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• The mechanical response of stress-damaged CTB (SDCTB) was investigated. • The effect of stress damage level on the mesoscopic structure of SDCTB was determined. • The rupture process of SDCTB was probed based on AE signaling and fractal theory. • Compaction enhancement and cracking damage together determine SDCTB performance. The mechanical response of cemented tailings backfill (CTB) is essential for its achievement of underground mine ground pressure management and productivity improvement. However, long-term, continuous, high-intensity mining causes CTB subject to mining stress disturbance, which inevitably affects its mechanical properties and stability when serving as a load-bearing structure. Therefore, the stress-damaged CTBs (SDCTB) were prepared to take 20%, 40%, 60%, and 80% uniaxial compressive strength (UCS) as the stress-disturbed levels (SDL) in this study. The effects of SDLs and curing ages (3, 7, 14, and 28d) on the mechanical properties and damage characteristics of STCTB were also investigated. The results showed that as SDL enhanced, the UCS and elastic modulus of the backfill (except SDCTB with 60%–80% SDL) increased and then decreased, and 20% SDL was the turning point. Meanwhile, the external load disturbance significantly affected the initial compaction stage of the stress–strain curve of the backfill. Proper SDL reduced the porosity of SDCTB and induced the transformation of macropores to mesopores and micropore. In addition, the AE signals of CTB and SDCTB with 20% SDL showed an active-calm-active stage during compression. The AE signals of SDCTB with 40%–80% SDL remained active stage. The higher SDL aggravated the crack sprouting and expansion rate of the backfill. Also, the correlation dimension (D) of AE ringing counts and amplitudes fully reflected the rupture characteristics of the backfill. The failure mode of SDCTB changed from mixed tensile-shear to tensile failure as the curing age increased. Comprehensive macro-mesoscopic experimental outcomes, the effect of compaction enhancement and cracking damage of the backfill under the external load were proposed, and the two were competing. The results of this study provide a theoretical basis for the stability assessment of the backfill under mining stress disturbance. [ABSTRACT FROM AUTHOR]

Frequent mining stress disturbances in deep-earth resource extraction lead to different degrees of initial damage within cemented tailings backfill (CTB), which in turn changes the structural characteristics of the matrix and significantly affects the stability of CTB. To simulate the stress disturbance process of CTB during mining activities more realistically, cyclic loading and unloading disturbances were performed on the CTB. The stress disturbance levels (SDL) were 20, 40, 60, and 80% uniaxial compressive strength (UCS), and the stress disturbance counts (SDC) were 5, 10, 15, and 20 times, respectively. Subsequently, a series of experimental studies were conducted on CTB and disturbed damage CTB (DCTB) using UCS, nuclear magnetic resonance, ultrasonic pulse velocity (UPV) testing, and acoustic emission (AE) monitoring. The results show that the UCS of the backfill decreased with increasing SDL and SDC, except for 20% SDL and 5th SDC. The elastic modulus exhibited a rise at 20%–40% SDL and a fall at 60%–80% SDL. Compared with CTB, the stress–strain curve of DCTB showed a left shift - overlap - right shift - accelerated right shift change in the compacting stage with increasing SDL. Moreover, the porosity and UPV reflected by the mesoscopic structure correspond to the trend of UCS. The correlation mechanism between mesoscopic structure and macroscopic strength was determined, and the initial damage degree of DCTB was defined in terms of the average variation characteristics of macro-mesoscopic parameters. According to the AE monitoring results, it was observed that increasing SDL and SDC led to a significant increase in the AE energy active stage during loading. The damage curve established from the AE energy considering the initial damage degree rose exponentially. As the initial damage degree intensified, a noticeable and wide-range drop in the b -value before the peak was observed, indicating the occurrence of frequent large-scale fracture activities within the DCTB. Also, the damage degree of DCTB intensified, the collapse zone increased, and the failure mode of the backfill transformed from tensile to mixed tensile-shear damage. The research results can provide theoretical support and a reference basis for the stability analysis and strength design of the backfill under the action of mining stress. [ABSTRACT FROM AUTHOR]

• The effect of PF and LR on the mechanical characteristics of PFCPB was analyzed. • The relationship between energy evolution and crack extension was determined. • Cracks in PFCPB tended to sprout in the stress concentration at the PF tip. • The energy development trend of PFCBP and CPB corresponded to the AE signal. Loading rate (LR) and initial defects are the vital factors influencing the mechanical properties of cemented paste backfill (CPB). Under the action of external load, the essence of the deformation and damage of the filling body is the evolutionary process of progressive damage driven by energy, which is the comprehensive performance of crack closure, development, expansion, and convergence. In this paper, uniaxial compressive strength (UCS) tests with different levels of LRs were conducted on 0°, 45°, 90° prefabricated fracture CPBs (PFCPB), and CPB. The results show that UCS and elastic modulus of the filling body were positively correlated with LR. The mechanical properties of the filling body were degraded by PF. During loading, the top and bottom surfaces of 0° and 45° PFs were closed, and the stress–strain curves showed stress drop phenomenon. The stress drop of the curve corresponded to the rapid release of elastic energy and the rapid increase of dissipated energy. The dissipation energy curve corresponded to crack opening and expansion, which could be divided into slowly growing, steadily growing, and rapidly growing stages. The steadily growing stage of the dissipative energy curve for higher LRs was beneath the other curves, and a decelerating rising period occurred in the rapidly growing stage. Meanwhile, the dissipation energy curves of 0° and 45° PFCPBs suffered from an accelerated rise, slow rise, and rapid rise periods in the rapidly growing stage. The cracks after the failure of PFCPB mainly included resistance to tensile cracks, wing cracks, coplanar and non-coplanar secondary cracks. The failure mode of PFCPB was the occurrence of mixed shear-tension failure, and CPB exhibited shear failure. The progressive damage law and cracking mechanism of the filled body were investigated with the help of AE energy rate (cumulative AE energy)-energy-time (strain) curves and microscopic morphology. The results could provide a theoretical basis for the stability assessment of the filling body. [ABSTRACT FROM AUTHOR]