According to roof collapse characteristics of large section roadway with thick top coal

a failure mechanism of roof collapse block

considering the influences of the stress of surrounding rock and supporting pressure

was constructed based on Hoek-Brown failure criterion and its associated flow law. Through upper bound limit analysis

the roof collapse mechanism of large section roadway with thick top coal was deduced with variational principle; and with one roadway in Zhaolou coal mine

for example

the influences of rock parameters on roof collapse mechanism were also analyzed. The calculation results show that: With the increasing of empirical parameter A

tensile strength

compressive strength and supporting pressure

the size of collapse block increases

while decreases with the increasing of empirical parameter B

the stress of surrounding rock and unit weight of rock mass. The size of collapse block represents the roof stability

larger size means more external work to expend

and the roof is more stable. The parameter B

the stress of surrounding rock and supporting pressure have significant impacts on roof collapse mechanism; and the parameter B determines the shape of failure curved surface; the curvature of failure surface will decrease with the increase of parameter B. Improving supporting pressure is an effective way to increase the roof stability

which provides theoretical basis for the support design of large section roadway with thick top coal.