Geomechanical behaviour of fibre-reinforced cemented paste backfill under cyclic loading conditions

Abstract

Cemented paste backfill (CPB) is considering a promising mine backfilling technology with several technical, environmental, and economic benefits for the underground mining operation. After placed into underground voids (termed stopes), the hardened CPB mass is required to provide reliable ground support to control ground pressure and limit surface subsidence. However, due to the complex field loading conditions, CPB mass may experience dynamic loadings induced by mining activities (such as drilling, blasting, and mechanical excavation) and seismic events. However, as a soft cementitious material, aged CPB is highly brittle in nature and

also featured with poor strain-hardening capabilities, the low tensile strength, and weak post- peak resistance. As a result, the in-situ CPB mass may undergo catastrophic failure under

complex field dynamic loading condition. This highlights the complexity of loading conditions in-situ and the need to improve the mechanical stability and performance of CPB. Consequently, fiber reinforcement has recently attracted increasing attention in the improvement of the geomechanical behavior and performance of CPB. The benefits of small fiber inclusions on the mechanical performance of cementitious composites under quasi-static loading conditions and fiber reinforced cementitious composites (FRCCs) under cyclic loading conditions have been fairly established by previous researchers. However, there are no studies that have systematically studied the application of fiber reinforcement in CPB technology under cyclic loading conditions. The purpose of this thesis research is to study the geomechanical behavior of fiber- reinforced cemented paste backfill (FR-CPB) under cyclic loading conditions. This body of work

studies the effects of fiber inclusion on the evolutive cyclic compressive and tensile behaviors and mechanical properties of FR-CPB. Curing time, fiber length and fiber content were used to study the evolution of FR-CPB’s mechanical properties, including hysteretic energy dissipation, secant modulus, degraded stress, and damping index. Cyclic stress-strain data reveals that the geomechanical behavior of FR-CPB is highly influenced by curing time. Aging of FR-CPB results in a strengthened fiber-bridging effect leading to improvement in composite strength and, thus, load carrying capacity through full realization of the cement hydration process. [...]