Study of mechanical behavior and cracking mechanism of prefabricated fracture cemented paste backfill under different loading rates from the perspective of energy evolution

Abstract

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.