An analytical solution to tunnels with over-under-excavated surface based on perturbation method

The tunnels excavated using drilling and blasting often results in a very irregular and rough excavation surface,its influences on the stress of surrounding rock were neglected for adopting a regular and smooth excava-tion surface in tunnel analysis model.Considering the over-under-excavated values as little parameter,an elastic stress solution of circular tunnel under hydrostatic pressure is reached based on perturbation method. Conclusions made from the solution as follows: the stresses of surrounding rocks near opening surface vary with over-under-excavated values,the variation of stress relates to the amplitude and slope of the curve of over-under-excavated;the point of the maximum circumferential stress variation locate in the opening surface,stress concentration coefficient reach local maximum and minimum values at the peak of over-excavated and under-excavated part in the sur-rounding rock respectively,the point of the maximum radial stress variation is near the opening surface,at the in-tersection point of over-excavated and under-excavated surface,the shear stress variation reach its maximum values.the stresses induced by irregular and rough surface decrease rapidly in the radial direction,the disturbed areas is about 1~2 times the radium of tunnels.