Prediction Of Disc Cutter Failures During Shield Tunnelling In Soil-rock Varied Ground

This study was undertaken to address disc cutter failure issues during shield tunnelling in soil-rock varied ground,which includes mixed-face ground and soft-hard alternate ground.This study intended to i)analyse the characteristics,influence factors,and classification of disc cutter failures;ii)predict the normal continuous wear of a disc cutter;iii)address the correlation between the friction energy and abrasive mass for lateral continuous wear;and iv)predict the side force on the lateral side of the cutter ring.In order to investigate these issues,a theoretical analysis,numerical simulation,and verification in the field were conducted.The disc cutter failures in soil-rock varied ground were reclassified.A new prediction model for the normal continuous wear was proposed by calculating the friction energy consumed in the cutting process.The results of abrasion tests were used to determine the correlation between the friction energy and abrasion mass.Then,a prediction model for the lateral continuous wear was proposed.The circular cutting theory was used to analyse the mechanical condition on the lateral side of the cutter ring.A method for calculating the side force on the disc cutter was deduced.The concluding remarks of this study are summarised as follows.(1)Disc cutter failures were reclassified based on mechanism analysis.According to the occurrence position and failure type,a particle model that included the cutter ring,cutter body,and rock sample was built to analyse the failure mechanism.The simulation results showed that i)the normal continuous wear was a material abrasive phenomenon that occurred on the normal side of the cutter ring;ii)the normal brittle failure was caused by the crushing process between the normal side of the cutter ring and the rock sample;iii)the lateral continuous wear was a material abrasion process occurring on the lateral side of the cutter ring;and iv)the lateral brittle failure was correlated to the imbalance between the side forces on the lateral sides of the cutter ring.(2)A prediction model for the normal continuous wear was proposed.According to the analysis of the friction process in mixed-face ground,the slide friction at the contact surface between the cutter ring and rock sample was supposed as the main factor for the normal continuous wear.Based on the assumption that the contact stress was uniformly distributed,a calculation method for the normal contact pressure was proposed.By analysing the moving process of the cutterhead,the influence of impact loading was determined.The friction energy consumed during the cutting process could be calculated using a theoretical analysis.Based on the assumption that the abrasion volume of material was consistent,a statistical method was proposed to convert all the wear contents into the same form.According to the field cases,the correlation between the friction energy and wear content was determined.Then,a prediction model for the normal continuous wear was proposed.(3)A prediction model for the lateral continuous wear was proposed.According to the analysis of the cutting process in loose ground,the cutting groove under the loose ground condition was induced by the lateral contact between the cutter ring and plastic ground.The self-sharpened phenomenon of lateral continuous wear was caused by the abrasive minerals in the loose ground.The cavity expansion theory was used to explain the deformation process under the loose ground condition.The deformation induced by the cutting process was concluded to be cavity expansion,similar cavity expansion,and uniform deformation.With the normal solution of the cavity expansion theory and the interpolation method,the friction force on the lateral side of the cutter ring and corresponding friction energy could be calculated.The results of an abrasion test were used to regress the correlation between the friction energy and abrasion mass.Finally,a prediction model for the lateral continuous wear was proposed.(4)A new method for the mechanical analysis of lateral brittle failure was proposed.According to the field observations under the fully weathered ground condition,the lateral brittle failure was more likely to be found in the central region of the cutterhead.Using the circular cutting theory,the variation of the lateral contact behaviour was found to be consistent with the distribution of the lateral brittle failure.Additional results showed that i)when the spacing radius was increases,the lateral contact area decreased;ii)with an increase in the penetration depth,the lateral contact area increased but the increase rate slows down;and iii)the increase in the rotation speed of the cutterhead aggregates the impact loading.A numerical model was built to simulate the mechanical status of the cutter ring during the circular cutting process.The impact effect index was determined using a regression analysis.Finally,a new calculation method for the side force was proposed to explain the lateral brittle failure.(5)Research achievements were verified in field case studies.Two case studies at the Xie-Zhong section of Guangzhou Metro Line 7 and the Ji-Ming section of the Sui-Guan-Shen intercity rail were used to verify the research achievements.Based on the Guangzhou case,the characteristics of normal continues wear and lateral brittle failure were observed.The wear content during the normal continuous wear and the side force on the lateral side of the cutter ring were predicted and then verified by field observations.In the Shenzhen case,the characteristics of the lateral continuous wear were analysed.The effectiveness of the prediction model for the lateral continuous wear was confirmed.