| Shield tunnelling in mixed-face grounds（MFG）could lead to dynamic loads on cutters and cutterhead due to the heterogeneity and changing of the geological conditions at the working face and along the tunnelling axis,adversely influencing the safety of the cutting system and working face stability.Therefore,it becomes an essential issue to reveal the dynamic interaction between the shield cutting system and the complex ground conditions and the corresponding influence on the shield machine and the ground.In addition,the shield tunnelling-induced vibration is closely related to the geological properties of the working face.Based on this fact,establishing a method to recognize the working face conditions helps improve shield tunnelling safety and is significant for scientific research and engineering practice.The main work and innovations of the present thesis are as follows:（1）The time-variant properties of cutter force during cutting soil-rock interface（SRI）was studied by cutter linear cutting laboratory test and 3D finite element method with the strain-induced failure constitutive model.On this basis,the time-dependent equivalent strength of the SRI and a method to determine the time-varying cutter force during cutting SRI were proposed.The results showed that when the penetration p and cutting speed vc remained unchanged,the greater the rock UCS,the greater the peak load with a higher load growth rate（LGR）and fluctuation.The penetration p is positively related to the peak load and the time duration to reach the peak.Therefore,its impact on LGR needs to be specifically analyzed.With p and the rock UCS remaining constant,the peak forces under different vc are basically the same;that is,LGR increases with vc.From the perspective of cutter protection,the control envelope of vc and p was determined according to the critical LGR and peak force.（2）The vibration characteristics of the shield machine during cutting MFG and its relationship with the working face conditions were studied by field monitoring and theoretical analysis.It was proved that the time-domain and time-frequency characteristics of shield vibration were closely related to the rock-breaking mechanism.The period of shield vibration is consistent with the rotation period of the cutter head,and a specific vibration waveform will be generated by the particular disc cutter group cutting the SRI.The serial impact signals of millisecond-scaled contained in the waveform reveal the mechanism of the stepped rock-breaking process.A multi-body dynamic model of the shield cutting system was established to analyze the inherent relationship between the shield vibration and rock UCS,p,vc and the rock-breaking process by multi-cutters.It was found that the vibration characteristics of the cutting system were directly related to the geological properties of the working face,and it was more sensitive to ground changes than conventional excavating parameters.In the homogeneous ground,shield vibration is small and steady,while in MFG,a violent vibration with a large amplitude will occur.This is the theoretical foundation for the working face identification method based on shield vibration.（3）A ground identification method for the working face was established based on the 1D time series and 2D time-frequency characteristics of shield vibration.The accuracy of the recurrent neural network（RNN）model based on instantaneous frequency transformation of 1D time series can reach more than 80%.The convergency and accuracy of the convolutional neural network（CNN）models based on 2D time-frequency diagrams are better than RNN.Among the four CNN models,Res Net-18performs best in this issue and can achieve high efficiency and accuracy of feedback.When the feedback period is 1-second,the accuracy can reach 96.42%.Parametric analysis shows that the sample duration significantly influences the model performance.When the sample duration approximately equals the rotation period of the cutter head,the performance of the RNN models and the CNN models can become the best.The proposed shield vibration-based method realizes a real-time recognization of the working face conditions without affecting the normal tunnelling process and provides a reference for optimizing shield parameters.（4）Using field monitoring and laboratory model tests,the shield cutting-induced ground vibration and its influence on the stability and arching effect of the work face were studied.Laboratory model tests showed that the CIV increased the instability zone in the loose sand.With the same unloading condition,the top width of wedge Lwt increased by about 5.75%when considering the influence of CIV（Aa=0.2g,f=10Hz）.In contrast,CIV exerted a more significant effect on the dense sand,with Lwt increasing by about 35.66%.Under static conditions,a self-stable arch could occur in dense sand,while the long-time self-stable arch was hard to form in case of considering CIV.This is because the sand particles were acted by the additional inertial force caused by CIV and fell gradually from the arch,which would result in a progressive failure and finally a sudden collapse of the arch.The results also showed that the CIV had little influence on the limit supporting force σs,lim of the loose sand,which stabilized at about 0.075γD.In contrast,the influence of CIV on σs,lim in dense sand was more remarkable,which was about 0.08～0.09γD under static conditions and increased up to 0.15～0.20γD under dynamic conditions.（5）The development law of loosening zone of working face in homogeneous sand and MFG under CIV was revealed by discrete element modelling and ellipsoid theory.The results showed that the loosening zone and σs,lim in MFG were smaller than those in homogeneous sand since,in MFG,the collapse only occurred at the upper part of soft ground,and the lower rock part could provide better arch support.Besides,the loosening zone and σs,lim increase with CIV,and the increasing degree is positively correlated with CIV amplitude,which is verified mutually with the laboratory test results.When CIV amplitude increases from 0.5mm/s to 3mm/s, σs,lim increases from less than 0.2γD to 0.6～0.7γD.Since shield tunnelling in MFG generates significant CIV,which is harmful to the tunnel face stability,it is suggested that the CIV should be carefully controlled by optimizing the cutter configuration and cutting parameters in the tunnelling to reduce the disturbance of CIV on the ground. |
