A field data-based approach for risk and relative efficiency assessment of rock bolt designs in underground coal mines

Optimizing or revising support systems are inevitable due to the existence of high probabilities and uncertainties in underground mines. For this aim, field data and measurements are the only scales available to truly measure the performance of these systems. This paper presents a site-dependent approach for optimizing/revising the applied rock bolt support systems and estimating the efficiency of installation operation based on the field data for underground coal mines. For this purpose, a comprehensive database containing field data from 128 different mining locations of an underground coal mine was taken into account. At first, the relationships between field data and measured displacement by installed tell-tale extensometers (TTD) in the roof to determine the effective parameters on the roof instability were analyzed. In the following, a method was introduced to calculate the weighting factor of the effective parameters in the system using coefficient of determination (R2) and sensitivity index (SI). The sensitivity index was developed for sensitivity analysis of all considered parameters on TTD under fair conditions. Then, a method entitled field data-based risk index (FDRI) model was presented to evaluate the risk of roof instability supported by rock bolt systems which was validated by the considered case study. Finally, a process was proposed to optimize/revise a rock bolt design using the results of FDRI model and introduced data-driven efficiency (DDE) theory. DDE theory was provided to relative estimation of the efficiency of the installation operation of rock bolts. This research presents a systematic method for selecting the effective parameters on an issue or hazard, determining their weight in the system and carrying out relevant ratings needed for risk assessment.