| How to improve the efficiency of mechanical rock-breaking in hard-rock formations under complex stress conditions is one of the challenges of the drilling method of well-drilling technology.As the main consumption component of the shaft boring machine,the inserted teeth hob has shortcomings such as single tooth shape and poor crushing effect of hard rock.In this thesis,the idea of using a combination of and conical teeth in a inserted teeth hob to break rock was presented.Combined with CT test,laboratory test,numerical simulation and other methods,the rock breaking law of the spherical-conical-tooth collaborative intrusion of the hob in the high ground stress environment was studied.Firstly,for the differences in characteristics of local crushing of rocks under the action of spherical and conical inserted teeth,seven kinds of rock samples including sedimentary rocks,metamorphic rocks and igneous rocks were taken as the research objects.The relationship between brittleness index and load stability and rock breaking efficiency parameters in the process of inserted teeth intrusion was analyzed by intrusion rock breaking test of spherical and conical inserted teeth.Combined with the CT imaging technology,the influence of dense cores intruded by spherical or conical single teeth into different types of rocks on the crack extension process was analysed.The microscopic morphology and material composition of the dense cores were further analyzed by means of scanning electron microscopy(SEM)and X-ray diffraction analysis(XRD).The 3D contour scanner was used to reconstruct the rock surface after failure,and the change process of the fracture angle was described.The results show that the brittleness index of rocks under the action of conical teeth is lower than that of spherical teeth,and the particle size of rock fragments formed by their intrusion tends to be larger than that of spherical teeth.The load fluctuation of conical teeth during intrusion is greater than that of spherical teeth,which is favourable to rock breaking but also more prone to wear than spherical teeth.As the brittleness index increases,there is a linear decreasing trend in the volume and surface area of cracks induced in spherical teeth,and the opposite is true for conical teeth;And the cracks caused by the intrusion of the spherical teeth tend to extend axially to the depth,while the cracks of the conical teeth tend to extend radially to the rock surface.The intrusion of spherical and conical teeth will form dense cores in the rock,the location of the dense cores formed by spherical teeth is located below the intrusion point in the shape of an ellipsoid,while the dense cores formed by the intrusion of conical teeth are in the form of a ring or cake around the conical teeth,and their compositions are similar to those of the corresponding rock samples.The fracture angle formed by the intrusion of spherical and conical inserted teeth into different kinds of rocks is basically between 126～161°,but with the growth of the rock compression and tension ratio shows a tendency of decreasing and then increasing.Then,a discrete element model of real rock samples based on the GBM(Grain-Based Model)unit was established to simulate the crack extension process of rock samples under spherical and conical inserted teeth intrusion,and to reveal the particle crushing process in the rock breaking process of inserted teeth intrusion.And in-situ observation and analysis of the whole process of spherical and conical single/double inserted teeth intrusion rock breaking in stressful environments using a CT scan based rock breaking test system.The results show that the cracks within the dense core are mainly produced by the rupture of mineral crystals,and the percentage of cracks in each mineral fraction is similar to that of the rock samples themselves,and the growth rate of the number of cracks under the intrusion of the spherical teeth gradually slows down,while that of the conical teeth gradually accelerates.Based on the results of in-situ real-time CT tests,the mechanisms of dense core and crack extension within the rock during loading and unloading of the double-inserted teeth are revealed.During the intrusion of the double inserted teeth into the rock there is an "X" shaped crack between the double teeth.During the loading phase a disc crack is formed below the dense core of the spherical teeth and a lateral crack is formed on the side of the dense core of the conical teeth,and during the unloading phase a lamellar block is formed in the tensile stress zone between the double teeth.The disc cracks below the double spherical teeth extend through each other to the surface,the lateral cracks on the side of the double conical teeth extend to the surface,and during intrusion of the spherical-conical double teeth,the loading on the side of the spherical teeth is greater,and in addition to lateral disc cracks there are also conical Hertz cracks produced.Finally,based on the self-developed intrusion breaking equipment with high stress(0～60MPa),large specimen(Φ50 mm×h100 mm),and multi-tooth arrangement(double teeth,multitooth spacing),an experimental study was carried out to investigate the change rule of load stability and breaking efficiency of the spherical and conical teeth breaking process under the breaking parameters(intrusion velocity and depth)and stress environment(axial pressure and confining pressure).The results show that the increase of intrusion velocity and depth will lead to the increase of brittleness index,fluctuation strength and specific energy consumption of spherical and conical single inserted tooth,while the fluctuation frequency and average fragment size appeared to be reduced,and the increase of intrusion depth is conducive to the improvement of the efficiency of the double inserted teeth in breaking rock.The influence of stress environment on the effect of rock breakage is greater than the shape of the setting teeth,under the influence of deviatoric stress,the rock breakage evaluation indexes are symmetrical or nearly symmetrical distribution with the axis of the confining pressure of 10 MPa.The highest rock breaking efficiency was achieved at a principal stress difference of 5 MPa for a single tooth,and at 0 MPa for double teeth.The combined use of double teeth can improve the rock breaking influence range of each single tooth.Judging from the perspective of specific energy consumption,the best pitch of double spherical teeth is 1.5～2.5 times the tooth diameter,the best pitch of spherical-conical double teeth is 1.5～3.5 times the tooth diameter,and the best pitch of double conical teeth is 1.0～2.0 times the tooth diameter.Based on the intrusion rock breaking mechanism of spherical and conical inserted teeth,this thesis studies the rock breaking law of spherical and conical single/double inserted teeth under different rock breaking parameters and stress environments,and reveals the synergistic rock breaking mechanism of different-shaped double inserted teeth.It can provide theoretical guidance for the development of high-efficiency and low-energy hard rock breaking tools,which is of great significance for improving deep well drilling speed,reducing drilling construction cost and expanding the application range of drilling method.There are 120 figures,29 tables and 126 references in this dissertation. |
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