Long-term strength and deformation size effect of gangue cemented backfill in acid mine water

Abstract

The mine water environment can seriously affect the long-term strength and deformation of the backfill body, thereby affecting the stability of the goaf. In this study, the gangue cemented backfill (GCB) of different sizes were placed in different environments (air, water, single H2SO4 solution, and H2SO4 solution coupled with load), the deformation and ultrasonic pulse velocity (UPV) of specimens were recorded with age. The compressive strength, acoustic emission (AE), and resistivity of GCB during the uniaxial compression at 360 days were monitored. In addition, the microscopic morphology of GCB was observed by scanning electron microscopy (SEM), and the damage model of GCB in the process of uniaxial compression was established. The research showed that: the deformation of GCB was fast in the first 90 days and gradually slowed down. The bigger the size was, the greater the instantaneous creep of the GCB was, and the faster the increase rate of the initial deformation was. The UPV of eroded GCB experienced three stages of growth-stability-decrease. The UPV of the smaller GCB increased rapidly in the early stage and decreased rapidly in the later stage. At 360 days, the order of compressive strength of GCB in different media is: water > air > single H2SO4 solution > H2SO4 solution coupled with load, and the compressive strength decreases with the increase of specimen size. In the process of uniaxial compression, the larger the size of the GCB, the larger the number of AE rings detected. The smaller the size of GCB, the stronger the AE characteristics appeared in the initial compaction stage. During the loading process, the resistivity curve of GCB changed approximately in a “U” shape. The smaller the size of GCB, the slower the increasing rate of resistivity in the post-peak failure stage. The abrupt change in the AE ring and the stable resistivity stage could be used to predict the failure of the GCB. The research could provide a reference for the design of the erosion resistance of GCB.