Energy Partitioning Following Tensile Failure in Three-Point Loading Tests of Nugget Sandstone Specimens
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Energy Partitioning Following Tensile Failure in Three-Point Loading Tests of Nugget Sandstone Specimens R. D. Weyher1
· M. K. McCarter1 · J. M. Wempen1
Received: 18 July 2019 / Accepted: 26 May 2020 © Society for Mining, Metallurgy & Exploration Inc. 2020
Abstract Beam theory is a proxy for the behavior of intact, deforming roof strata above underground openings. Strong, stiff, intact strata have the ability to store significant strain energy when underground openings have large spans, as is typical of longwall operations. When strata fail, they may release some or all of this strain energy. Released energy is partitioned between fracture, thermal, and seismic energy. The tensile failure surface in simply supported beams is predicted to be free of shear stress. This prediction and the kinematic inability of crack slip during fracture make significant dissipation of energy by friction unlikely. In this study, the failure energy partitioning of Nugget Sandstone specimens is examined. Tensile fractures in specimens were induced using three-point loading tests. Elastic waves emanating from fracture events were recorded using an array of accelerometers. Accelerometers were placed within two crack lengths of the fracture surface, and the acceleration records are similar to strong motion seismic records. Spectral analysis was performed and used to develop synthetic, well-behaved, acceleration signals. Synthetic velocity signals were used to estimate radiated seismic energy generated by fracture. These estimates of radiated seismic energy demonstrate a potential means to constrain the minimum seismic partition. Fracture testing was performed on additional samples to estimate the fracture toughness of the sandstone. Synthesis of this data demonstrate a potential means to constrain a maximum seismic partition. Bounding the seismic partition for this type of fracture event could aid the detection and evaluation of seismicity emanating from longwall operations. Having better information about the location and magnitude of mining-induced seismicity within longwall overburdens could lead to better understanding of extraction sequencing and rock behavior in general. These energy estimates also support the hypothesis that dissipation of thermal energy by friction is small in bending tensile failure. Keywords Energy partitioning · Radiated seismic energy · Fourier analysis · Seismic efficiency · Tensile failure · Modulus of rupture · Nugget sandstone
1 Introduction This work is an extension of published experimental work [1]. The impetus for a series of prefatory experiments was to
The National Institute for Safety and Health (NIOSH) generously provided financial support for this research under NIOSH BAA 2016-N-17733. The findings in this paper are those of the authors and should not be construed to represent any agency determination or policy. R. D. Weyher
[email protected] 1
Department of Mining Engineering, University of Utah, Salt Lake City, UT, USA
observe the character of elastic waves associated with simulated fr
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