves. This post explains what engineers who work on North Texas foundations say about expansive clay, and how that movement can end up as water inside a home.
A quick note on scope. The engineering sources we use below write about Texas and the Dallas area. We did not find an Azle-specific soil study, and soil can change from lot to lot, so treat this as background and not as a statement about your particular yard.
What expansive clay is
Datum Engineers, a Dallas geotechnical firm, opens its booklet Designing Structures in Expansive Clay by saying that expansive clay soil is common to many parts of Texas and has caused significant structural damage to an alarming number of buildings. The firm adds that the pressures generated by swelling clay can be devastating to a foundation if not managed correctly. Clay swells when it takes on water and shrinks when it dries, and that cycle is what moves things built on top of it.
How deep the movement goes
Reed Engineering Group, also in Dallas, published a paper on foundation distress called Lessons Learned from Distress of Foundations on Expansive Clays in the Active Zone. It describes the “active zone” as the soil depth where moisture changes with the seasons. Citing earlier research, the paper says the depth of the seasonal active zone was reported as 7 to 15 feet in Dallas. It also gives the average annual rainfall for the Dallas area as 33 inches.
Those two facts explain a lot. Rain does not arrive evenly. Wet spells and dry spells swing the moisture in the top several feet of soil, and clay responds to every swing. The paper also notes that leaking utility lines can change the depth of moisture change, which means a leak can feed the same movement that is stressing the pipe.
What that does to a slab house
A slab-on-grade foundation is a concrete slab cast directly on the ground. Datum’s booklet, which is written mainly about commercial buildings, says slab-on-grade construction carries a higher risk potential for damage by expansive soils because the floor slab is cast directly on the ground. In one of the internal memos reproduced in the booklet, an engineer warns that pipes laid in expansive clay are subject to movement as the clay expands, which can lead to broken pipes. The same logic applies to the lines under a house.
For a homeowner, the practical point is that water supply lines and drain lines often run through or under the slab. If soil movement flexes or shears one, the line can leak into the ground below the house or into the space under your flooring. Because the water is hidden, it can run for a long time before anything shows on the surface.
How hidden water travels
Datum also describes how water moves along buried pipes. Its booklet says that many underground pipes installed during construction enter and exit beneath the building, creating hidden conduits for water infiltration. Often they are surrounded by loose backfill, such as gravel or sand, which collects water and lets it flow along the trench and under the foundation. The authors say this type of water infiltration has caused many slab problems and can easily go undetected.
Reed’s paper describes a case where water-bearing sand in a utility trench carried water along the line, and the largest heave in that building was found over the line and near planter beds. Water that has a path can go a long way from where it started, which is also why a floor can get wet in a place far from the break.
Signs worth acting on
We cannot diagnose a slab from a web page, and we do not repair the lines themselves. But these signs are worth a call:
- Floors that feel warm or damp in one area
- Baseboards that swell or flooring that cups or lifts without an obvious spill
- The sound of running water when everything is off
- A water bill that climbs without a change in use
- New cracks or sticking doors, which can signal soil movement
What we do and what we do not
When water from a slab or line failure gets into a home, our team handles the water side. We use moisture meters to find where it went, extract what we can and dry the structure so the damage does not keep spreading. See our water damage restoration in Azle page for the full process and water extraction in Azle for how we pull water out of carpet, padding and flooring. The failed line itself needs a pipe repair contractor, and the cause of soil movement needs a foundation or geotechnical specialist. We can tell you what we found so they know where to look.
If you suspect a hidden leak, contact Water Damage Azle or call. Our line is answered 24/7.
Sources
- Datum Engineers, Designing Structures in Expansive Clay (PDF)
- Reed, Tand and Vipulanandan, Lessons Learned from Distress of Foundations on Expansive Clays in the Active Zone (PDF)