Critical Assessment of Current Standards for Wetting Deformation of Rockfill Materials Using the Discrete-Element Method

To study whether the triaxial specimen size suggested by the GB/T 50123-2019 and ASTM D7181-20 meets the representative element volume (REV) for the wetting deformation of rockfill materials, the effect of specimens with different ratios (Rd) of specimen diameter to the largest particle size on the wetting deformation of the basalt rockfill materials was analyzed by the discrete-element method (DEM). First, a wet deformation simulation method for rockfill materials was developed according to the wet deformation mechanism. The particle crushing simulation method, considering the strength dispersion and size effect, was introduced. Then, the DEM model parameters were determined by matching with the laboratory test, and the validity of the wetting simulation method was verified. Finally, triaxial wetting simulation tests under different conditions were conducted, and the reliability of wetting deformation obtained using specimen sizes suggested by the standard was analyzed. The results show that the wetting procedure of the rockfill materials can be reproduced by linearly transforming the DEM model parameters from the dry state to the saturated state. The wetting strains and their variation coefficients obtained using two specimen sizes with Rd = 5 and 6 have basically the same variation laws with confining pressures and wetting stress levels, but the values are different. When the criterion of variation coefficient is 5%, the triaxial specimen size (Rd = 6) of 360 mm in diameter and 720 mm in height can be adopted as the REV for the wetting axial strain and wetting volumetric strain, whereas the specimen size (Rd = 5) of 300 mm in diameter and 600 mm in height does not satisfy the requirement in the case of high wetting stress levels and high confining pressures. It is suggested that the diameter of the specimen adopted in the triaxial wetting test of rockfill materials not be less than six times the largest particle size.