Effects and controls of lateral refraction in underground coal mines

Abstract

[Abstract]: Environmental conditions in underground coal mines effect lateral refraction when surveying with a regular theodolite. Xstrata Coal’s Oaky North Mine situated 26Km east of Tieri in Central Queensland’s Bowen Basin has overcome these environmental conditions by utilising gyrotheodolites to control the underground survey network. This project studies the environmental conditions effecting lateral refraction and how Oaky North Mine utilises gyrotheodolites to control the underground survey network. Oaky North Mine is an underground longwall coal operation, producing approximately 5 million tonnes of sub-bituminous, medium volatile coal per annum. Two pairs of parallel tunnels (gateroads) with cross cuts every 100m are driven using a continuous miner for a length of approximately 3.4 Km. These gateroads form the maingate and tailgate of the longwall block. The demand for an accurate underground control network is high. Typically, accuracies of ±50mm are expected allowing a breakthrough tolerance of ±100mm. The ability to establish accurate control networks and perform associated surveys is restricted by lateral refraction. The path of light through the atmosphere is influenced by the inhomogenities of the refractive index. This refractive effect deteriorates the pointing accuracy of survey lines. Currently, there is no available method to accurately correct these systematic errors. This project investigates whether literature research supporting the use of a gyrotheodolite, will improve breakthrough errors of an open ended traverse or when compared to the readings from TCRA 1203 vary sufficiently to be outside accepted tolerances. Specifically, in this project, the gyrotheodolite used is the DMT (Deutsche Montan Technologie) Gyromat 2000, permanently fixed to a Wild T2 theodolite. The Gyromat 2000 is a fully automated high precision (1.5cm every 1Km) surveying gyroscope with a measuring time < 10mins.