| The length of newly excavated roadways in China's coal mines is about 12000 km / a,with a huge scale,ranking first in the world.With the continuous increase of mining depth,in order to ensure the long-term stability of roadway surrounding rock,more and more rock roadways are arranged in tight and hard rock strata with good integrity.Low drilling intensity,slow hole forming speed,poor blasting efficiency and large loss of machines,tools and materials are common problems in underground rock engineering construction of coal mine.Therefore,how to effectively break the rock has become one of the important problems to be solved in deep mining.In this thesis,ultrasonic vibration is introduced into rock fracture.Using the high-frequency characteristics of ultrasonic,red sandstone is selected as the test object.Using the comprehensive research method of indoor test,numerical simulation and theoretical analysis,the mechanical response characteristics of loaded rock,damage and fracture evolution process and the dynamic characteristics of "Ultrasonic vibration excitation-rock" system are systematically studied.The main research results are as follows:(1)The mechanical model of "simple harmonic excitation force-viscoelastic body" vibration system and the motion equation of rock micro element are established,the dynamic effect of rock under high-frequency vibration excitation is clarified,the significant spatial difference between displacement and acceleration of rock micro element is revealed,and the effectiveness and superiority of rock breaking under the compound action of "excitation force + static load force" of ultrasonic vibration are clarified;The mechanical model of rock subjected to concentrated and uniformly distributed vibration load is established,the evolution characteristics of stress components such as pull-down and shear under the combined action of high-frequency excitation force and static load are clarified,and the composite damage failure mechanism of rock "tension-shear-fatigue" is put forward.(2)The test shows that ultrasonic vibration excitation can effectively reduce the strength and deformation resistance of rock,and quantitatively characterize the weakening characteristics of cumulative excitation time on mechanical properties such as compressive strength and elastic modulus of rock;The three-stage progressive failure characteristics of rock "crack initiation crack propagation,upper end collapse and falling off cyclic intrusion failure" excited by fixed frequency ultrasonic vibration are obtained;The deformation characteristics of rock with the increase of excitation time,the increase of circumferential strain and the decrease of axial strain are mastered,and the rock fracture judgment method based on the change of strain rate is put forward;The quantitative relationship between different static forces and the Initial effective fracture depth of rock is obtained,and the variation characteristics of the dynamic reduction of the natural frequency of red sandstone with the excitation time are clarified.(3)The pseudo color enhancement technology and three-dimensional reconstruction technology are comprehensively used to extract the pore and fracture areas of rock,and the dynamic propagation characteristics of fractures in rock are defined.In the early stage of excitation,radial cracks are basically uniformly distributed on the upper surface of the rock.With the increase of excitation time,the cracks gradually expand along the radial and longitudinal direction and finally penetrate to form a fan-shaped fracture surface.The evolution process of upper-middle-lower steps of rock porosity excited by ultrasonic vibration is mastered,and the relationship between porosity increment and spatial location of rock is quantitatively characterized;The dynamic expansion law of pores with different sizes in rock is quantitatively analyzed.Based on nuclear magnetic resonance T2 spectrum,a fractal characterization method of rock pore evolution under ultrasonic vibration excitation is proposed.(4)Based on the principle of energy conservation,the expression of variable frequency and amplitude excitation force of ultrasonic vibration is obtained,the dynamic model of "ultrasonic vibration excitation rock" system considering the influence of static load force and rock damage degree is constructed,the analytical expressions of exciter and upper and lower surface displacement of rock in the loading and unloading stage of excitation force in a single cycle are obtained,and the critical failure criterion of rock under ultrasonic vibration excitation is given,The "Three-stage" progressive evolution of rock intrusion process of actuator under ultrasonic vibration and the law of rock intrusion depth increasing with the increase of static load,power,vibration frequency and damage degree are clarified;The concept of rock breaking energy efficiency excited by ultrasonic vibration is proposed,the expression of rock breaking energy efficiency in the stages undamaged,medium-term and late stage of rock failure is given,and the quantitative relationship of rock breaking energy efficiency with static load,power and vibration frequency is clarified.(5)The progressive evolution process of tension shear crack in loaded rock under confining pressure,the "V" shaped propagation characteristics of crack and its influence by the changes of vibration system parameters are clarified.The energy evolution characteristics of "elastic energy accumulation dissipative energy growth" of rock fracture with different sizes under ultrasonic vibration excitation are obtained,and the nonlinear size effect of rock failure is explored;Taking the intrusion depth,crushing area and cumulative crack number as indicators,the sensitivity of vibration parameters and confining pressure to rock breaking efficiency is revealed through four factor and four level orthogonal test,which provides a basis for the optimization of rock breaking process parameters excited by ultrasonic vibration.This thesis includes 139 figures,26 tables,and 151 references... |
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