Mining Publication: Evaluation of Polymer Construction Material and Water Trap Designs for Underground Coal Mine Seals

Strength characteristics and air leakage resistance of seals and designs of water traps used in underground coal mines were evaluated in a joint effort by the Pittsburgh Research Center and the Mine Safety and Health Administration. The efficacies of various seals in limiting air leakage from a sealed area following an explosion were tested at the Lake Lynn Experimental Mine. Polymer seals composed of a mixture of polyisocyanate and polyol resins were used in a composite structural design in which they were placed between two dry stacked hollow core, concrete block walls. Seals constructed using 76, 46, and 31 centimeter (cm) thick polymer and stone aggregate cores survived an explosion pressure of 145 kilopascal (kPa) and maintained acceptable leakage resistance. Only the 46-cm thick seal survived a pressure pulse of 269 kPa. A seal 97-cm thick with a density of 91 kilograms/cubic meter (kg/m³) constructed with polymer without aggregate did not survive the explosion, whereas a 51-cm thick, 203kg/m³ polymer only seal successfully withstood the explosion pressure. Seals consisting of cellular concrete injected with polymer slurry using a two pour injection process were able to withstand the explosion pressure. Two seal designs using low density cementitious block were also found to be effective. Additional studies demonstrated that three commonly used water trap designs were ineffective under worst case conditions. Improvement was seen with the installation of an additional course of block around the water trough area on the active side of the seal and by lowering the trap opening through the seal.