Modeling the pipe umbrella roof support system in a Western US underground coal mine

Weak roof conditions in underground coal mines are a common occurrence and cause significant problems in delaying production. This work presents innovative way of using directional drilling method for roof support in weak sandstone conditions other than conventional method such as bolting, trussing, and cribbing methods. This paper presents a conceptual model of pipe umbrella roof support methods intended for employment in the underground coal mining environment over a single entry of a development section. The design methodology was evaluated by examining a case study of a western U.S. coal mine, and its specific geologic conditions. This work used extensive literature reviews and laboratory test results of the mine. Geotechnical laboratory testing was performed for a weak sandstone channel material that occurs in large extents at the mine for input into numerical models. 2D and 3D models in FLAC were developed. These models utilize beam elements embedded in the continuum model. Results from the modeling showed that bending moments vary in the embedded beams based on the pipe spacing and the diameter of the pipes. A design criterion for a pipe umbrella system was based on the developed bending moment due to undermining and the commonly used flexure formula for bending stress. A safety factor approach was used in this paper for the design of a pipe umbrella system. ► We propose the innovative way of using directional drilling method for roof support in weak sandstone conditions for an underground western coal mine. ► We examine the proposed model with back envelop calculation and Numerical simulations using 2-D and 3-D models in FLAC. ► Numerical simulation is developed based on geology historical data and laboratory test results of the mine. ► We suggest the effect of pipe spacing and the diameter of the pipe on safely designing a pipe umbrella system.