Optimization Research And Engineering Application Of Influencing Factors Of TBM Hob Rock Breaking Under High Ground Stress

With the development of tunnel engineering technology in China,tunnel engineering is no longer limited to mountain crossing tunnel engineering and urban subway engineering,but is developing towards deep sea.Long tunnel,subsea tunnel,deep rock tunnel and other key and difficult tunnels are playing a more and more important role.At this time,the TBM driving method in deep rock must consider various factors in the process of driving.At the same time,TBM cutter head and hob,as the key tools of rock breaking,are also the focus of TBM rock breaking efficiency.Based on the linear hob rock breaking prediction model,this paper puts forward a multi cutter rotary cutting rock breaking prediction model,which provides a suitable model for further study of TBM rock breaking influencing factors.In the hob rotation model,the influence of confining pressure,cutter spacing,penetration and hob rotation speed on rock breaking efficiency can be considered at the same time,which makes up for the deficiency of linear cutting model and linear cutting model.The main contents of this paper are as follows:（1）Because the TBM hob rock breaking test generally has a long period and high cost,the simulation of rock and soil cutting with the help of numerical simulation software is accepted by the majority of researchers.The current hob rock breaking linear cutting simulation software generally uses finite element simulation software and discrete element simulation software.Discrete element software has advantages in simulating the cracks,crack growth and internal damage of the rock.Without considering the cracks,crack propagation and internal damage,in order to better simulate the changes in the rolling force,rock volume and rock breaking effect during the rock breaking process of the hob,the finite element software is more suitable for simulating the rock breaking analysis process of the hob.（2）The establishment of the hob rock breaking model relies on the rocks selected by the Jinping II Hydropower Station project to belong to a higher-strength stratum,and the constitutive relationship of the rock model selects the Drucker-Prager（D-P）model.The hob model is simplified on the basis of Solid Works modeling.After the model is established,it is necessary to verify the consistency between the numerical model and the rock-breaking test.The average rolling force and the rock-breaking specific energy are selected as comparison indicators,and refer to the TBM rock-breaking test.The error analysis with the test results shows that the maximum error of the rock breaking average rolling force among the rock breaking test and numerical simulation results is 15.5%,and the maximum rock breaking average vertical force error is 13.8%.During the rock breaking process,the rolling force and the vertical force are in good agreement,which proves the correctness of the numerical model.（3）Based on the linear cutting rock breaking model,the influence of different confining pressure and different cutter spacing on the rock breaking process of hob is studied.The results show that the maximum effective stress increases linearly with the increase of confining pressure.However,the equivalent plastic strain will be restrained obviously with the increase of confining pressure.It is found that the rock breaking specific energy of hob rock breaking simulation is different under different confining pressures.The smaller the confining pressure is,the smaller the rock breaking specific energy is and the higher the rock breaking efficiency is.The results show that the specific energy of rock breaking decreases first and then increases when the cutter spacing is from 30mm to 90mm.There is an optimal cutter spacing with the highest rock breaking efficiency under different confining pressures.（4）On the basis of hob linear cutting simulation,a multi-hob rotary cutting model was established,and an orthogonal experiment with multiple influencing factors was established.These include:confining pressure,penetration,knife spacing and hob rotation speed.Arrange the simulation experiment of 4 factors and 4 levels,and use the orthogonal table ofL₁₆（4⁴）level as the orthogonal table.A comparative analysis of 16 combinations of rolling force,vertical force and rock breaking specific energy is carried out,and the degree of influence of each influencing factor on the rock breaking process of the hob and the sensitivity of each influencing factor to the rock breaking efficiency are obtained.The range analysis of the same comparison scheme shows that the sensitivity of different factors to the rock breaking efficiency of the hob is:cutter distance>revolution speed>penetration>confining pressure,which conforms to the results of the orthogonal experimental design analysis.（5）On the basis of linear cutting and rotary cutting,the numerical simulation of TBM full-section is carried out,and the TBM cutter head model is established with Solidworks and imported into the finite element analysis software.It provides an intuitive research method for studying the TBM hob tunneling process,mainly studying the rock breaking effect of TBM under different confining pressures.By comparing the Mises stress and PEEQ（equivalent plastic strain）under different confining pressures,it is found that as the confining pressure increases,the Mises stress gradually increases during the TBM rock breaking process;PEEQ（equivalent plastic strain）increases with the confining pressure.Large,there is a relatively decreasing trend.This working condition is also in line with the characteristics of the current deep and large tunnel engineering,and provides a certain theoretical model research basis for the tunnel engineering.