Study Of Ringlike Splitting Failure Of Rock Cylinders And Its Related Mechanical Behavior Under Unloading Condition After High Compression

Zonal disintegration in deep underground surrounding rock mass is the engineering background and research subject of this dissertation. Based on the unloading experiments of thick-walled cylinder rock samples after high compression, this research is focused on ringlike failure mechanism in thick wall (unstable distribution at energy peak-value point and energy judgment criteria) and axial splitting failure mechanism of rock cylinders under unloading condition after high compression. It also studied the related mechanical behavior about the unloading failure of rock cylinder after high compression such as scale effect of rock failure, rock burst tendency of unloading failure and structural effect of rock failure. The research results can supply reasonable explanation of zonal fracturing mechanism and theoretical foundation for the supporting of similar roadways to keep the structural stability.Research contents and methods are as follows:(1) The description of rock structural plane and the measurement of basic physical and mechanical behavior were firstly performed. The scale effect of uniaxial compressive strength was also studied. These results were the basis of description of rock physical and mechanical behavior and supply accurate mechanical parameters for setting up the real triaxial energy criteria in the following.(2) Based on the stress change characteristics of surrounding rock mass in deep underground engineering (loading to unloading), the unloading experiment of rock cylinders after high compression was performed. Ringlike failure in thick wall of rock cylinder was studied by this experimental method.(3) The real triaxial energy criteria taking account of the influence of intermediate principal stress on energy release was set up and validated by the three principal stresses of ringlike failure in rock cylinders.(4) Taking account of the influence of unloading damage on the variation of three principal stresses, ringlike fracturing mechanism was studied based on the energy principles.(5) Based on the stress variation, axial splitting mechanism of rock cylinders under unloading condition after high compression was studied by the Griffith theory.(6) Based on the energy release condition of two basic failure modes of rock strength failure, rock burst tendency of rock unloading failure was studied.(7) Based on the structural effect of rock failure, the relation of intact loading structure of rock cylinders and the occurrence of ringlike failure was discussed. Based on RFPA2D, the fracturing structural effect after deep surrounding rock failure was studied by numerical simulation. Producing location and formation condition of remote cracks in the middle part of rock was studied.The main innovative achievements were obtained as follows:(1) Ringlike failure pattern with highly tensile behavior was obtained under unloading condition; this failure pattern is obviously different from uniaxial, triaxial compressive failure. It was validated by experiments that the ringlike failure occurred only under the unloading condition.(2) The real triaxial energy criteria (in the following) taking account of the influence of intermediate principal stress on energy release was preliminarily set up and validated. The influential coefficient of intermediate principal stress on energy release of limestone cylinders was obtained.(3) The unstable distribution of energy peak-value in thick wall of rock cylinders and whether the energy at peak-value point conforms to the energy failure criteria were judged. Based on the principles of minimum energy dissipation and Griffith strength theory, the ringlike axial failure mechanism was effectively discovered.(4) Based on the splitting fracturing characteristics of rock unloading failure and minimum energy dissipation characteristic of tensile failure, from the two viewpoints of stiffness and energy conditions, rock burst tendency of rock unloading failure was effectively illuminated(5) Based on the structural effect characteristics of rock failure, it was clarified the influence of intact loading structure of rock cylinder on the occurrence of ringlike failure. Based on RFPA2D, Producing location and formation condition of remote cracks in the middle part of rock was studied by numerical simulation. The producing location of remote cracks conforms to thedenotes the radius of circle roadways), which are in relatively consistent with the fracturing location of zonal disintegration.