Under the periodic rise and fall of reservoir water levels, the deterioration of fractured rock masses in the bank slope drawdown zone becomes significant, posing a serious threat to the stability of reservoir bank slopes. Taking fractured sandstone from the drawdown zone of the Three Gorges Reservoir area as the research object, periodic water-rock interaction tests were conducted to analyze the macroscopic mechanical properties and the evolution of microscopic porosity of the fractured sandstone. The results show that under periodic water-rock interaction: the uniaxial compressive strength and elastic modulus of the fractured sandstone exhibit a staged deterioration characteristic of “rapid in the early stage and gradual in the later stage”. The deterioration degree is relatively large during the first two water-rock cycles, and gradually decreases and tends to stabilize after four cycles. Significant differences exist in the deterioration degree of mechanical properties for fractured sandstones with different inclination angles; the largest deterioration occurs at an inclination angle of 30°, and both the deterioration magnitude and the differences among various fracture inclinations gradually decrease with increasing cycles. The crack initiation mode of the fractured sandstone with the same inclination angle remains unchanged, while the failure mode varies: at 0° and 90°, it gradually changes from tensile failure to tensile-shear composite failure; at 30°, 45°, and 60°, the degree of tensile-shear composite failure intensifies. The cumulative increase of internal pores and the weakening of cementation within sandstone are the fundamental reasons for the cumulative deterioration of its mechanical properties and the change in failure modes. The research results can provide a theoretical basis for the stability analysis and long-term safety evaluation of reservoir bank slopes in the drawdown zone.
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