The co-placement of mine tailings and fly ash (CMF) can reduce acid mine drainage (AMD) production and decrease metal mobilization. This aids in waste management construction. However, few people have studied a large number of tailing sand-fly ash mixtures under the condition of neutral saturated solution in tailing ponds, wherein the pozzolanic reaction is highly gradual. In this study, a series of tests were conducted to determine the monotonic and cyclic shear characteristics of a mixture of fly ash and tailings. In particular, the effects of the fly ash content on the monotonic shear peak, shear strength parameters, dynamic modulus, and damping ratio of the mixture were analyzed. The results reveal that in a monotonic shear test, the peak shear strength of the saturated CMF mixture decreases as the fly ash content increases. The shear strength parameters (cohesion c and internal friction angle φ) were observed to increase and decrease linearly, respectively, as the fly ash content increased. Furthermore, the maximum dynamic shear modulus was observed to decrease by 41.4% as the fly ash content increased from 0 to 50%, during the cyclic cutting process. Moreover, the experimental results fit well with the fitting formula for the variation in shear modulus in the cyclic shear process of the saturated CMF mixture with varying fly ash content. Meanwhile, the initial damping ratio of the cyclic shear was observed to increase from 10.3 to 13.6% as the fly ash content increased. Therefore, when the CMF method is used to treat AMD waste, it is necessary to consider the extent to which the design stability of the tailing pond may be reduced. These experimental results can be used as a reference for similar CMF projects.
Keywords: CMF mixture; Damping ratio; Dynamic shear modulus; Fly ash; Shear strength.