Cubical Pneumatic Cushion Triaxial Soil Test Unit

A cubical triaxial unit (CTU) was designed and built that used pneumatically pressurized flexible cushions to apply a three-dimensional, independently controlled, compressive stress state to a cubical soil sample measuring 50.8 mm along each side. The apparatus was computer controlled and could operate safely up to pressure levels of 1 MPa. The performance of the CTU was evaluated by comparing it to data obtained from an existing cylindrical triaxial device. Also, data from the CTU were used to validate Bailey and Johnson’s (1989) soil compaction model. The CTU will be used to determine how soils react to three independent principal stresses, and to aid in the development of finite element techniques to predict soil and soil-machine behavior.