Investigation into the strength of iron ore pillars in the Lorraine basin

Iron ore mining was carried out in the Lorraine district in the north-east of France for several centuries. The predominant mining method was bord and pillar, with pillar extraction in some areas. The orebody consists of several layers and mining was done on multiple levels. There is no evidence today that a formal design method for pillar size was in use. Mining ceased in 1975. It is important to evaluate pillar stability and hence surface stability as the region has been extensively built up. It is an important input parameter in the surface stability risk analysis that is done for all historical mining areas in France by INERIS. The method used to determine the optimal strength formula for coal pillars in South Africa has been used successfully for the iron ore pillars in the Lorraine basin in France. The method is based on obtaining the best possible distinction between cases of failed and stable pillars using the safety factor and arriving at a mean safety factor of 1.0 for the population of failed pillars.