Study On Splitting Mechanism And Rock Breaking Optimization Of Intact Hard Rock

Rock breaking by drilling splitting method belongs to the category of non-blasting static rock breaking.It uses the characteristics that the tensile strength of rock is far less than the compressive strength.By applying the splitting force inside the borehole,the rock produces tensile cracks to achieve the purpose of rock breaking.It has the advantages of no flying stone,no dust and no vibration.It is widely used in many engineering sites restricted by drilling and blasting methods.However,the rock breaking mechanism and optimization of this method are still worthy of study.In this paper,theoretical analysis,laboratory test and numerical simulation are used to study the splitting mechanism and rock breaking optimization of intact hard rock.In terms of theoretical analysis,the mechanical model of splitting rock breaking is generalized,and the specific analytical expressions of the internal stress of the rock under the splitting force in the drilling hole under the rectangular and polar coordinates are derived by using the complex variable function theory.The correctness of the stress analytical solution of splitting rock breaking is verified by numerical means.Based on the derived stress analytical solution,the hole-edge stress and crack initiation of rock under splitting force are theoretically analyzed.In the aspect of laboratory test,the physical and mechanical parameters of rock are measured firstly,and then the laboratory test of splitting rock breaking is carried out.The research contents include whether the pre-cutting groove is set or not,the direction of the pre-cutting groove,the influence of the length of the pre-cutting groove on the rock breaking effect and the influence of the pre-cutting groove on the splitting force.The test results show that the pre-cutting groove can effectively control the crack initiation,inhibit the secondary crack and guide the crack to expand along the direction of the groove.The directional control of the pre-cutting chute is poor,and the pre-cutting straight groove can achieve better rock breaking effect.The longer the pre-cutting length is,the stronger the directional control effect on the rock fracture surface is.The variation curve of splitting force can be divided into three stages: energy storage preparation stage,crack propagation stage and instantaneous failure stage.In the aspect of numerical simulation,firstly,the guiding mechanism of pre-notch on the fracture surface is studied,focusing on the analysis of rock stress distribution,principal stress vector and evolution of tensile failure zone under splitting force.The results show that the pre-notch significantly changes the stress distribution of the orifice,and there is obvious stress concentration at the end of the pre-notch.The tensile stress at the end of the pre-cutting groove is always perpendicular to the cutting direction.The existence of pre-cutting groove also makes the tensile failure zone more concentrated and more continuous at the end of the cutting groove.Secondly,aiming at the problem of multi-hole splitting,the two-hole model is analyzed as a typical research object.The results show that there is a significant stress superposition between the holes when the splitting force is applied at the same time.The cracks between the two holes start at the notch between the holes,and then expand to the midpoint of the two holes along the line connecting the end of the notch,and finally form a macroscopic crack through the two holes.With the increase of borehole spacing,the minimum splitting force required for the connection of the tensile failure zone between holes gradually increases,and with the increase of the length of the grooving,the minimum splitting force required gradually decreases.