Evaluation of directional drilling implication of double layered pipe umbrella system for the coal mine roof support with composite material and beam element methods using FLAC 3D

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Abstract
This study demonstrates possible scenarios of double-layered umbrella pipe system installed over a longwall take down room in a western coal mine, where holes are drilled and cased from an adjacent entry in advance of undermining. Finite difference analysis in FLAC 3D with strain hardening gob model is used because this method is a complex and rigorous way for solving boundary value problems, such stress and strain in a continuum and at an excavation boundary due to undermining. Support system was simulated with two different methods: composite material method and beam element method. We realized that the composite material method is very conservative compared to beam element method. Thus, in the rest of the simulation, we used the beam element method to investigate the effect of different angles of umbrella pipes on the roof support. To validate the modeling results, we compare the numeral modeling results with empirical formula widely used in subsidence calculation. Also, this computer simulation compared displacement of roof between in the presence and absence of this pipe umbrella support system. In this paper, we demonstrated that a relative stiffness increase ∼185% for a reinforced zone can decrease the displacement ∼ 12.5 cm (∼ 5 in.) in the longwall recovery room roof based on results from the equivalent stiffness method. This reduction is a substantial amount, which could be really beneficial to mine operators during mining processes.

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