According to the characteristics of long span underground engineering’s complex structure and high safety risk

the paper establishes a synthetically evaluation system by theoretical analysis

numerical simulation and experience evaluation. Through a variety of plastic mechanical calculation method

the Caquot formula

Fenner formula

modified Fenner and Kastner formulas are applied to project practice; select one method is most suitable analyze way for large span structures in hard rock. Using Q system and engineering analogy

determine the supporting parameters of anchor bolt in large-span underground engineering. The length of anchor bolt depends directly on the excavation span in Q system

at same time we can get support parameters of shotcrete. By analyzing the same level span underground works

determined that cable length should longer than 40% of the underground work’s span. Through the three-dimensional discrete element to evaluate the stability of supporting structures. In numerical calculations

rock strength criterion can be defined by the strain-softening model of HB. Constitutive relations of structural surface can use ideal elastoplastic model in Mohr-Coulomb strength criterion. After applying three rows of prestressed-cables at the upper side wall

the of deformation of side wall is significantly reduced. At the same time

the number of potential instability surrounding rock mass and scope are effective significantly controlled. By stress analysis of supporting structure，it is show that the 60% of the anchor’s axial force is between 2.0-2.25 MN; the underground engineering has a good safety. Through the synthetically evaluation system including plastic area analysis

numerical simulation and experience analysis

the formation of three-in-one evaluation system is reached. This system can be used for large-span support structure’s rationality evaluation. Through the analysis

The supporting design scheme can effectively deal with the failure phenomenon of rock block stability risk. In local lowly safety parts

anchor and anchor-cable stress level is comparatively high

can reduce the anchor-cable’s pretension force and increase the number of random anchor.