Abstract:

The paper reviews three tunnel design methods used at present and puts forward the stratumstructure method based on numerical limit analysis. The method can work out the safety factor of surrounding rock needed in the design, so the current subjective problems can be solved. The paper studies the separatrix between shallow tunnels and deep tunnels and also evaluates the advantages and disadvantages of the two dividing standards. Five basic ideas of tunnel design and calculation are discussed in the paper: 1) The tunnel design must satisfy the safety requirements during operation and construction and the safety factor of surrounding rock after primary support must ensure the construction safety; 2) The design and calculation model should adapt to different geological conditions, different surrounding rock pressure characteristics and different practical mechanical state of the tunnel; 3) The design and calculation of tunnel must be in accordance with the modern pressure theory of surrounding rock and supporting principle and must make full use of the selfsupport capability of surrounding rock; 4) The tunnel structure model should also adapt to the practical mechanic state and the new idea that the primary support is the reinforcement material of surrounding rock and that calculation should be made according to the plastic theory should be established; 5) Reasonable calculation method and calculation parameters should be used to ensure scientific tunnel design and calculation. Finally, taking a subway station as an example, the paper introduces the design method of tunnels in Grade II, Grade III and Grade V surrounding rock.

Key words: stability analysis, analytic criteria of the stability of surrounding rock, FEM strength reduction method, safety factor of shear, failure surface, soil tunnel, rock tunnel