Adaptation assessment of gob-side entry retaining based on geological factors

• Eighty mark results were used to analyse 6 geological factors' weights.
• Dip angle is the most important geological factor for gob-side entry retaining.
• Five grades were created and their support methods were recommended.

The technique of gob-side entry retaining has been widely used in underground coal seam mining, where the headgate of current panel is retained and reused for adjacent next panel mining. To evaluate the adaptation of this technique, six geological factors, including coal seam dip angle, mining height, cover depth, thickness influence coefficient of immediate roof (TICIR), lithology of immediate roof and roof integrity, were determined, and their distribution characteristics in practice and weight analysis using 1–9 scale method of analytic hierarchy process (AHP) were used to apportion weight of indicators. It is found that, among all indicators, the dip angle had the highest weight while the buried depth had the lowest weight, indicating that the coal seam dip angle is the most important factor. Moreover, five adaptive grades were classified and gob side support strategy for entry of each grade was provided according to technical standards, statistical information and field experience. Finally, fuzzy comprehensive evaluation was used to weight the gateway adaptive grade index. The adaptation assessment grades may be evaluated as reasonable and scientific by six validated cases. Therefore the proposed method and framework can be considered as a supplementary tool in design of gob-side entry retaining.