| The rock stress environment of underground chamber and tunnel engineering is complex.Most rock is in a high stress state for a long time and is often affected by cyclic disturbances of surrounding engineering such as blasting stress wave,mining and tunneling,vibration of large mechanical equipment,mechanical drilling and so on.The stress field is redistributed,and the deformation and damage process of rock is changed.Under high stress,rock may induce various geological disasters by cyclic disturbance load.Therefore,it is of great significance to explore the changes of rock mechanical parameters and reveal the damage and failure evolution law of rock under cyclic disturbance load for ensuring the smooth construction and safe operation of underground chamber and tunnel engineering.In this paper,the influence of various parameters of cyclic disturbance load on the fatigue damage of rock is studied by using the self-made new multifunctional impact disturbance testing system of surrounding rock.The cyclic disturbance load tests of rock specimens under different static confining pressures and different dynamic confining pressures are carried out,and the confining pressure effect of the rock specimens damage evolution law is analyzed.The factors affecting the failure of the hole defect specimen are analyzed by the time-varying mechanics theory,and the biaxial equal pressure cyclic disturbance loading test is carried out on the hole defect specimen.The strain of the specimen is collected by the dynamic strain test system,and the whole process of specimen failure is recorded by high-speed camera.The biaxial equal pressure state of the hole defect specimen under the cyclic disturbance load is reproduce by using FLAC3 D,and the influence of the radius and the amplitude of the cyclic disturbance load on the specimen failure is analyzed.The main research contents of this paper are as follows:(1)According to the principle of the combination of static loading and cyclic disturbance loading,a new multi-functional impact disturbance testing system of surrounding rock is developed,and the structure and function of the testing system are introduced.The functions of the testing system were tested;the feasibility of the testing system is verified by gypsum specimens,which proves that the testing system is simple to operate,having many controllable variables,and the experimental data is true and reliable.The testing system can carry out experimental research on 300 mm × 600 mm × 600 mm coal rock specimens and rock-like specimens.The device has been granted an invention patent.(2)The cyclic disturbance loading tests of rock with disturbance amplitude ratio of 20 %and average stress ratio of 80 %,85 % and 90 % are carried out;the cyclic disturbance loading tests of rock with average stress ratio of 85 % and disturbance amplitude ratio of 15 %,20 %and 25 % are carried out.The damage constitutive model is introduced,and the effects of different average stresses and different amplitude on the rock fatigue damage are analyzed.The influence of disturbance load waveform and frequency on rock damage and failure is analyzed theoretically.When the stress level of cyclic disturbance load is lower than the threshold,the rock will not be destroyed,and the elastic modulus has a strengthening effect.The influence of rock specimen compaction degree and grain size on the strengthening effect of elastic modulus is analyzed.With the average stress increasing or disturbance amplitude increasing,the cycles times in the stable development stage of the specimen decreases significantly,the change rate of damage variable increasing,and the strain and damage amount of each cycle increase.When the upper limit stress exceeds the uniaxial compressive strength of rock,the increase of average stress and disturbance amplitude has a more significant effect on the cycle times of rock failure.When the upper limit stress is the same but the average stress and the disturbance amplitude are different,the influence of the average stress on the rock failure is greater than that of the disturbance load amplitude.(3)Rock-like material specimens are selected to carry out the cyclic disturbance test under the static confining pressure of 0 MPa,2 MPa,4 MPa,6 MPa and the dynamic disturbance confining pressure upper limit stress of 0 MPa,2 MPa,4 MPa,6 MPa.The strength,deformation characteristics and stress-strain curve variation of the gypsum specimen under the corresponding confining pressure were obtained.A variety of methods for calculating damage variables are introduced.Based on the analysis methods such as the inclination degree of hysteresis loop,the maximum strain at the beginning and end of cyclic disturbance loading,and the development law of residual strain,the evolution law of damage variables of specimens under various confining pressures is studied.The difference of damage variables of specimens under static confining pressure and dynamic disturbance confining pressure is compared,and the relevant methods are modified by Weibull statistical distribution function.The damage and failure mechanism of rock under cyclic disturbance load is expounded.The variation law of the failure mode under each confining pressure is analyzed.(4)The elastic-plastic time-varying solution of the biaxial equal pressure hole defect specimen is analyzed by using the time-varying mechanics theory,and the radial displacement time-varying solution of the biaxial equal pressure hole defect specimen is obtained.The factors affecting the specimen failure are analyzed,and the essential reason of rock failure is explained.The biaxial equal pressure cyclic disturbance loading test of different disturbance load average stress was carried out for the hole defect gypsum specimen,and influence of different disturbance load average stress on biaxial equal pressure hole defect specimen strain,fatigue life and damage under were obtained.FLAC3 D is used to numerically calculate the biaxial equal pressure cyclic disturbance loading on the hole defect specimen,and the influence of the hole defect radius and the cyclic disturbance load amplitude on the shear stress and displacement of the specimen is analyzed. |
