Discrete Element Modeling of Delamination in Laboratory Scale Laminated Rock
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Discrete Element Modeling of Delamination in Laboratory Scale Laminated Rock Qingwen Shi 1
&
Brijes Mishra 1
Received: 25 June 2020 / Accepted: 3 September 2020 # Society for Mining, Metallurgy & Exploration Inc. 2020
Abstract Laminated rock can delaminate and fail under certain stress states. Delamination-caused roof fall and cutter roof failure is a common failure mechanism in roadways in Pittsburgh coal seam due to the existence of laminated shale roof. Two-dimensional numerical models were developed at laboratory scale based on the bonded particle method in order to simulate the delamination with particle flow code. In these models, an assembly of bonded particles and parallel weak planes represents the laminated rock. This model calibrated the micro-parameters of the bonded particle material and weak planes with laboratory data. The mechanism of fracturing and delamination in a laminated specimen was investigated using unconfined and confined compression test and unsupported roof compression test. The numerical results show that, under a constant horizontal stress, delamination occurs when the stress is much lower than its compressive strength. The confined compressive test indicates that delamination is restrained by applying confining stress since delamination-caused failure does not occur during any stage of the confined compressive test. Unsupported roof compression tests showed propagation of cutter roof failure with initiation of cracks and delamination at the intersections of the roof and ribs. An outer failed zone and inner failed zone form separately. The separated zones connect and form an opening in the roof. The presented numerical results provide additional insight into process of delamination. Keywords Discrete element modeling . Laminated rock . Delamination mechanism . Cutter roof failure
1 Introduction Pittsburgh coal seam has many longwall mines that experience frequent roof falls. The seam is overlaid with laminated shale rocks. Stack rocks are also common in coal measures strata in south West Virginia. These rocks are not structurally or geologically different from each other as they belong to the same rock type. Field observations show loss of cohesion between the laminated and stack layers. Observations from previous research have shown delamination and cutter roof failure in the roof rock [1]. The current understanding of the structural failure in these rock types is poor. Therefore, a detailed research effort is necessary in order to understand the mode of failure of laminated rocks. There is a significant amount of literature focused on bedded and layered rock. However, there is a difference between
* Qingwen Shi [email protected] 1
Department of Mining Engineering, West Virginia University, Morgantown, WV 26505, USA
lamination and beds in the rock. Lamination refers to parallel layering within a bed. By definition, the bed is thicker than 1 cm, and a lamina is thinner than 1 cm [2]. Previous researches have rarely mentioned the difference between bedding and lamination.
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