Study On Argillization Of Mudstone And Operational Parameters Of TBM During The Tunnelling Process

When the tunnel boring machine(TBM)penetrates into mudstone layer,the argillization effect will occur if the operational parameters are inappropriate.Furthermore,this phenomenon will induce the“mud cake”on the cutterhead.The clogging of cutter gives rise to the increase in cutterhead thrust by more than 20%and the abnormal wear of disc cutter.In addition,the frequent cutters change will increase the total cost obviously.Frankly,research on the rock breaking mechanism is a hot topic and difficult point in tunnel engineering.However,the understanding on this topic is rare now.In the present study,the argillization process of the mudstone was investigated from the macroscopic and mesoscopic perspectives under the thermal-hydraulic-mechanical coupling effect.The corresponding influencing factors were analyzed in the experiments.Furthermore,the effects of argillization on cutter wear and rock breaking efficiency of TBM were investigated.In the theory,cuter wear prediction models considering the argillization were proposed.After that,according to the numerical simulation,the mechanical parameters of the TBM hob rock breaking were optimized from the perspective of energy.Finally,according to the research results,the field data in the Nanqiaosi-Sports Park section of the Chongqing Rail Transit Circle Line were analyzed,corresponding suggestions were proposed.The work was supported by the National Natural Science Foundation’s“Research on the Macroscopic and Mesoscopic Fragmentation Mechanism of Jointed Rock Masses by the disc cutter and the TBM cutting efficiency”(51879016).The main works and results of this paper are as follows:(1)To reveal the argillization mechanism of mudstone by disc cutter,the cutter rotary indentation test machine and the miniature TBM rotatory cutting test machine were developed independently.Subsequently,the indoor tests were carried out on the mudstone samples.In the experiment,the temperature fields on the scaled cutter and tested rock surface were monitored through an infrared thermal imager,the argillization process of mudstone was observed.After the loading,the microstructures of the cutting grooves and the slacking mudstone were observed by stereomicroscope.According to the experimental result,the reason for the reduced cutting efficiency caused by argillization effect was explained.The harms of argillization effect were summarized,including the clogging of cutter and cutterhead,uneven wear and secondary wear of disc cutter,the high temperature of cutter and the rock.(2)The argillization mechanism of mudstone by disc cutter was reveal considering the thermal-hydraulic-mechanical coupling effect.In the cutter rotary indentation test,stereomicroscope was employed to observe the microstructures of the cutting grooves and slacking mudstone at different times.Considering the thermal-hydraulic-mechanical coupling effect,the argillization process of mudstone was divided into mechanical stage,the deterioration of mudstone microstructure and the formation of slacking mudstone stage and the adhesion stage.Specifically,in the mechanical stage,the rock was cut by mechanical action.In the deterioration of mudstone microstructure and the formation of slacking mudstone stage,water-weakening effects,thermal effect and mechanical activation induce the deterioration of mudstone and the formation of slacking mudstone.In the adhesion stage,the slacking mudstone was adhered to the disc cutter under the normal force.Subsequently,the crystal particles will crystallize,causing the“mud cake”.(3)The influences of the water addition and the rotational speed of cutterhead in the argillization process were analyzed,respectively.Thus the optimal optimum water addition and the rotational speed can be determined.Specifically,in the cutter rotary indentation test,the beneficial and unfavorable effects of water addition on the rock breaking process were pointed out firstly,including cooling,dust reduction,promoting the deterioration of the mudstone microstructure,and causing the clogging of cutter.In the miniature TBM rotatory cutting test,the macroscopic failure characteristics of the rock and the microstructure of the cutting grooves and the slacking mudstone under different rotational speeds were observed.Then the influence of the rotational speed on the rock breaking,the formation and adhesion characteristics of the slacking mudstone were analyzed.Finally,the optimal rotational speed of cutterhead was given.(4)The evolution of cutter wear considering argillization and the effect of water addition on cutter wear and rock breaking efficiency of TBM were studied.In the cutter rotary indentation test,the evolution of cutter wear under the condition of argillization was analyzed by observing the microstructures of the cutter under different loading times.Then the effects of argillization on the amount of wear and wear form were investigated.Based on the field penetration index,the effect of argillization TBM rock breaking efficiency was analyzed subsequently.The experimental results show that the cutter wear under the condition of argillization can be divided into mechanical wear stage,argillization wear stage and accelerated wear stage.The cutter waer was determined by the combined effects of mechanical action,adhesion of slacking mudstone,lubrication of water and secondary wear.The adhesion of slacking mudstone will cause the uneven wear of disc cutter,leading to the flat wear eventually.Argillization of mudstone will cause the clogging,thus reducing the cutting efficiency.(5)Based on previous studies,two cutter wear prediction models,which take the argillization effect into consideration,were proposed,named prediction model based on the"hybrid lubrication-cavity expansion"theory and prediction model based on the"contact slip-energy"theory.The former introduces elastohydrodynamic lubrication theory.It is believed that the cutter is in a mixed lubrication condition under the condition of argillization.Then the cavity expansion model was revised to determine the thickness of the mud layer.The stress on the cutter-rock contact surface was revised to calculate the normal and flat wear.The latter was proposed based on energy method by the previous scholars.In this model,the slip of the cutter,the work done by the rock chips and the starting torque of cutters were considered.By predicting the cutter wear in the test,the proposed models were verified.(6)Based on the discrete element program named PFC 3D,the miniature TBM rotatory cutting test was simulated.The energy in the rock breaking process was calculated.Furthermore,the cutterhead thrust,tip angle and tip width was optimized according to the energy evolution characteristics.In PFC 3D,the adhesive rolling resistance linear model is introduced to simulate the adhesion of mud on disc cutter.In the case of argillization,the consumed energy during the rock breaking process increases dramatically.The optimal cutterhead thrust can be obtained from the Colorado School of Mines model.The optimal tip angle and tip width are 40 deg and 13 mm,respectively.(7)The field data collected from a section of the Chongqing Rail Transit were analyzed.Especifically,the cutter wear was predicted by the proposed model in the present study.According to the results,it is recommended that the optimal cutterhead thrust Th=8294.6 k N,the optimal rotational speed of cutterhead N=2.8 rpm,the water addition in each circle is 0.5 m~3.The recommended values are similar with that of in engineering practice.