Abstract: the evolution of the critical state of TDA-graded aggregates is essential to safety for TDA application in railway roadbed, but the investigations on effects of TDA on the critical state are rare. This paper presents an experimental investigation on the stress strain relationship of TDA-graded aggregates through large scale triaxial apparatus by consolidation and drainage conditions. In total, 12 groups of specimens were carried out considering four volumetric TDA content and three confining pressures. The experimental results show that the shear properties of the TDA sub-ballast mixture are characterized as strain-softening when the TDA volume content is less than 20%, and show strain hardening when the TDA volume content is greater than 20%. And the critical state line (CSL) in space, and relationship between the TDA content and the values of parameters of CSL is linearity. In consequence, the strain-stress of TDA-graded aggregates based on the critical state line characteristics was predicted, and compared to the corresponding measured values with good agreement. It highlights the feasibility of the new formula for the TDA-graded aggregates. These experimental findings are helpful for modeling aggregates with TDA inclusion.

Key words: tire derived aggregate(TDA), graded aggregate, railway ballast, critical state, large-scale triaxial test