Angular measurement errors in underground mine surveying reference networks

Surveyorʼs reference networks are the main geometric basis of all underground surveys and consist of polygonometric courses laid, as a rule, along capital and main mine workings. When laying polygons along mine workings, horizontal angles between each two adjacent sides of the course, inclination angles and lengths of the course sides are measured. Each measurement is performed with some error, which eventually leads to errors in determining the coordinates of polygon points. The peculiarities of underground polygonometric courses due to their forced configuration determined by mine workings, the presence of forced short sides and a limited number of starting points, contribute to the rapid accumulation of errors in the course as the distance from the starting points. The accuracy of measurements in the polygonometric passes, laid in the construction of underground reference networks, is characterized by the general normative indicators: the mean square error of measurement of horizontal angles of 20", vertical angles – 30". According to the requirements of the current normative instructions, the measurement of angles in underground polygonometric passages should be made with theodolites of T15 type or theodolites with the accuracy of the reference device not less than 15". The last requirement applies to theodolites of T30 type. In polygonometric moves laid along the mine workings with an angle of inclination of less than 30 °, the angles are measured in one repetition or reception. Measurement of angles in mine workings with an inclination angle of more than 30 ° is recommended to perform a method of techniques (at least two), observing the following rule: before each technique set the vertical axis of rotation of the theodolite in a plumb position and re-centering the device. If we proceed only from the instrumental component of the total error of angle measurement to ensure the mean square error of horizontal angle measurement ±20" theodolite type T15 should perform angle measurement in one full method, and theodolite T30 – in three methods. Instrumental error of angle measurement is caused by errors of sighting, counting, eccentricity of the limb and alidade, incorrect geometry of the horizontal circle, non-verticality of the theodolite rotation axis. The studies of errors in measuring horizontal angles in underground surveyorʼs polygonometric courses made it possible to draw the following conclusions: – the recommendations of the instruction «Surveyi