| The structural plane of rock mass is a weak plane,which plays an important role in controlling the deformation and failure of rock mass.Based on the field investigation and harnessing engineering practice of Zhenzi dangerous rock mass in Nanchuan,Chongqing,referring to the mechanical parameters of limestone in limestone area,the deformation,failure modes and mechanical properties of fractured structural plane rock specimens with various geometric factors such as length,inclination and number are analyzed under 18 working conditions by means of indoor compression test and numerical simulation test under three-dimensional stress state.(1)The failure modes of specimens under different stress states are analyzed.Under unidirectional stress,brittle failure occurs,shear failure occurs in complete specimens,and longitudinal splitting failure occur in steep structural specimens.Fracture failure surface is controlled to a certain extent by fracture structure surface when fracture structure surface is long.Shear slip "smooth surface" appears when confining pressure is small under three-dimensional stress."Sawtooth" cross section appears in the middle of some specimens when confining pressure is high.(2)The stress-strain curve under unidirectional stress has obvious brittle failure characteristics.The stress-strain curves of various working conditions under confining pressure show a transition state from brittleness to plasticity and a plastic flow pattern.Strain hardening occurs at some working conditions when confining pressure increases sufficiently large.(3)Based on Mohr-Coulomb strength criterion,the range of internal friction angle and cohesion of shear strength parameters is obtained.(4)With the increase of confining pressure,the peak strength and residual strength of specimens increase.Peak strength deterioration coefficient and residual strength deterioration coefficient ? are introduced to characterize the degree of strength weakening caused by geometric factors of fracture discontinuities.(5)Based on Young's modulus characteristics,the influence of fracture geometry on deformation characteristics of specimens under different confining pressures is discussed.(6)The pre-failure strain and confining pressure of steep inclined structural planes show a positive growth trend.The mathematical expression of the relationship between strain and confining pressure before failure is obtained.Peak strain is greatly affected by crack structural plane.(7)The simulation test results of RFPA software are compared with the corresponding indoor test results,and the results are basically in agreement with each other.Observing and Analyzing the Failure Process Diagram of the Specimens to Obtain the Crack Propagation.There is a linear relationship between the expansion angle of single crack specimen and the inclination angle of structural plane.The longer the length of the structural plane,the later the extension line of the upper crack appears.Expansion lines are more likely to appear in a single fracture than in a double fracture.The acoustic emission characteristics of model specimens are studied.As the loading proceeds,the activity of AE becomes active gradually.The peak acoustic emission times of model specimens with steep inclined structural planes are larger.Under unidirectional stress,the first quiet period of acoustic emission occurs in the initial stage of loading.The duration of the first quiet period increases with the increase of inclination.The shorter the fracture structural plane is,the longer the duration of the first quiet period is.The value of the quiet point increases linearly with the increase of confining pressure under three-dimensional stress.The number of initial instantaneous acoustic emission increases linearly with the increase of confining pressure.The second quiet period of acoustic emission occurs in the residual deformation zone.Acoustic Emission Characteristic Map shows "double peaks","three peaks","thin and tall" and "short and fat" patterns. |
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