ABSTRACT:

Gas storage caverns built within rock salt formations experience cyclic loading conditions either when gas is injected into the storage or when the gas is retrieved. The behavior of polycrystalline rock salt under cyclic loading conditions is well documented in the literature; however, single-crystal rock salt's behavior under cyclic loading is yet under-explored. This paper attempts to address this gap using cyclic and quasi-static loading-unloading tests on natural single-crystal specimens. Additionally, single-crystal rock salt's mechanical response is rather anisotropic; therefore, specimens with various crystal orientations are tested and evaluated. The specimens investigated in cyclic tests at 70%–80% of their unconfined compressive strength did not exhibit a significant change in their Young's modulus and damage parameters even after 30 cycles. However, the specimen tested on 30° to (1 0 0) in (0 1 0) direction showed a consistent increase in damage parameter with the number of cycles showing this crystal orientation is prone to fatigue damage.

1. Introduction

Rock salt is one of the prospective rock masses suitable for storing hazardous waste or various forms of energy (Hansen and Leigh, 2011; Marques et al., 2013; Titler et al., 2011; Urai et al., 1986). Rock salt can adapt to variation in the storage conditions such as pressure and temperature due to its low-permeability, ductile behavior, and self-healing properties in comparison to other rock formations (Chen et al., 2013; Yin et al., 2019). Rock salt formation may experience cyclic loading conditions either by natural periodic dynamic loads such as earthquakes or by applied cyclic service loads. A salt cavern experiences cyclic service loads when the pressure of the stored gas inside the cavern fluctuates due to gas injection or retrieval (Fuenkajorn and Phueakphum, 2010; Khaledi et al., 2016; Liang et al., 2012). Although the frequency of the cyclic service loads is significantly small, as normal retrieval or injection does not occur more than once a day, still, these loads are applied to the cavern time after time causing conditions similar to a traditional cyclic test (Voznesenskii et al., 2017). Therefore, studying the behavior of rock salt under cyclic loading conditions becomes intertwined with the serviceability of salt caverns.

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