Research On Shield Cutter Optimization And Tunnelling Parameter Prediction In Cobble Stratum

The shield method is widely used in the construction of underpass tunnels for its advantages of safety,stability,low disturbance to the surrounding environment and freedom from climatic and environmental conditions.Shield construction efficiency is easily affected by the stratigraphic environment and tunnelling control parameters.In-depth research on tool breaking mechanism,optimization of tunnelling parameters control and improvement of tool adaptability in sand and pebble strata become urgent problems to be solved.In order to investigate the shield cutter in sand and pebble strata with cutting law,firstly,the shield cutter cutting mode is analyzed,and the cutting force calculation model is resolved according to the soil damage theory at Rankine passive equilibrium.Then establish the cutting model of shield cutter and prior cutter in sandy cobble strata,and evaluate the cutting force and plowing loosening efficiency as the cutting index of the tool.The numerical simulation results show that when cutting rock and soil at low speed,the cutting speed of the tool has less influence on the cutting force,and the highest tillage efficiency is 25.38% when the relative depth of cut is 20-30 mm,and the highest tillage efficiency is27.78% when the relative tool distance is 125-150 mm,so the adaptability and economy of the tool is better at this time,which provides a design basis for the optimization of the shield cutter.Based on an interval tunnel shield project of Beijing Metro Line 12,the construction risk level of 38 environmental risk sources in the interval was classified based on the analysis of the change law of shield tunneling parameters in sand and pebble strata,and a complex artificial neural network model with environmental impact parameters of strata and shield tunneling control parameters as input and total thrust,cutter speed and tunneling speed as output was established based on BP neural network.The artificial neural network model of shield excavation parameters under risk sources is established.The prediction results show that the overall average absolute error of the model is 6.2%,and the average errors of the output parameters are 8.3%,1.8% and 8.5% respectively,which provide guidance for the selection of shield tunnelling construction parameters.In order to verify the reliability of the numerical simulation law,an indoor shield tunneling experiment device was developed independently to carry out shield tunneling experiments under the conditions of sand and pebble strata and cutting concrete blocks.After 60 h of wear experiments,the time-wear curves were fitted for the speed of 60,80 and100 rpm under the two working conditions.After the microstructure analysis of the wear surface,the cutting surface of the tool is mainly subject to abrasive wear,and the tool disc is subject to both abrasive wear and adhesive wear,and the reliability of the numerical simulation results is verified by the experimental plowing efficiency of the optimally designed tool after cutting the palm surface.In this paper,from theoretical analysis,numerical simulation,artificial neural network prediction,indoor experiments and field experiments,we propose shield tool optimization measures for sand and pebble strata to significantly improve tool tillage efficiency and guide construction parameter control to improve tunneling efficiency and shorten construction cycle,which is of great significance for shield construction.