Living With Expansive Soils

A GUIDE TO FOUNDATION MAINTENANCE
by Marshall B. Addison, PHD., P.E.
Consulting Geotechnical Engineer
University of Texas at Arlington,
Civil and Environmental Department Box 19308, Arlington, Texas 76019-0308

Living with Expansive Soils
Expansive soils can create damaging movements shrink and swell to foundations and structures. These movements originate from changes in soil moisture. Providing uniform soil moisture next to and under your foundation is the single best thing you can have to reduce or minimize the effect expansive soil movements have on your structure.

Indicators of Expansive Soil Movements
The items below are signs you can look for to determine possible expansive soil related movement. The probability that your foundation has experienced some movement increases with the number of indicators observed, their frequency and location in the structure.

Exterior Indicators:

• Diagonal (stair-stepping) Cracks in brick walls. Cracks may go through brick or mortar and vary in width.

• Sagging brick lines when sighting along a wall.

• Bowed or non-vertical walls.

• Separation of wood trim joints at corners.

• Separation of concrete driveway, patio, or sidewalk from foundation.

• Tilting of landscaping/retaining walls.

Interior Indicators:

• Cracks in sheetrock walls or ceilings.

• Bowed or non-vertical walls.

• Bottom of wall separating from the floor.

• Cracks at wall corners.

• Cracks above doors.

• Sticking doors. (warped door frames)

• Sticking windows.

• Sloping floor surface.

• Cracks in ceramic or vinyl tile.

• Cracks in concrete floor 1/16th inch across or wider.

Soil Moisture Changes
Observing soil moisture changes around your foundation is possible, but what about under it? Moisture can move from outside to under your foundation through a property of soils known as suction. Soil suction is similar to placing just a corner of a dry, compressed sponge in contact with a puddle of water. In a short time, the sponge has drawn water throughout itself and grown in volume. While a water source is present, the sponge will continue to absorb water until it is saturated. If the water source is cut-off, then water already in the sponge will distribute itself evenly, but the sponge will not reach saturation.

Water can move horizontally and vertically through the soils under your foundation in a similar manner. As clayey soils draw water to themselves, they too grow in volume (swell or heave) causing your foundation to move. Drying outside your foundation reverses the process. The moist soils will lose volume (shrink) as soil moisture moves out from under your foundation causing the foundation to settle. Shrinking and swelling soil motions can lead to damaging your foundation and structure. Uniform changes in soil moisture are less damaging to your structure than localized changes.

Several sources of soil moisture changes are provided in the following table. You should review the list and possible actions to control or minimize the various sources. Begin practicing the suggested actions as soon as possible to improve your foundation and structure performance. Many of these actions can become a routine part of your ongoing conscientious owner maintenance activities. Annually inspect the area within 5 feet of all sides of your foundation after a rain to determine if proper drainage is maintained away from your structure. Monitor existing cracks for progressive or seasonal movements. Some of the possible actions, suggested in the accompanying table, will require an expert for assistance. Additional information on all of these items can be obtained in the excellent reference, So Your Home is Built On Expansive Soils, A Discussion of How Expansive Soils Affect Buildings, edited by Warren Wray, Ph.D., PE., published in 1995 by The American Society of Civil Engineers. This 54 page booklet can be obtained for approximately $20.00 by calling ASCE publications at (800) 548-2723.