Study On The Optimal Penetration And Cutter Spacing Of Rock Breaking By Hob Considering Bedding Angle And Confining Pressure

With the leapfrog improvement of construction level of China,accelerating the construction of urban underground space,railways,and highways has become a necessary choice for urban development in the new era.Tunnel boring machine(TBM)is widely used in large-scale construction projects due to its fast,high quality,and safety.However,how to adjust the technical parameters and configuration of the hob according to different geological conditions(especially in the face of rock stratum defects and complex ground stress environment),so as to improve the working efficiency of the TMB heading machine has become a problem to be solved by the construction units.Hence,it is necessary to explore the mechanical response of rock with directional bedding structure under different confining pressures and the corresponding optimal rock cutting parameters.In this paper,the layered granite in a mining area in Lingshi County of Shanxi Province is selected as the research object.The macro and micro mechanical properties of rock under different bedding angles and confining pressures are obtained by using rock mechanics equipment,and the mechanical properties and weakened mechanism of rock under corresponding working conditions are obtained.The rock mechanical parameters obtained from the test are introduced into the established rock cutting finite element simulation model and its reliability is verified.On this basis,the finite element simulation software Abaqus is used to investigate the influence of penetration degree and hob spacing on the working efficiency of TMB under different working conditions.Based on the above analysis,the dynamic rock-machine interaction mechanism and the optimal single and double hobbing rock breaking parameters are obtained.The main work of the paper is as follows:(1)The mineral compositions and material properties of layered granite are obtained by a series of physical and chemical testing methods,rock layer model and hob model are preliminarily established by Abaqus,and the mechanical properties of layered rock are summarized by investigating the influence of hob rock breaking theory and confining pressure conditions,through a combination of domestic and foreign literature and field investigations.(2)The triaxial universal tester,microscopic computer tomography(MCT),and 3D laser scanning were utilized to obtain the peak strength,fracture surface morphology/roughness,and micro pore/crack damage structure of specimens subjected to different confining pressures and stratification angles.Tensile strength and fracture toughness of specimens with different bedding angles were obtained by uniaxial compression tester.From the test results,the weakening mechanism of rock from the angle of confining pressure and bedding is put forward,and the guiding opinions for rock breaking by hob are put forward.The mechanical properties of rock are greatly influenced by confining pressure and bedding angle,as shown by the results.At the same bedding angle,an increase in confining pressure leads to an increase in peak strength,a change in failure modes from complex to simple,and an increase in specimen roughness.Among the tested bedding angles,the strength and fracture roughness of specimens are the lowest for those with a 30° bedding angle,while specimens with a 90°bedding angle exhibit the highest strength and fracture roughness.Additionally,the tensile strength and fracture toughness of the specimen are the minimum when the bedding angle is 30°,and the maximum when the bedding angle is 90°.(3)The rock model is corrected by using Abaqus software and rock mechanical parameters,and single and double hobs are established for rock breaking under different bedding angles and confining pressures.The influence of confining pressure and bedding angle on rock breaking with single and double hobs is mainly discussed.Optimum rock breaking angle,roll-in degree of single hob,and rock breaking angle with double hobs and optimum spacing between two hobs are selected.The results show that the efficiency and energy loss of rock breaking by single and double hobs are significantly affected by the confining pressure and bedding angle conditions.The highest rock breaking efficiency and lowest specific energy are achieved when the bedding angle is30° under identical confining pressure conditions.For single hob,6 mm penetration has good rock breaking effect when confining pressure is 0 MPa and10 MPa,while 10 mm penetration has good rock breaking effect when confining pressure is 20 MPa.For double hobs,with the increase of spacing between hobs(20-70 mm)under the same confining pressure,the rolling force increases,the amount of rock crushing increases and the specific energy decreases.The recommended optimum spacing between knives under the three confining pressures is 70 mm.