INFLUENCE OF LATERAL RESTRAINT ON THE SWELLING BEHAVIOR OF EXPANSIVE SOILS

Most of the methods available for prediction of the amount of heave of expansive soils are based on test results obtained under fully lateral restraint conditions in the oedometer. However, in the field heave is not a one-dimensional volume change but more likely a three-dimensional process. Consequently, surface heave predicted from results of oedometer tests is usually conservative and largely differs from heave actually observed in the field. This paper presents the procedure and results of a laboratory testing program in which the vertical and the volumetric swells of compacted expansive soil samples were concurrently measured using a hydraulic triaxial stress path apparatus. Series of triaxial swell tests were conducted and the results were compared with the volume change measured in samples tested under one-dimensional loading conditions in the oedometer. The ratio of triaxial ultimate vertical swell to that obtained from oedometer, TOR, varied between about one third and two third and found to increase with applied load and decrease with increasing initial water content and dry unit weight. For samples subjected to triaxial state of stresses, the ratio of swell in the vertical direction to the volumetric swell, SR, was evaluated. The value of SR at ultimate swell ranged between 0.40 and 0.78, and the overall average value for all tests at all time intervals was about 0.57. The test results also indicated that the value of SR increased with increasing applied confining pressure, and for a particular test it changed with elapsed swelling time. (A)