Improvement of the U-shaped steel sets for supporting the roadways in loose thick coal seam

This paper aims at improving the traditional U-shaped steel sets to efficiently support and stabilize the roadways in loose thick coal seam. The proposed supporting structure is an integrated shed system which is based on backfilling of chemical grouting material behind yieldable steel sets, i.e., metal mesh plus backfilled chemical grouting material plus double resistant geomembrane plus U-shaped steel sets. For implementation and verification, field experiments along with stress and deformation monitoring were conducted in the ventilation roadway of a top coal caving mining face. The results show that the proposed strategy can successfully solve the problems of roof fall, floor heave, large deformation and support damage of roadways in loose thick coal seam. In addition, comparing with the conventional supporting system of U-shaped steel sets, the improved system can also achieve a relatively faster excavation speed and reduce the overall support cost. ► U-shaped steel sets were improved to support roadways in loose thick coal seam. ► Backfilling chemical grouting material and adding inverts are key innovations. ► This strategy can solve problems of roof caving, floor heave and support damage. ► Site monitoring has proved the effectiveness of this improvement. ► Practice also showed that excavation was accelerated and cost was reduced.