Study on Quantitative Evaluation Criterion for Stability of Tunnel Surrounding Rocks in Upper-soft and Lower-hard Strata

For 5 groups of strata composed of surrounding rocks of common grades,a detailed analysis and systematic study on the quantitative evaluation criterion for the stability of tunnel surrounding rocks in upper-soft and lowerhard strata was carried out by finite element numerical calculation.The double indexes of crown displacement abrupt variation criterion and the safety factor reflecting the nature of tunnel failure were determined to identify the stability of tunnel surrounding rock.The self-stability of surrounding rocks under various combinations of 5 groups of strata was studied by a large number of numerical experiments,a quantitative grouping of rock mass stability was defined by the self-stability curve,and a quantitative evaluation criterion for stability of surrounding rocks was established.The research results play a role of refinement and supplement to the research of classification theory of stability of surrounding rocks in civil engineering field.