Masoud Ghaemi - PhD student, Department of Rock Mechanics, Islamic Azad University, Science and Research Branch, Tehran, Iran
Mohsen Mousivand - Islamic Azad University, Gonbad Kavoos Branch, Dept Civil Engineering, Gonbad Kavoos, Golestan, Iran

Geotechnical factors influencing pillar strength and overburden stability are analyzed in this paper. Thework highlighted the importance of geological, mining and design factors The influence of design factorsis quantified using FLAC as well as load transfer data from U.S. coal mines. Dynamic effects areanalyzed using UDEC showing how marginally stable pillar designs could fail as dynamic stress istransferred over a 120 m wide barrier. Popular empirical methods are evaluated while proposing meansfor accounting for confinement. New data are included for weaker coal seams in soft tertiary strata of thestudy site at shallow cover

dynamic loading, pillar strength, load transfer, horizontal stress