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Abstract For a long time，stability evaluation of underground tunnel is unreasonable and unscientific. Safety factor of cave cannot be got by classical finite element method and it is difficult to judge the stability of tunnel by the criterion of stress，displacements of tunnel perimeter or size of plastic zones of surrounding rocks. Therefore，strength reduction technique is conducted to solve the stability factor of tunnel floor. Ultimate analysis is essentially a strength problem，so different strength criterions would cause different results. In view of this，relationship of strength parameters of different yield criterions are put forward and conversion expressions of the shear safety factors between classical Drucker-Prager(D-P) criterion and extended D-P criterion were obtained based on plane strain assumption. Considering that floor heave is caused by the general shear failure by compression effect of rock mass of tunnel walls，stability safety factors and potential failure surface of soft rock tunnel floor were analyzed according to the damage criterion of displacement catastrophe based on strength reduction finite element method，and results were compared with respect to different yield criterions. The results show that，theory conversion methods of safety factors have higher accuracy. Relationship of safety factors solving by different criterions are DP1＞M-C＞generalized D-P＞DP2＞DP4＞DPM-C＞DP3，which shows result of DP1 is in unsafe side and the results of DP2，DPM-C，DP3 are in good agreement with each other. Grid density and dilatancy angle have great influence on the results convergence.
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Received: 16 April 2012
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2012, Vol. 31 
