The stability of gateroads is one of the key factors for the mining process of hard coal by a longwall system. Wrong designed and applied the gateroad support at the stage of drilling, may adversely affect the functionality of the gateroad and the safety of the crew throughout its existence.

The article presents the results of the underground tests and observations such as: convergence of the gateroad, stratification and the fractured zone range in the roof rocks, carried out in four longwall gateroads at the stage of their drilling.

The obtained test results were the basis for the assessment of the possibility of using a convergence control method in the design of the gateroad support. The method is based on three interdependent relationships, such as: Ground Reaction Curve (GRC), Longitudinal Displacement Profile (LDP), and a Support Characteristic Curve (SCC). All calculations were performed using numerical modeling in the Phase2 program, based on the finite element method (FEM).

In longwall absolute methane emission rate forecasting, the range of the destressing zone is determined empirically and is not considered to be dependent on the geomechanical parameters of the rock strata. This simplification regarding destressing zone determination may result in significant differences between the forecast and the actual methane emission rates. During the extraction of coal seams using a system involving longwalls with caving under the conditions of low rock mass geomechanical parameters, the absolute methane emission rate forecasts are typically underestimated in comparison to the actual methane emission rates.

In order to examine the influence of the destressing zones on the final forecasting result and to assess the influence of the rock mass geomechanical parameters on the increased accuracy of forecast values, destressing zones were determined for three longwalls with lengths ranging from 186 to 250 m, based on numerical modelling using the finite difference method (FDM). The modelling results confirmed the assumptions concerning the upper destressing zone range adopted for absolute methane emission rate forecasting. As for the remaining parameters, the destressing zones yielded great differences, particularly for floor strata. To inspect the accuracy of the FDM calculation result, an absolute methane emission rate forecasting algorithm was supplemented with the obtained zones. The prepared forecasts, both for longwall methane emission rates as well as the inflow of methane to the longwalls from strata within the destressing zone, were verified via underground methane emission tests. A comparative analysis found that including geomechanical parameters in methane emission rate forecasting can significantly reduce the errors in forecast values.

Exploitation of hard coal seams by roadway system is applied by two coal mines in southern Poland in Upper Silesian Basin. It is a secondary mining exploitation carries out in safety pillars of urban areas and shafts within mining areas of closed coal mines. Roadway system is the excavation process of gateways which are made in parallel order leaving coal pillars between them. An optimal width of coal pillar makes roadway stable and reduces subsidence of terrain surface. The article presents results of subsidence simulation caused by partial extraction using empirical and numerical methods on the example of one exploitation field of “Siltech” coal mine. The asymptotic state of subsidence was considered after mining ceased in the study area. In order to simulate of subsidence, numerical model of rock mass and model of Knothe-Budryk theory were calibrated. Simulation of vertical displacements in numerical method was carried out using RS3 program by Rocscience based on finite element method. The assumption was made that model of rock mass is transversely isotropic medium, in which panels were designed according to order of extraction of coal seams. The results of empirical and numerical methods were compared with measured values of subsidence at benchmarks along drawn lines (subsidence profiles).

Currently available field rock mass deformability determination methods are rather difficult to perform, due to their complexity and a time-consuming nature. This article shows results of a suitability assessment of a Pen206 borehole jack (a hydraulic penetrometer) for field rock mass deformability measurements. This type of the borehole jack is widely used in Polish hard coal mining industry. It was originally intended only for quick rock mass strength parameters determination. This article describes an analysis and scope of basic modifications performed mainly on a borehole jack head. It includes discussion of results with possible directions for future development of the device.