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|Title:||Predicting potential heave and heave with time in swelling foundation soils|
|Authors:||Soils and Pavements Laboratory (U.S.)|
Johnson, Lawrence D.
|Publisher:||Geotechnical Laboratory (U.S.)|
Engineer Research and Development Center (U.S.)
Abstract: This study evaluates procedures for predicting one-dimensional potential heave of foundation soils and the rate at which heave may occur. A computer program ULTRAT (Ultimate and rate of heave) was developed for predictions of potential heave and heave with time based on two models for characterization of swell behavior: the soil suction and mechanical swell models. The soil suction model relates volume change with change in matrix soil suction and water content. Time rate of heave may be predicted from numerical solutions of a simplified advanced diffusion flow equation. The mechanical swell model uses results from swell tests performed in the consolidometer. Laboratory tests were performed to provide data for characterization of swell behavior using the models in the program ULTRAT. Testing procedures for the soil suction model are simple, economical, and expedient. The data are also useful for soils with any degree of saturation and the effect of lateral pressures may be accounted for in analyses. Testing procedures for the mechanical swell model using consolidometers are time consuming. Therefore, relatively few tests are usually performed which may not provide adequate representation of field soil conditions. The data are useful only for soils with a final degree of saturation equal to 100 percent and lateral pressures are not accounted for in analyses. Swell tests must be performed for each initial water content encountered in the field, whereas suction tests need be performed only to evaluate the suction-water content relationship for the required range of water contents. A parametric study led to the development of simple, empirical equations for predicting potential heave and heave with time of slab foundations on homogeneous swelling soils above a stable water table or above nonswelling soil. Field measurements taken from test sites were compared with predictions of potential heave using eight published empirical methods, the empirical equations developed as part of this study, and the program ULTRAT. Preliminary analyses of heave with time using the empirical equations were also compared with field observations. The results indicate that several methods provided useful predictions of potential heave of the field test sections. These methods include the empirical equations developed as part of this study and use of ULTRAT. The soil suction model provided upper and lower limits of heave at the field test sections if all or 1/3 of the volumetric swell, respectively, is assumed to occur as heave in the vertical direction. Heave with time predictions are burdened with the problem of determining effective field coefficients of permeability or swell. Effective coefficients of permeability or swell are a function of the availability of water as well as a measure of the field permeability. Maximum upper limits of 0. 0001 ft/day and 0.02 ft²/day for the effective coefficients of permeability and swell, respectively, were determined for the soils beneath the field test sections.
|Rights:||Approved for public release; distribution is unlimited.|
|Appears in Collections:||Technical Report|
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