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Expansive Soil Stabilization

John Huang, Ph.D., PE and John Poullain, PE

This four hour online course discusses guidelines and criteria for modifying and stabilizing expansive clay soils by various methods. The methods covered include injections with water, lime, lime/ fly ash and potassium chloride and mixing soil with lime, fly ash, lime-cement and Portland cement admixtures. Other methods considered are asphalt stabilization and soil encapsulation. These methods modify expansive soils and unstable rock materials in order to improve performance for slope stability, bearing capacity, road pavements, and excavations in restricted spaces, and to reduce differential settlements. A wide selection of processes and materials are available for the engineer and the course describes suitability for given site conditions. Other measures, which protect expansive soils from wide swings in moisture or water movement, such as geotextiles, geomembranes, slurry walls, and surface water and ground water control, are not covered in this course.

If the existing subgrade has poor strength or instability due to excess clay, expansive clays, or other problems such as high watertables, ground improvements will protect from potential settlement and provide the required bearing capacity. Other soils which contain clays such as bentonite or montmorillonite can expand and increase in volume when exposed to water. Expansive soils can shrink or decrease in volume when water is not present.

Unstable soils in the United States, which includes expansive clay soils cause billions of dollars of damage to property each year and may exceed the total costs of natural disasters. Expansive soils are a problem in over 30 states especially in Texas, Colorado, Virginia, North Dakota, Oklahoma and Montana. Expansive clay soils are affected by the shrink/swell cycles caused by changes in moisture content during the year. The amount of swell depends on the amount of clay, relative density, location of water table and overburden stress. Affected sites include building foundations, roads and highways, parking lots, building pads, driveways, houses, pools and decks. Damage may range from sticking doors and cracked walls to foundation failures and building condemnations.

This course includes a multiple-choice quiz at the end, which is designed to enhance the understanding of the course materials.

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NY PE & PLS: You must choose courses that are technical in nature or related to matters of laws and ethics contributing to the health and welfare of the public. NY Board does not accept courses related to office management, risk management, leadership, marketing, accounting, financial planning, real estate, and basic CAD. Specific course topics that are on the borderline and are not acceptable by the NY Board have been noted under the course description on our website.