Study On Progressive Failure Mechanism Of Tunnel Surrounding Rock In Upper-soft Lower-hard Strata And Its Valuation Method

Upper-soft lower-hard tunnel engineering instance increasingly more,China lack for upper-soft lower-hard tunnel of design method,roots is lack upper-soft lower-hard formation tunnel damage mechanism and the evaluation of specifically research,this papers relies on National Science Fund project:upper-soft lower-hard formation tunnel progressive damage mechanism and design method research(51478118),proposed has upper-soft lower-hard formation tunnel surrounding rock damage mechanism and the evaluation this a research subject,main application limit numerical simulation method and related theory analysis,Carried out a systematic study.(1)Through on upper-soft lower-hard tunnel formation tunnel surrounding rock damage factors of research,obtained:tunnel span,and buried depth,and soft hard formation points interface location of sensitive degree gradually reduced,excavation method and dig into size of sensitive degrees most weak;obtained excavation tunnel surrounding rock can since stability,tunnel span is most sensitive factors,tunnel surrounding rock cannot since stability,upper more soft formation physical mechanical parameter is most sensitive factors,second for tunnel span;Hard and soft surrounding rock boundaries spatial occurrence of structural plane characteristics and structure of physical and mechanical parameters of surrounding rock deformation and failure of major impact.(2)Through on upper-soft lower-hard tunnel surrounding rock damage mechanism of research,obtained:upper-soft lower-hard shallow buried tunnel,vault surrounding rock appeared damage and extends collapsed to surface,with buried deep of increased,damage regional gradually to arch shoulder transfer,deep buried tunnel,damage regional by Arch shoulder gradually to vault and side wall parts transfer,last vault,and Arch shoulder and side wall of damage regional Unicom,led to upper more soft formation hole around rock overall lost stability damage;Upper-soft lower-hard formation in the,tunnel surrounding rock stability often by structure surface,and Coupling analysis of seepage of groundwater,which exacerbated the damage and deterioration of rock,prone to upper soft rock arch collapses,heading longitudinal slip instability,lateral slip instability of engineering disasters.(3)Through on upper-soft lower-hard formation tunnel surrounding rock damage evaluation of research,obtained:proposed in design stage,used safety as tunnel surrounding rock stability evaluation of main quantitative index,used limit deformation as tunnel surrounding rock stability evaluation of auxiliary quantitative index;proposed in engineering construction stage,used safety and limit deformation as tunnel surrounding rock stability evaluation of double control quantitative index;for upper for IV,and V level surrounding rock and lower for ?,and ?,and IV level surrounding rock composition of five planted upper-soft lower-hard formation,Proposed safety standards for tunnel surrounding rock and vaulted the maximum settlement value standards,established upper-soft lower-hard formation damage evaluation method of tunnel surrounding rock.Research and findings to enrich and develop China tunnel engineering design,construction and safety management theory is of great scientific significance and practical significance.