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Thornton Engineering & Construction

“Proper maintenance of the foundation slab includes a relative constant moisture content of the soil adjacent to the slab foundation…recommend an aggressive watering program.”

John B. Thornton, P.E.

Peverly Engineering, Inc.

“The primary cause of foundation settlement is the loss of moisture from the soil beneath the exterior grade beams…The obvious cure is to maintain the soil in a moist condition.”

Richard W. Peverly, P. E.

Newman Inspectors & Engineers, Inc.

“Water liberally around the foundation…in a uniform manner around the entire house to prevent uneven soil movement.”

B. A. Newman, P.E.

Testing Unlimited Incorporated/Geotechnical Engineering

“…if the moisture content variation can be expected to remain within a reasonable narrow range, excessive problems with clay shrink-swell phenomena will be unlikely. Maintaining the moisture is the key factor.

S. N. Endley, Ph.D., P.E.

KESCORP/Knight Engineering Services
“Provided normal soil moisture is maintained during the drier months of the year, continued performance of this foundation system is expected to be as intended.”

David W. Knight, P.E.

Jack Deal Consultants, Inc.
liberal watering of soil at a time of excessive dry spells, will aid in controlling the rate of settlement…objective of the maintenance program is to control as nearly as practical, a constant moisture content of the load-bearing soil directly under the foundation at the perimeter of the building.

E. J. Deal, Jr., P.E.

Geotech Engineering and Testing, Inc.

Moisture Stabilization can be an effective method of stabilizing subsoil shrink-swell movements in the areas where expansive soils are present…In general, the purpose of the system is to stabilize the moisture content around the slab to a uniform condition; therefore, minimizing the extremes of shrink and swelling problems.”

David A. Eastwood, P.E.

The University of Texas at Arlington

“I would like to use this letter to further emphasize the necessity of soil stabilization during the process of providing long term stability of expansive clay soils is water content stabilization. It is interesting to note that…this moisture stabilizing process, when done correctly, has resulted in no need for further leveling of the structure.”

Thomas M. Petry, Ph.D., P.E.

A Study of Behavior of Slabs Founded on Active Clay Soils, Vol. 1

Writing of an experiment in watering, it was stated; “The significant result from this test was the impressive vertical movement which could occur (approximately 1 inch in 2 days) in a very short time period.”

“The swell or shrinkage of active clay soils and the amount of different movement of a slab on-ground is a function of…water availability.”

“Whenever moisture differentials exist, a suction potential develops. This potential causes moisture movement from wetter to drier regions.”

Richard L. Tucker, Ph.D., P.E. and Arthur R. Poor, Ph. D., P.E.

Foundation Repair Techniques for Residential Structures

“We do not believe that…piers (or pilings) are the only solution to level buildings, especially since the appraisers will typically devalue a property if foundation leveling has been done. We do believe that leveling piers should be the last option used to correct a foundation, only after other methods have been ruled out or are not deemed adequate.” The following methods are always used to raise a foundation system:
A) Drilled bell-bottom leveling piers
B) Pressed piles (concrete or steel)
C) Helical anchors
D) Polyurethane injection

Donald E. Lenert, P.E.

The Prediction of Soil Heave and Swell Pressures Developed by an Expansive Clay

“Pavements and slabs founded on expansive clays are subject to large differential movements caused by soil moisture changes…”

Differential suction values in a soil result in moisture movements from regions of low suction to regions of high suction. The moisture will migrate until equilibrium of the suction forces has been achieved.”

Expansive soils located in regions of prolonged hot dry periods followed by cooler wet periods cause the most problems” (The exact weather conditions that prevail in the greater Houston area.)

“After a dry period, the soils will have relatively low moisture contents resulting in high well potentials. Wetting of these soils will result in large swells.” Gary L. Schneider and Arthur R. Poor, Ph.D., P.E.

Data Supplement for Experimental Residential Foundation Designs on Expansive Clay Soils

(This treatise documents activities associated with the design and construction of single family residences and their behavioral pattern over six seasonal climatic cycles, or approximately three years. The floor slab for all houses were on highly expansive clay soils.)

“Results indicated that…raising the natural moisture content a minimum of two to three percent above the plastic limit and maintaining the moisture at this level…significantly inhibits volume changes in expansive clay soils due to seasonal weather cycles.
This was evidenced for both total vertical movements and differential movements.”

