Application of gyrotheodolites in the determination of bearings for the hozirontal control network of Nui Beo underground coal mine

In Vietnam, coal mines are exploited deeper and deeper, and the method of seams opening using with mine shafts has been increasingly popular. For mine surveying, there are several methods of conveying the bearing to the tunnels, depending on the number of mine shafts, the depth and the cross-section of the shaft, and the available surveyring equipment of the mine. Each method has its advantages and disadvantages, and different application conditions. It has been proved that the method of conveying the bearing to the tunnels or underground orientation by traditional methods gives low accuracy, requires a lot of time and effort, and no assurance of accuracy. The method using a gyrotheodolite has the advantages of reducing time and effort and improving the level of safety. Therefore, the application of surveying gyro is considered as an effective alternative in this work. The paper presents the results of the application of a GYRO X II gyrotheodolite in determining bearings at -140 m and -350 m of the Nui Beo coal mine in order to improve orientation accuracy. The resulting bearings of the first lines of the 2-level underground traversing control networks were used to determine control points at the -140 m level and the -350 m level. The results proved the accuracy of the method with the biggest azimuth error of 9.23”, meeting the accuracy requirement of the Vietnamese standard for mine surveying.