deep mining of coal pillar
stability of coal pillar
stress of coal pillar distribution
stressmeter of coal pillar
two kinds of coal pillar
Coal pillar for protection of buildings
coal pillar for protection of builings
anterior pillar of fauces
boundary coal-pillar
边角煤
支持向量机(support vector machine,SVM)
coal pillar for sand proof
coal pillar for water preserving