Experimental study on progressive damage of dolomite under cyclic loading

Abstract

[Objective] To study the damage development and failure mechanism of the bedrock of pumped storage power station in karst area under cyclic loading, [Methods] the incremental cyclic loading-unloading test and cyclic loading-unloading test with large stress amplitude are carried out on the typical dolomite rock.[Results] The result show that:(1) For the incremental cyclic loading-unloading tesy, pore compaction dominates under low stress cycles [(0.15~0.35)σ_ucs,(0.35~0.55)σ_ucs], and irreversible strain appears under high stress [(0.75~0.95)σ_ucs], indicating damage accumulates with loading and the elastic modulus decreases while the Poisson's ratio increases with cyclic loading.(2) When the stress exceeds the ‘fatigue stress threshold' [(0.85~0.90)σ_ucs], the acoustic emission signal generates continuously during the cyclic loading and unloading process, and the damage accumulates until the rock failure.(3) For the cyclic loading-unloading test with large stress amplitude, for the test with the stress range of(0.30~0.85)σ_ucs, the sample is not damaged. For the test with the stress range of(0.30~0.90) σ_ucs, the damage process could be divided into three parts: the initial compaction stage, the stable damage accumulation stage, the damage accelerated accumulation stage. For the test with the stress range of(0.30~0.95)σ_ucs, the damage of rock sample is rapidly accumulating to failure.[Conclusion] The energy evolution law and mechanical property degradation mechanism of dolomite during loading and unloading were studied, which could provide support for the design and engineering monitoring of pumped storage reservoirs.

Keywords

cyclic loading and unloading / acoustic emission / fatigue damage characteristics / b value / damage variable / influencing factors / mechanical properties