“It was concluded that adding water to a soil mass can be accomplished…This necessitates adding water slowly and causing swelling from the bottom upwards. Adding water at a fast rate or ponding would cause the surfaced to seal.”

Arthur R. Poor, Ph.D., P.E.

Soil Moisture and Temperature Variations Beneath a Slab Barrier on Expansive Clay

“Slabs-on-ground founded on expansive clays are subject to large differential movements caused by soil moisture differentials…Structurally stiffened slabs…are expensive and not entirely successful. New foundation design techniques have been hampered by lack of sufficient knowledge concerning the magnitude of possible moisture differentials and the depth of which moisture changes are significant. Instrumentation of a forty foot square slab…provided needed information concerning soil moisture variations beneath slabs-on-ground…Seasonal moisture changes were found to extend to a depth between ten to fifteen feet; however, the moisture changes in the top five feet were much more significant in causing soil volume changes.”

“Many lightly loaded structures, such as houses, apartments, small industrial buildings…are susceptible to damage in expansive clays. The loads exerted by these structures are small compared to the pressures that can be developed by the expansive clays as they imbibe moisture. The pressures that are developed cause upward movements…Other areas of these structures may experience settlement from drying of the soils.”

Since the principle problem in expansive clays is essentially one of moisture differentials, it appears that the solution to these problems may be found in methods to control subsurface moisture conditions.”

“Basically, soil suction describes a soil’s attraction for water…
The suction exerted by a soil increases with decreasing moisture content.”

“Moisture changes cause seasonal volume changes of the soil profile…95 percent of the volume changes will occur in the top ten feet and over 85 percent of the volume changes will occur in the top seven feet.”

“The effect of precipitation and evaporation on the subsurface soil moisture condition varies depending on the time of the year…the net effect of a winter rainfall is to maintain the surface in a wet condition…Precipitation during the summer months causes a somewhat different effect. During the summer months, the surface soils lose moisture through evaporation and shrink. This shrinkage frequently causes cracks to open in the soil…when precipitation falls on the surface…
It appears that the magnitude of the precipitation during the summer would be insufficient to close these cracks except perhaps near the surface” (and thus “seal” the ground to penetration and give-up more precipitation to run-off).

Robert C. Davis, Ph.D., and Richard L. Tucker, Ph.D., P.E.

House Damage from Clay Soil and Climate

“…foundation problems are produced by one or more of the following factors:…Homeowner fails to provide good maintenance for the foundation; over waters, under waters, or does not water evenly; plants trees too close to the house; changes the designed drainage system of the house by bedding for flowers and shrubs…”


Arthur R. Poor, Ph.D., P.E.

Experts have this to say…

Does watering my foundation help prevent foundation problems?

…”If your house is built over clay sub-soils, the key to maintaining your good foundation is to maintain the stability of the water content in your soil.
Rapid changes from too much water to a dry condition in the clay, and visa-versa, cause great stresses to be exerted on the foundation… Trees are generally considered beneficial to the value of a home, but trees located too close to the foundation can dry out the soil, causing the soil to shrink.”

Susan Quiring, Ph.D.
Robert O. Segner, Jr., A.I.C.
Carrol D. Claycamp, P.E., A.I.C.
Charles J. Goodwin, P.E.
Texas Agricultural Extension Service
Texas A&M University System

…”It is important that watering be conducted in a systematic and scheduled manner…to maintain moisture stability and uniformity, and prevent volume changes for the clay soil. As a benefit, the grass and landscape will thrive.”

Judith B. Corely
J. H. Marsh III
Susan M. Quiring
Charles J. Goodwin, P.E.
Texas Agricultural Extension Service
Texas A&M University System

…”The homeowner’s responsibility for maintenance is of first importance to successful foundation performance. More than any other single factor, maintenance, or lack or it, determines the useful life of the house. Foundation maintenance, in general, consists of just one major idea:
The moisture content of the soil in the entire area covered by the house should be as constant and uniform as possible at all times.
If you have foundation damage in your home… Do not repair the damaged areas until you have found and removed the cause. Just as you do not want to take a pain reliever for a bad stomach ache until you find out if it is caused by appendicitis,
you should not cover up the symptoms of foundation trouble until you have corrected the foundation defects.
If you do not stabilize the soil before making the repairs your time and money is wasted because they will not be permanent, and you will be covering up the conditions which will indicate to you that your home is in danger—from fire hazards, as well as deterioration…

Arthur Poor, Ph.D., P.E.
Professor of Civil Engineering
Construction Research Center
Arlington, TX 76019