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Successful roof control systems in underground coal mines with weak roof are often difficult to design. If the rock is very weak, additional problems can result from geological characteristics such as thinly laminated and water-sensitive rocks, which in turn can compound the time-dependent roof stability. Roof failures such as cutters, pot-outs, massive collapses and cracks between bolts are common in coal mines with weak top. Unstable roof conditions can result if the roof support system is not designed for these failures. A two-year study of weak roof data from U.S. coal mines, including field studies, lab testing and numerical modeling, was performed. The study has added new insights into ground-control considerations. Follow up studies of geological conditions and roof failure modes were carefully observed. Fully grouted resin bolts and tensioned bolts were modeled to compare their performance in weak geologic conditions. Critical requirements such as bolt type, length, spacing and capacity are presented for optimal roof support in coal mines with weak geological roof conditions. [ABSTRACT FROM AUTHOR]