Experimental study on fatigue properties and fracture characteristics of sandstone under different cycle times and frequencies conditions

Abstract

Many underground engineering activities (e.g., drilling, tunnel excavation, vehicle loading, hydraulic fracturing, compressed air energy storage) generate dynamic disturbances, producing seismic waves or periodic cyclic loads, causing instability and failure of underground rock masses under the influence of fatigue loading. This paper focuses on the mechanical behavior of sandstone specimens under fatigue loading. Triaxial fatigue mechanical tests under multi-stage incremental cyclic loading were conducted under different cycle numbers, loading frequencies, and frequency sequences. The influence of the aforementioned factors on the strength and deformation characteristics, energy evolution, and macroscopic failure modes of sandstone specimens were systematically analyzed, revealing the fatigue meso-microscopic failure characteristics of sandstone under multi-stage incremental cyclic loading. The research results show that: as the number of cycles in the fatigue loading stage increases, the strength of sandstone specimens exhibits a three-stage change of “decrease-stabilize-decrease”, with both crack size and number increasing, and intergranular cracks being dominant at the specimen failure fracture surface. As the loading frequency increases, the fatigue life and internal strain energy of sandstone increase, the volume and complexity of internal cracks increase, and the proportion of transgranular cracks at the fracture surface increases. The loading frequency sequence has no significant effect on specimen strength and energy evolution. Under sequential frequency conditions, sandstone exhibits higher crack volume and a more complex crack system, with an increase in the scale of intergranular cracks at the fracture surface.