Rock Breaking Mechanism Of TBM Disc Cutter In Linear And Rotary Cutting Modes And Influencing Factors

The tunnel boring machine?TBM?uses a rotary cutter for excavation,and at the same time breaks the surrounding rock and tunneling in the tunnel,it can form the entire tunnel section at one time,which has obvious advantages in the construction of long tunnels.Disc cutters and cutter head are the key rock breaking tools of TBM,we need to reasonably predict the law of rock breaking force of them during rock cutting process,and study the rock breaking effect and influencing factors under different cutting modes,which is of great significance to understand the rock breaking mechanism and optimize the tunneling process.In this paper,a new prediction model of rock breaking force is proposed based on the rotary cutting mode of disc cutter,which complements the shortcomings of the previous prediction model in calculating the lateral rock breaking force.Furthermore,ANSYS/LS-DYNA is used to simulate the rock breaking process of the disc cutter in linear cutting and rotary cutting modes.The similarities and differences of rock breaking effects between the two cutting modes are compared,and the effects of penetration depth,cut spacing,and confining pressure ratio on rock breaking force and specific energy consumption of rock breaking are discussed.Finally,the numerical model of full-scale cutterhead driving process is established,the effect of TBM cutterhead rock breaking and the impact of cutterhead speed on the surrounding rock disturbance are analyzed.The main results are as follows:?1?The circular section of the disc cutter head of the constant section?CCS?is simplified to a straight section,and the process of the cutter intruding into the rock is assumed to be the vertical pressing motion of the cutter.Based on the above two points,a new prediction model of rock breaking force is proposed.Through error analysis with the test results,it is found that the calculation results of the vertical rock breaking force and rolling rock breaking force are relatively reliable.And the calculation results of the lateral rock breaking force are in accordance with the change rule with the penetration and the cut spacing,but slightly smaller than the test data.The reason may be that the lateral rock breaking force is to fully consider the cooperative rock breaking effect of adjacent hobs.The reason may be that the calculation formula of lateral rock breaking force does not consider the cooperative rock breaking effect of adjacent cutters.?2?During the linear cutting process,the vertical and rolling rock breaking forces increase with the ascending penetration.The growth rate of rolling rock breaking force is larger than that of vertical rock breaking force,and the maximum Mises stress in rock increases approximately linearly.For Colorado red granite,when the penetration is less than 4mm,the optimal cut spacing appears is around 65mm,with the increase of penetration,the cut spacing/penetration ratio?S/P?decreases from34.4 to 17.9.When the penetration is greater than 4mm,with the increase of penetration,the optimal cut spacing increases from 83.67mm to 115.78mm,and the S/P value gradually drops to around 15.When the penetration is 6.4mm and the cut spacing is 101.52mm,the minimum specific energy consumption of rock breaking is31.86 MJ.m^-3.?3?Compared with linear cutting,the vertical rock breaking force in rotary cutting mode decreases,the rolling rock breaking force increases,and the lateral rock breaking force increases significantly.The effect of penetration and cut spacing on rock breaking force in rotary cutting mode is basically the same as that in linear cutting mode.The difference is that the optimal cut spacing in rotary cutting mode is larger than that of linear cutting.When the penetration is less than 4mm,the minimum specific energy consumption of rock breaking in rotary cutting mode is less than that in linear cutting;when the penetration is greater than 4mm,the minimum specific energy consumption of rock breaking in rotary cutting mode is greater than that in linear cutting.?4?Under the confining pressure,during the rotary cutting of the hob,the vertical rock breaking force increases significantly,and the rolling rock breaking force decreases accordingly.As the confining pressure increases,this trend becomes more obvious.When the confining pressure ratio=0.5,the average vertical rock breaking force of Hwangdeung granite,Macheon granite,and Busan granite is increased by83.39%,50.78%,and 72.93%respectively than that there is no confining pressure;and the average rolling rock breaking force decreases by 26.19%,20.41%and 16.11%,respectively.As the confining pressure ratio increases,it becomes more difficult for the cutter to invade the rock,and the maximum Mises stress in the rock is transferred from both sides directly below the groove and gradually extends to the upper free surface.The rock breaking volume decreases with increasing confining pressure ratio,and the specific energy consumption of rock breaking increases with increasing confining pressure ratio.In addition,an interesting phenomenon is that the sensitivity of high-strength rock to confining pressure ratio is obviously higher than that of low-strength rock.The maximum specific energy consumption of hwangdeung granite,Macheon granite and Busan granite under confining pressure is 14.37%,10.06%and 7.86%higher than that without confining pressure.?5?Combined with the actual engineering case,the numerical simulation study of the TBM full-section excavation process was carried out.In the numerical modeling process,the influence of factors such as penetration,cut spacing and confining pressure were considered comprehensively.And the influence of rock failure form and the rate of tunneling on the range of the surrounding rock disturbance zone during the TBM full-face driving process was studied,the results show that as the TBM excavation rate increases,the range of the surrounding rock disturbance zone gradually decreases.The research results of this paper have certain theoretical reference value and practical guiding significance for the deep understanding of the law of rock breaking force of disc cutter and the optimization of tunneling construction process.