It is known from the analysis and research on 162 roof-falling accidences occurring in coal mining roadway supported by bolts that the deteriorative combination of roof strata is the major reason that accounts for percent 66 of the total accidences. RFPA2d system (the system of rock failure process analysis

developed by Northeastern University) is used to simulate the deteriorative process of different strata combination roof. The result suggest that the deterioration of strata combination is related to the change of soft interlayer positions

the thickness of hard strata

the ratio of height and span

and the thickness change of soft strata in the direct roof. The deteriorative rupture of strata combination results from the tensile failure

shear failure and their mutual action. Under the action of shear stress

the whole roof falls down; under the action of deadweight stresses

flexural failure of roof strata takes place; whereas under the mutual action of shear stress and tensile stress

the failure configuration of the laminated roof strata presents a form of roof-falling arch.