Hazard evaluation of mining terrain based on horizontal strain survey

This paper presents a case study focused on the measurement of horizontal deformations occurring above an active coal seam extraction site in the Upper Silesian Coal Basin. The investigation of ground surface deformation effects was carried out along a randomly selected 48-meter test section located above a mining panel. Within the defined segment, the deformation index values were determined using measurements based on varying base lengths, ranging from 1 to 24 meters. The primary objective of the study was to identify the actual magnitudes of horizontal deformations that developed within these bases during the course of the deformation process. The main source of data consisted of measurements of distances between permanently stabilized survey points positioned at 1-meter intervals along the observation line. These measurements were obtained using a specially designed and constructed instrument. The values of the deformation index, depending on the length of the measurement base, resulted in significant differences in the assessment of surface stability and potential hazard within the same area. The horizontal deformations determined from 6-meter and standard 24-meter bases did not fully capture the actual deformation hazard affecting the ground surface. The presented case study demonstrates an irregular spatial distribution of horizontal deformations within bases of 6 meters and longer. The maximum deformation index values recorded over shorter segments considerably exceeded the averaged values, leading to changes in the evaluation of the mining area’s deformation risk at the study site.