On Limit Analysis of Surrounding Rock Pressure on Shallow Tunnel under Non-bias and Bias Conditions

Considering 2 conditions for shallow tunnel—non-bias and bias,according to the collapse modes used in Terzaghi method and Code for Design of Road Tunnel together with practical engineering experience, a new collapse mode which is closer to actual situation and more rational is put forward. The upper bound method of limit analysis is used to derive the theoretical formulas of surrounding rock pressure on shallow tunnel under the new collapse mode,and the theoretical formulas are transformed to a computation model to search for the maximum value of surrounding rock pressure. Combining with the calculation examples and utilizing Matlab,the optimizing solution of the computation model is obtained through sequential quadratic programming,and the solution is compared with both previous results and the result calculated by limit equilibrium method. It can be seen that the upper bound solution computed by limit analysis upper bound method under the new collapse mode is very close to both previous results and the result calculated by limit equilibrium method for shallow tunnel. It is practicable to solve surrounding rock pressure on shallow tunnel by using upper bound method of limit analysis. What is more,the new collapse mode for non-bias and bias conditions respectively is reasonable.