Experimental Investigation on the Deformability, Ultrasonic Wave Propagation, and Acoustic Emission of Rock Salt Under Triaxial Compression

Abstract

Ultrasonic waves, which constitute an active testing method, and acoustic emissions (AE), which can be applied as passive testing technology, can reveal rock damage processes in different ways. However, few studies so far have simultaneously adopted both, owing to the limitations of the experimental apparatus. However, the simultaneous use of both methods can improve the experimental efficiency and help to understand the rock damage evolution more comprehensively. In this study, concurrent experiments of ultrasonic waves and AE activities were carried out on rock salt under uniaxial compression, and the deformation characteristics were measured. The fracture process was divided into four stages with individual characteristics: the elastic compression stage, brittle-ductile transition with crack initiation, brittle-ductile transition with damage initiation, and plastic deformation and strain hardening stage. The ultrasonic wave velocity, crack density, ultrasonic wave amplitude, and attenuation coefficient were obtained to evaluate the damage process. The ultrasonic wave amplitude and the attenuation coefficient were recommended as forecast indicators, owing to their sensitivity and operability of measurement. The confining pressure had an inhibitory effect on crack expansion and on the AE activity, and the damage ultimate stress was defined and determined according to the AE activity and energy release characteristics. Four critical strengths of the crack initiation threshold stress, dilatancy boundary stress, short-term strength, and damage ultimate stress of rock salt were determined and then discussed. These results are valuable in evaluating rock damage and guiding the operation of underground salt caverns. Appl. Sci. 2019, 9, 635 2 of 15 computed tomography (CT), and density or infrared radiation detection. However, they are not widely used, owing to the strict requirements on testing conditions or equipment. In recent years, an active method, as represented by ultrasonic wave detection, and a passive method, as represented by acoustic emission (AE) monitoring, have been accepted by many scholars, and they have become essential tools in analyzing and predicting rock damage.Ultrasonic waves are a good index for evaluating the change of internal structure and mechanical properties of rocks. When the elastic wave encounters certain obstacles during propagation, such as inclusions, holes, and cracks, ultrasonic attenuation will occur. This process is presented by the decline of ultrasonic wave velocity or amplitude [9]. In the 1970s, Oconnell and Budiansky [10,11] studied the differences of the elastic modulus in crack-bearing rocks and crack-free rocks, and obtained a relationship between ultrasonic wave velocity and the elastic modulus of rock mass. An equation depicting ultrasonic wave velocity and fracture density was established. However, it was not widely used, owing to the difficulty of P-wave (Primary wave) and S-wave (Shear wave) velocity measurement at that time. In the 1990s, Bellang et al. [12] ev...

Mechanical and Acoustic Emission Characteristics of Sandstone through Triaxial Unloading Test after Cyclic Freezing‐Thawing Treatment

“…For each freezing-thawing cycle, we also observed all the accumulated AE energy of samples had a maximum increasing rate when the counting rate reached the maximum with the formation of through shear crack. is result is consistent with that in other studies such as Li et al [21], who found that the accumulated energy released quickly when rock sample approached to its failure state. e increasing rate of AE energy may be potentially used as an index to identify the big rock fracture.…”

“…us, the freezing-thawing treatment had a minor influence on the stress-strain behaviors when the confining pressure was still high. is inhibitory effect of confining pressure on crack expansion was also reported by other researchers such as Li et al [21] and Wu et al [33]. e latter research experimentally showed the microcracks partially closed under confining pressure using fluorescence microscopy, but the total porosity was not significantly affected.…”

“…is acoustic emission (AE) is a phenomenon that occurs when strain energy is released in the form of elastic waves during the failure process of material [19]. An AE device can thus be utilized to monitor the damage and cracking of rock materials [20,21]. Given the low cost, easy, and efficient advantages compared to other in situ stress test methods, the AE technique has been broadly applied to test the rock mechanics under true-triaxial conditions by analyzing the AE characteristics for the understanding of mechanical properties in the process of rock failure [1,14,[22][23][24].…”

Construction of mathematical models of the stressed-strained state of a material with a porous water-saturated base under dynamic load

“…Paper [8] reports an experimental study of the deformability of media during the propagation of ultrasonic waves and acoustic emission of rock salt at triaxial compression. The study does not consider the propagation of waves in deformable media and their interaction under dynamic mobile loads.…”

Acoustic‐Mechanical Responses of Intact and Flaw‐Contained Rock Deformation under Uniaxial Compression: A Comparison

“…Isah et al [7] introduced a new multichannel fiber Bragg grating sensors (MC-FBGs) to investigate deformation properties of intact rock samples. Li et al [8] studied the deformation and cracking characteristics of rock salt under triaxial compression by ultrasonic waves and AE techniques.…”