Influence of suction on heave of expansive soils
Johnson, Lawrence D.
Miscellaneous PaperAbstract: Certain types of foundation soils will swell from sorption of moisture, often causing differential heave and severe damage to overlying structures. A measure of the force causing these expansive soils to imbibe moisture is given by the magnitude of the negative pore water pressure (or suction) in the pore water of the soil. Estimations of heave and rates of heave in foundation soils can be made with suction data; however, information on the influence of suction has been limited. This investigation was conducted to determine the influence of suction pressures on heave in some expansive soils beneath structures. An important part of the project was the development and operation of a pressure membrane apparatus capable of simulating and measuring the in situ matrix suction of expansive clay soils. The relationship of suction to soil properties was reviewed, and some effects of field conditions on heave were examined. Selected expansive soils were tested under applied pressures simulating the in situ vertical loads. Specimens were obtained from sites located at Jackson, Mississippi, and Lackland Air Force Base, Texas. The test results were used to develop relationships between suction and water content and to determine the degree of saturation, the void ratio, and the coefficient of permeability. Test results showed that a minimum of 0.07 and 0.23 ft of heave will occur beneath lightly loaded structures of about 1 psi at the Jackson and Lackland sites, respectively, due to changes in matrix suction pressures. These estimates exclude swell based on changes in matrix suction beyond the 48 hours allowed for each incremental pressure change during the pressure membrane tests and additional swell that could result from cyclic wetting and drying.
Soils and Pavements Laboratory (U.S.)Engineer Research and Development Center (U.S.)
Expansive soils; Heaving; Soil mechanics; Swelling soils; Hydrostatic pressure; Foundations
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