Wear Mechanism And Prediction Model Of Shield Tunneling Tool In Sand And Pebble Formation

The wear mechanism and wear prediction of shield tools is an important subject of Shield Engineering in sandy gravel stratum.It has both theoretical and experimental significance for accurately predicting the service life of shield tools and guiding construction.Based on the shield tunneling project between Hatching Garden and South Railway Station of Chengdu Metro Line 18,the wear mechanism,wear prediction and wear factors of shield tools in gravel stratum are systematically studied by theoretical analysis,deduction and SEM image analysis using the measured data.The main research contents and conclusions are as follows:(1)Summarize the wear forms and types of hobs,and analyze the wear mechanism of hobs by macroscopic observation and scanning electron microscopy.It is concluded that the main wear mechanisms of hobs in gravel stratum are plastic removal mechanism,brittle fracture mechanism,adhesion wear and fatigue wear.Through the analysis of the wear volume per unit rock breakage,the cutter head is divided into central area,front area and edge area to fit and calculate the weight of different wear types,and to verify the engineering data.(2)The rock-breaking force model of constant cross-section hob is established.The validity of the model is proved by comparing with CSM wear,Rostami model and Colorado experimental data.The equation for calculating the rock breaking distance at one point on the front and side of the cutter ring is established.On the basis of force model and motion model,combined with tribological wear theory,the wear dynamic prediction models of the center,front and edge of the cutter head are established respectively.The relationship between radial wear,lateral wear and shield tunneling distance is calculated by programming with MATLAB software,and the relationship between radial wear and penetration and tool installation radius is analyzed.Comparing the calculated value of radial wear with the measured value of shield tunneling in gravel stratum,the accuracy of the prediction model is demonstrated,and the wear rate of the next tool change is predicted.(3)depending on the data of shield tunneling in Chengdu Metro Line eighteen,the proportion of sand gravel stratum,cutter torque,cutterhead thrust,cutterhead speed,driving speed,penetration rate,soil pressure and foam injection amount were selected.The correlation between the amount of cutter wear and geological and mechanical factors was quantitatively analyzed,and the reasonable selection scope of tunnelling parameters for sandy cobble stratum was put forward.Through data statistics and component extraction,a tool wear calculation model based on tunneling parameters is established by using partial least squares method.(4)According to the engineering characteristics of shield tunneling in sandy gravel stratum and combined with the tool wear in sandy gravel composite stratum engineering,a scheme of optimizing cutter head and tool allocation,construction control of tunneling parameters and treatment of anti-caking mud cake in composite stratum is put forward to guide construction,with a view to reducing tool wear,improving stratum adaptability and improving construction efficiency.