Modeling Spatial Variance and Investigating the Effects of Variability on Intact Rock Strength and Stability of Entries
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Modeling Spatial Variance and Investigating the Effects of Variability on Intact Rock Strength and Stability of Entries in a Longwall Mine Danqing Gao 1
&
Brijes Mishra 1
Received: 26 March 2020 / Accepted: 8 July 2020 # Society for Mining, Metallurgy & Exploration Inc. 2020
Abstract Spatial variance of rock properties is an important characteristic of rock which addresses the heterogeneity of mechanical and physical properties and their effect on underground mining. Assessing spatial variance can be useful for both locating potential difficult grounds and performing reliability analysis in the mining support system. This study shows a microscale numerical model for rock material based on continuum mechanics. To consider the spatial correlation factor of mechanical properties in realistic rock mass, this study introduces a spatial correlation concept into the traditional type III extreme value distribution model. Based on the improved microscale random model, we conducted a series of numerical uniaxial compressive tests and one longwall mine model to investigate the progressive failure of rock. The results show that spatial correlation factor can significantly affect the load-deformation curves and fracture patterns. The spatial variance model was applied to a longwall mine that included several cutting sequences to observe the influence of the spatial variance on roof behavior. The cohesion and friction random fields induced failure that propagated randomly through the immediate roof in different entries. The results showed that the spatial variance provides an accurate prediction of erratic roof falls in coal mines. Keywords Spatial variability . Correlation length . Crack propagation . Extreme value distribution . MATLABĀ® . FLACĀ®
1 Introduction In rock engineering, accurate strength prediction of rock mass is imperative for a successful design, especially for an underground structure. Complex depositional activity in the rock formation process causes the rock to be heterogeneous. Heterogeneity affects the physico-mechanical behavior of rock. The inherent variability of rock is one of the major sources of uncertainty that also causes strength variation in intact rock. Researchers often use the deterministic approach in solving rock mechanics problems. Researchers can use single mean values of limited site data to estimate the intact rock parameters, such as the strength and deformation modulus [1, 3, 11]. However, the estimations are always questionable, as the deterministic methods ignore the inherent variation in the intact rock. This study investigated the effect of heterogeneity at two scales, rock mass (immediate roof a longwall coal mine) and
* Danqing Gao [email protected] 1
Department of Mining Engineering, West Virginia University, Morgantown, WV 26505, USA
intact rock scale. Researchers often determine rock strength in the laboratory either by coring the specimens from the rock blocks or the cores retrieved from the mine sites. The standardized tests recommended for a mine design involve ty
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