1. ERDC Knowledge Core
2. Pre - Engineer Research and Development Center (ERDC)
3. Geotechnical Laboratory - (4/16/1978 - 2/22/2001)
4. Publication
5. Miscellaneous Paper

Title:	Measurement of horizontal and vertical swell pressures from a triaxial laboratory test ; a feasibility study
Authors:	United States. Assistant Secretary of the Army (R & D) Johnson, Lawrence D.
Keywords:	Swelling soils Soil mechanics Skin friction Foundations Soils testing
Publisher:	Geotechnical Laboratory (U.S.) Engineer Research and Development Center (U.S.)
Series/Report no.:	Miscellaneous paper (U.S. Army Engineer Waterways Experiment Station) ; GL-87-23.
Description:	Miscellaneous Paper Abstract: Horizontal and vertical swell pressures in cohesive soil influence the performance of permanent military facilities found on such soils. Horizontal pressures influence skin friction on deep foundations that may lead to uplift and heave of foundations in expansive soil or downdrag and settlement in consolidating or collapsible soil. Excessive horizontal pressures on basement and retaining walls may require uneconomical structural designs. Vertical swell pressures in foundation soils often lead to foundation heave and may cause structural distress. The purpose of this study was to determine the feasibility of evaluating vertical and horizontal swell pressures using a triaxial test apparatus. This work developed a double chamber triaxial apparatus and test procedure to measure vertical and horizontal swell pressures caused by introducing water to a 1.4-in. diam by 3.5-in. high soil specimen subject to no volume change. This equipment and test procedure eliminate lateral skin friction normally present during one-dimensional consolidation testing and should provide improved results compared with tests performed in a one-dimensional consolidometer. The specimen may subsequently be consolidated and rebounded without lateral skin friction to evaluate consolidation parameters. The shear strength may also be determined on the same specimen following measurement of the swell pressures or consolidation parameters. Lateral confining pressure on the specimen is currently limited to 80 psi to accomplish the purpose of this study, but the pressure may be increased up to 200 psi after further calibration tests. Applied horizontal pressures cannot exceed vertical applied pressures; this apparatus will measure lateral expansion if horizontal swell pressures exceed the horizontal applied pressure. Results of three series of tests performed on two different expansive soils trimmed from undisturbed boring samples indicated no difference in swell pressure between vertical and horizontal orientations of the specimen. Optical analysis of two thin sections of intact soil prepared from one of the soil samples indicated birefringence or anisotropy. Consolidation and strength parameters determined using the double chamber triaxial apparatus are also consistent with those performed on similar specimens using other test apparatus. An exception is that the elastic modulus evaluated for soil specimens tested in the double triaxial chamber provides an upper bound limit up to two times (four times for soft soils) of that evaluated from standard triaxial tests. This is attributed partly to friction from an O-ring required to pass the vertical loading ram through the outer chamber into the inner chamber and use of a solid piece of geotextile filter fabric to promote flow of water in and out of the specimen. Additional work should be performed to expand the lateral range of confining pressures that may be applied by the apparatus. A variety of filter fabrics should be tested to further reduce the calibration correction and improve evaluation of the elastic modulus. A variety of undisturbed clays and clay shales should be tested to confirm the observation that swell pressures are isotropic under no volume conditions. This study has shown that measurement of vertical and horizontal swell pressures prior to consolidation or strength tests is feasible.
Rights:	Approved for public release; distribution is unlimited.
URI:	http://hdl.handle.net/11681/10229
Appears in Collections:	Miscellaneous Paper