Stress Memory in Acoustic Emission of Rock Salt Samples in Cyclic Loading under Variable Temperature Effects
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Stress Memory in Acoustic Emission of Rock Salt Samples in Cyclic Loading under Variable Temperature Effects V. L. Shkuratnika*, O. S. Kravchenkoa, and Yu. L. Filimonovb** a
National University of Science and Technology—MISIS, Moscow, 119049 Russia *e-mail: [email protected] b Gazprom geotekhnologii, Moscow, 123290 Russia **e-mail: [email protected] Received March 10, 2020 Revised March 12, 2020 Accepted April 10, 2020
Abstract—The behavior of acoustic emission in uniaxial cyclic loading of rock salt samples from the Kaliningrad deposit is determined. The samples were tested under varied temperatures and ratios of maximal stresses in sequential loading cycles. The experimental curves of acoustic emission activity and maximal stress and temperature of the previous cycle are obtained. Stress memory in acoustic emission manifests itself equally stably under constant higher and lower temperatures. Memory of the maximal stress of the previous cycle persists under higher temperature in the next cycle and vanishes under lower temperature in the next cycle. In case of the same maximal stresses and constant or higher temperatures in the successive cycles, the stress memory effect is vague: the stress estimated on this base is lower than the maximal stress of the previous cycle. Keywords: Rock salt, stress–strain behavior, measurements, control, acoustic emission, cyclic loading, stress memory in acoustic emission. DOI: 10.1134/S1062739120026662
INTRODUCTION
Safe and efficient mining of rock salt, as well as construction and operation of underground hydrocarbon storages in saline deposits requires rheological estimates and stress–strain analysis data on enclosing rock mass [1–5]. To this effect, the geocontrol techniques used in recent years are based on specific ability of rocks to preserve and reproduce under certain treatment the information on the maximal stresses experienced earlier. Such phenomena are commonly called as memory effects, including the best studied stress memory effect in acoustic emission (Kaiser effect) [6–9]. This effect appears in cyclic loading of a geomaterial, with cycle-to-cycle increase in the maximal stress σ max , and comes out as a jump in the acoustic emission activity N Σ in a cycle n so that σ max( n ) exceeds
σ max( n −1) in cycle (n − 1) . The stress memory effect develops stronger when the modes of the test and initial loading of a sample coincide the most accurately [10, 11]. It is proved that in salt rock, the stress memory effects are governed by high plasticity and pronounced rheology. These properties are susceptible to temperature conditions [12–16]. Down to recent times, the influence of the thermal factor on the stress memory effect in acoust
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