Research On The Law Of Rock Fragmentation With Inserted Tooth Hob Under Complicated Conditions In Deep Shafts

The construction of deep shaft is the first challenge in the development of deep ground resources and underground space.In order to guide the efficient mechanized rock breaking in deep shaft,the law of rock fragmentation using inserted tooth cutter under complicated conditions in deep shaft was studied by combining theoretical analysis,physical test and numerical simulation.Firstly,the working condition characteristics of mechanized rock breaking in deep shaft was analyzed.Combined with the characteristics of mechanized rock breaking in deep shaft,a set of CT scan based single inserted tooth crushing test bench for high stress conditions was developed for the first time.The apparatus was used to conduct rock indentation tests on granite and sandstone rock under different stress conditions(0MPa?20MPa),different displacement rates(0.1mm/min?0.8mm/min),different loading rates(0.05k N/s?0.2k N/s),and different tooth shapes(conical,spherical).It is found that the penetration depth vs.thrusting force curves exhibited several times of sudden drop fluctuation in the crushing process.The breaking surface of rock samples showed a chiseled pit and some crushed rocks.When the fluctuation frequency of force is smaller and the plunge amplitude of the drop is larger,the fracture brittleness of rock breaking is greater.The thrusting force of granite rock crushing test under the action of conical inserted tooth showed higher fluctuation frequency and smaller fluctuation amplitude than that under the action of spherical inserted tooth.With the increase of intrusion rate,the fluctuation frequency of thrusting force decreased.However,the average value of thrusting force in sandstone crushing test decreased first and then increased with the increase of intrusion rate.Under the conditions of no initial pressure,the rock samples all showed the integral splitting failure patterns,which induced by the propagation of vertical cracks.The formation direction of larger exfoliated fragment was approximately perpendicular to the crack direction.However,under the conditions of initial pressure,it is found that the initial pressure has a certain inhibitory effect on crack propagation.Confining pressure will restrain the propagation of vertical and radial cracks,while axial pressure will restrain the propagation of lateral cracks.The distribution of rock fragment removed from the crushing surface under triaxial initial pressure is more uniform than that under single confining pressure.Secondly,the in situ real-time CT scan of sandstone crushing was carried out to obtain the development state of crack propagation and crushed zone in stages.It was found that the cracks of crushed specimens were cross-shaped when using conical tooth,but the cracks of crushed specimens were triangular when using the spherical tooth.The crushed zone induced by spherical tooth were roughly teardrop-shaped,and the crushed zone induced by conical tooth were more in the range of both sides of the tooth.The obtained 3D reconstructed images visually revealed the interaction process between rock and inserted tooth cutter,and the mechanism of the formation of crushed zone during fragmentation.Then,the PFC software was used to simulate the indentation process of granite and sandstone rock to determine the effectiveness of this numerical model in simulating the rock crushing process.Based on the movement law of inserted tooth hob and the complex conditions in deep shafts,the investigations were carried to study the influences of breaking mode,initial pressure and joint characteristics on specific energy consumption of rock breaking and the fluctuation of crushing force.The results show that there is a critical value in the spacing between adjacent teeth,which makes the specific energy consumption and load fluctuation of inserted tooth cutter reach an extreme value.The rolling cutting with forward sliding are easy to produce lateral cracks.The lateral cracks will extend to the free surface of rocks to form rock chippings,which will affects the intrusion and crushing effect of next inserted tooth,while the backward sliding of the hob will cause the formation of crushed rocks after the chisel pit.When the ratio of initial stress to UCS reaches 0.8,the specific energy consumption decreases significantly,which shows that the high confining pressure will promote the efficiency of rock fragmentation.The analysis of discontinuous joints shows that the discontinuity ratio of joints has a great influence on the propagation of vertical cracks,which will be truncated when the cracks are expanded to the joints.Meanwhile,wing cracks easily appear at the tip of the joints,and the azimuthal distribution of microscopic shear cracks is greatly influenced by the joints.The maximum crushing force of rock cutting with continuous joints increased with the increase of the spacing of joints.The propagation depth of vertical cracks decreased with the decrease of dip angle of joints.Finally,the numerical rock models with different indentation hardness,fracture brittleness and fracture toughness were obtained by changing the strength coefficient in the micro parameters based on the calibrated granite and sandstone original micro parameters and the variation law between the macro parameters of rock samples and the micro parameters of numerical models.The rock breaking analysis of the single-ring inserted tooth hob is carried out based on those numerical rock samples.The results showed that the average value of the normal force of rolling rock cutting increased with the increase of the microscopic strength coefficient,and the vibration response of rolling cutting force and normal force is consistent.The rock failure is mainly caused by tensile failure in rock fragmentation,and the ratio of the number of micro tensile cracks to shear cracks increased with the increase of microscopic strength coefficient.By comprehensive analysis of lithology index and rock breaking index,energy consumption SE is found to increase with the increase of UCS,increase with the increase of brittleness B₅.Dimensionless energy consumption SE/UCS and brittleness B₂ and fracture toughness K_IIC are positively correlated.The research content of this dissertation considers the influence of several factors on the rock breaking behaviors of inserted tooth hob in the complicated environment of deep shafts,which has certain theoretical significance and practical reference value for realizing efficient rock breaking in the complicated environment of deep shafts.There are 154 figures,40 tables and 130 references in this dissertation.