Humidity Effects on Coal Mine Roof Stability.

摘要

This report summarizes the results of an investigation into the causes of coal mine roof instability caused by the environmental characteristics of the air ventilated through a mine. The field studies,which were mostly in the Illinois Coal Basin,concentrated on collecting data of surface weather conditions,mine air characteristics (relative humidity and temperature),roof material types,roof movements,and characteristics of roof deterioration. The field studies revealed seasonal changes in weather are reflected in the mine air. The intake air undergoes rapid tempering along its course as it interacts with the ambient mine conditions. There are seasonal moisture interchanges between the mine rock and air,and a mine will lose more water than it gains on a yearly basis. The field studies also established that when the roof rock is shaley,seasonal changes in the humidity will cause roof deterioration because of the detrimental action of moisture on the shale. Roof falls were inventoried and classified by geometry. In the laboratory investigations,physical tests proved unreliable for evaluating shales for roof stability. The Franklin slake test lacks the sensitivity needed to differentiate shale durability for roof stability. A relative humidity test that reveals the sensitivity of a shaley rock to moisture change was devised. Environmental chamber studies showed that neither temperature nor barometric pressure have a direct influence on shale durability. Photoelastic studies showed that the rate and depth of moisture absorption into a shale is controlled by bedding planes,fractures,and holes interrupting the exposed surface.