UPGRADING EQUIPMENT AND PROCEDURES FOR STRESS PATH TRIAXIAL TESTING OF COARSE-GRAINED MATERIALS

Advanced laboratory testing is often the only way to gain an insight i nto the mechanical behavior of soils in the whole range from small str ains to failure, which in some cases is required for the engineering m odeling of complex structures. When such structures are rockfill darns , the use of a large apparatus in-laboratory is virtually unavoidable because of particle size, even though testing becomes far more difficu lt than usual. This paper presents problems arising from the upgrading of an existing large triaxial cell in order to provide fully automate d stress-path control. Because of the large dimensions of the apparatu s, implementation of both stress rate and strain rate controls posed a number of unusual problems. Even though the control had to be careful ly tuned in order to consider strain-softening behavior, the adopted p rocedure proved successful. The new cell produced good results for dif ferent kinds of stress paths, with satisfactory control in all stages.