| The working performance of cutterhead,which is the direct tunnelling component of the full face rock tunnel boring machine(TBM),directly affects the efficiency and safety of construction.Due to the complex geology,such as crumbly strata,super hard rock and jointed rock,cutterhead bears large thrust,strong torque and impact loads in the tunnelling process.In addition,if the operating parameters are not properly controlled,the severe vibration,which could lead to the serious structural failure,would be caused in construction.Engineering practice showed that the consumption of cutterhead and cutter could be up to one-third of the total cost of TBM constructions.Therefore,it is of great significance to investigate the tunnelling loads and mechanical properties of the cutterhead.Firstly,based upon the study on the characteristics of rock material,a numerical simulation method for the tunnelling process of TBM cutterhead was developed and its feasibility was validated by the model experiment.The process of TBM tunnelling was considered as a problem of damage and failure in rock.By defining the constitutive equation,the damage law and the separation criteria,the mechanical behavior of rock in the tunnelling process was well described.The interaction between cutters and rock in the tunnelling process was described using the contact pair algorithm.And based on the ratio of kinetic energy and internal energy,the optimal solving strategy of the explicit simulation was given.Meanwhile,in order to solve the problems of time consuming and much repetitive operation in cutterhead modeling,a parametric modeling method for finite element analysis of TBM cutterhead was developed using the ANSYS Parametric Design Language(APDL),and the reliability of the modeling method was verified by the modal experiment of cutterhead.Secondly,a large number of numerical experiments were carried out using the tunnelling simulation model.And based on the simulation results,the spatial and temporal distribution of cutterhead loads was analyzed.Moreover,the effect of different parameters on cutterhead loads was discussed.According to the interaction between cutters and rock,the tunnelling loads on cutterhead and the rock-breaking forces on cutters were obtained.Then,the temporal distribution characteristics of the loads were studied from the perspectives of time-history responses,amplitudefrequency characteristics and statistical characteristics.Results reveal that the responses of the loads show some randomness,the thrust approximately obeys the normal distribution,while the torque,the normal and tangential force on cutters approximately obey the lognormal distribution.And in the space domain,the rock-breaking forces on cutters increase with the increase of cutters' installation radius.As for the action points of the normal resultant force on cutterhead,they are concentrated in the hard rock region when TBM tunnels through the inhomogeneous geology.Considering the uniaxial compressive strength(UCS)of rock,the penetration and the diameter of cutterhead as variables,respectively,the effect of the parameters of geology,operation,and structure on cutterhead loads was analyzed.Results reveal that the cutterhead loads are proportional to the UCS of rock,they also change with the penetration and the diameter of cutterhead following a power function.Additionally,by comparing with the in-situ data obtained from the Water Supply Project in the middle of Jilin Province,the simulation loads were validated and the relative errors were within the engineering permissible range.Thirdly,according to the loads got from tunnelling simulation,the strength properties of the cutterhead,which was used in the Water Supply Project in the middle of Jilin Province,was analyzed under the static extreme loads,the quasi-static random loads,and the dynamic loads,respectively.Under the extreme thrust and the unlocking torque,the strength of two cutterheads with different layout was analyzed.Based upon the distribution characteristics of rock-breaking forces on cutters,the failure probability of the cutterhead's strength was calculated using the Monte Carlo method.And the results were analyzed from the aspects of correlation and sensitivity.Results show that the forces on the normal cutters with the maximum installation radius have the most significant effects on the failure of the cutterhead's strength.As for the cutters,the strength failure mainly occurs in their shaft and holder.In addition,the transient dynamic analysis was performed on the cutterhead and its supporting system with the dynamic loads obtained from tunnelling simulation.And the strength properties of the cutterhead,the cutterhead support and the main beam were checked.Results show that strength failure would occur in the stiffened panels of the cutterhead.According to the simulation results,the structure of the cutterhead was optimized,and the optimized cutterhead has been successfully applied to the construction.Finally,in order to avoid the dynamic failure of cutterhead revealed in the strength analysis,the dynamic characteristics of cutterhead were studied from the perspectives of natural vibration characteristics and dynamic stability.Considering the interaction between the cutterhead and rock,the modal analysis was carried out.And the results reveal that the natural frequencies of the cutterhead's axial vibration modes increase with the increase of UCS and penetration.In addition,according to the characteristics of the system's responses to the disturbance,the dynamic stability of the cutterhead was analyzed.The method for determining the critical advancing speed which ensures the dynamic stability of the cutterhead was given.Results show that with the increase of UCS,the critical advancing speed of cutterhead decreases in the form of a logarithmic function.To give a greater space for adjusting the operating parameters,the curve of the critical advancing speed should be moved up by optimizing the cutterhead's structure in design.Moreover,to avoid the generation of large amplitude vibration in TBM tunnelling,the advancing speed should be controlled in the region below the critical curve.In summary,a direct numerical simulation method for the tunnelling process of TBM cutterhead was proposed in the paper.The temporal and spatial distribution characteristics of cutterhead loads and cutter forces were analyzed.And the effect of the parameters of geology,operation,and structure on cutterhead loads were discussed.In addition,the structural performance of the cutterhead was evaluated.The analysis methods of the cutterhead's strength and dynamic stability were given.The proposed methods provide effective means for the study of the mechanical properties of TBM cutterhead.The results can provide reference for the design of load balance,geological adaptability and dynamic stability of the cutterhead,and they can also provide guidance for the real-time control of the operating parameters in TBM tunnelling. |
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