Study On Rock Failure Characteristics And Rock Strength Criteria Under High Confining Pressure

High in-situ stress is increasingly prominent as the underground mine gradualystepped into deep mining stage, which caused rock burst, water inrush, stope instabilityand a series of severe accidents occurred frequently and even had an anabatic trend.Meanwhile, the nonlinear characteristics of rock strength under high confining pressurecondition could not be described and characterized accurately by traditional rock strengthcriteria, which are the important theoretical foundation and scientific basis of rockengineering excavation design. Based on the problems above, the typical Ezhou granite ofWISCO Chenchao iron mine is selected as subject to carry out rock triaxial experimentresearch and strength criterion theory research under different confining pressureconditions. The main contents and conclusive results are as follows:(1) Study of rock failure characteristics under high confining pressure condion. Basedon the Ezhou triaxial experiment results, discovered rock ductile failure characteristics isthat the deviatoric stress and strain curve becomes smooth after linear elastic stage,entering plastic flow state, and appears as a horizontal line before failure, and the plasticstrain becomes larger with the confining pressure increasing. Meanwhile, discovered thatrock failure type changes from shear failure at low confining pressure condition to shearfracturing composite failure at high confining pressure condition, and rock failure formchanges from single fracture surface to multiple fracture surfaces, and also discovered thatrock failure fracture angle becomes smaller with the confining pressure increasing. Rocktriaxial strength characteristics was also explored, and defined the concept of rock criticalstate confining pressure, obtained that when rock failed at critical state confining pressure,the difference value of1and3is constant, and would not change with the confiningpressure increasing. Through using Ezhou granite experimental data verified that MCcriterion is suitable for low confining pressure condition, but could not reflect thenonlinear characteristics of rock traxial strength under high confining pressure.(2) Research on application scope of non-linear MC criterion and its improvement.Through analysing the application scope of non-linear MC criterion, proposed a newcriterion called I-MC criterion. By using12kinds of rock triaxial experiment data verifiedthat I-MC criterion has a higher accuracy than non-linear MC criterion, and it also has a larger application scope. Moreover, I-MC criterion applied under true triaxial compressioncondition is preliminary studied.(3) Study of rock strength criterion suitable for high confining pressure condition.Proposed a new criterion called rock hyperbolic strength criterion, and its yield curve inplane and yield surface in principal stress space were derived. By using12kinds of rocktriaxial experiment data verified that hyperbolic criterion has a preferable applicability.Moreover, hyperbolic criterion applied under true triaxial compression condition ispreliminary studied.(4) Research of HB criterion improvement under triaxial compression condition.Proposed a new criterion called I-HB criterion. Compared with HB criterion, it has moreobvious nonlinear characteristics and its accuracy increased markedly. By using12kindsof rock triaxial experiment data verified that I-HB criterion has a higher accuracy thanI-MC criterion and hyperbolic criterion. Moreover, I-HB criterion applied under truetriaxial compression condition is preliminary studied.(5) Accuracy comparative study of rock strength criteria. The accuracy of proposedrock strength criteria, I-MC criterion, hyperbolic criterion and I-HB criterion, werecompared with some criteria which are regarded as outstanding criteria in rockengineering. The compared results showed that the proposed three rock strength criteriaare all have higher accuracy. Especially, the I-HB criterion could evaluate rock triaxialstrength in the highest precision.Through the above researches, revealed rock failure and triaxial strengthcharacteristics under high confining pressure condition, improved the traditional strengthcriteria, and even put forward a new criterion which is suitable for high confining pressurecondition. It is aimed at providing guiding significance and theoretical reference for deeprock engineering excavation design and deep rock mechanics development.