Volume 33, Issue 1 (January 2010)
Matric Suction Measurement in Stress Path Cyclic Triaxial Testing of Unbound Granular Base Materials
Unbound granular base (UGB) materials are commonly placed as part of pavement foundations. These materials are generally designed to be in an unsaturated state in order to resist the dominantly cyclic loading. Therefore, the response of UGB materials under cyclic loading needs to be studied using the framework of unsaturated soil mechanics. This requires the measurement of matric suction evolution during cyclic loading, which is a major experimental challenge to be resolved. This paper presents the development of a cyclic triaxial testing system and associated experimental techniques that meet the challenges of testing UGB materials as unsaturated soils. The testing system enables the initializing of matric suction of a specimen and facilitates direct measurement of its evolution during cyclic loading. Two types of cyclic loading could be imposed: with constant cell pressure and with cyclic cell pressure. Selected test results of both types of cyclic loading were presented to demonstrate satisfactory performance of the proposed methodology. Furthermore, a detailed analysis of these selected test results was also undertaken to show the importance of matric suction for understanding the behavior of UGB materials under cyclic loading.