1. 〈http://www.msha.gov/stats/charts/coal2011yearend.asp〉, 2013.
2. Moebs NN, Stateham RM. Geologic factors in coal mine roof stability-a progress report. USBM IC 8976, 1984, 27 pp.
3. Molinda GM, Heasley KA, Oyler, DC, Jones JR. Effects of horizontal stress related to stream valleys on the stability of coal mine openings. USBM RI 9413, 1992, 92–97.
4. Enever JR, McKay J. Stress measurements at Nattai North Colliery and their interpretation in terms of sedimentological and topographic features. CSIRO Rep 29, 1980, 27.
5. Bauer ER. The effects of valleys on the strength of rock materials at depth. In: Proceedings of the 28th U.S. symposium on Rock Mechanics, Tucson, 1987, p. 345–389.