Abstract: Using RMR(rock mass rating)and Hoek-Brown(H-B)criterion to estimate mechanical parameters of rock mass is an effective way to determine parameters of the surrounding rock mass around large underground cavern. Considering that the uncertainty of input parameters directly affects the estimation accuracy of mechanical parameter of rock mass， relying on the large underground powerhouse engineering of Baihetan Hydropower Station， the sensitivity between the input parameters of H-B criterion and mechanical parameters of rock mass is studied through in-situ test， laboratory test and numerical simulation， in which the sensitivity factor is used to describe the sensitivity relationships. The results show that the sensitivity of mechanical parameters of rock mass to input parameters is ranked as RMR>σ_ci(uniaxial compressive strength of rock)>m_i(rock material constant)， and the influence of RMR is the most significant. The error of ±5% in the determination of RMR would result in a deviation of about 20%， 22% and 13% in the estimated results of elastic modulus， internal friction angle and cohesion， respectively. When the error of σ_ci and m_i is less than ±20%， the influence of them on the estimation results of internal friction angle and cohesion is less than 4% and 10%， respectively. This research can provide reference for the accuracy evaluation on estimation of mechanical parameter of rock mass around similar large underground caverns.

Key words: Hoek-Brown criterion； mechanical parameters of rock mass； large cavern； sensitivity factor； error analysis