Experimental validation of a laser distance measurement system for convergence monitoring in underground salt formations

This study evaluates the metrological performance and statistical reliability of a laser distance measurement system developed for convergence monitoring in the Kłodawa Salt Mine S.A. The standard deviation of single distance measurements was determined for sighting lengths from a few to nearly 50 m under controlled laboratory conditions and during underground field tests. Measurement uncertainty propagation was applied to determine the minimum detectable annual change in baseline length at confidence levels of 95–99%. Laboratory measurements demonstrated high stability, yielding standard deviations between 0.18 and 0.38 mm. Despite the challenging underground environment, field measurements maintained standard deviations below 0.7 mm for baselines up to several tens of meters. The analysis shows that for baselines ≤30 m, the system enables detection of convergence as small as 2 mm/year, with detectability increasing nearly linearly to 5 mm/year at 43 m and 8 mm/year at 49 m. Comparison with electronic total stations confirmed comparable performance on short baselines, with the laser system offering advantages in operational efficiency and setup simplicity. The results represent the first comprehensive metrological validation of a laser distance measurement system used in deep underground mining conditions and demonstrate its suitability for long-term, high-precision displacement monitoring in deforming rock masses.