Study On The Coupling Action Between Cutterhead And Stratum Of Shield In Sand-pebble Stratum

The sand-pebble stratum is one of the main strata in Beijing subway construction.It has high density and high saturated compressive strength.The contradiction between the rapid wear of cutterhead and the long distance of single excavation is prominent in the process of shield tunnel construction,which is one of the key problems to be solved urgently.At present,the research on the cutterhead driving mechanism only considers the physical and mechanical properties of the formation,and ignores the unevenness of the stress required for the fracture of the formation at different locations.In this paper,from the perspective of controlling and using the stress state of the palm face,the research on the coupling mechanism between the cutterhead and the formation can be carried out,which can provide a reference for the design of the efficient cutterhead and shield construction.In this paper,firstly,according to the physical and mechanical characteristics of sandpebble soil,the index for evaluating the difficulty of excavation of sand-pebble stratum under shield construction method is proposed.Then,from the perspective of the interaction between the shield cutterhead and the stratum to be excavated,the research on the coupling mechanism of the rock machine is carried out,and the objective function of the optimal design of the cutterhead structure is proposed accordingly.Finally,relying on the working conditions of a shield tunnel section of Beijing Metro Line 19,using the finite element analysis software ABAQUS,a numerical analysis of the stress distribution law under three typical palm face shapes was carried out,and the cutterhead dynamics under actual conditions were also studied.The process of cutting formation was simulated and analyzed.The main research results are as follows:(1)The main failure mode of sand-pebble soil is peeling due to its poor particle grading and loose overall structure.In this kind of stratum,the spoke type cutter with large opening rate is mainly used,and the cutter is mainly cutting cutter,advance cutter and center cutter.The damage degree of sandy pebble stratum can be expressed by the drivable strength (?).When the shape and arrangement angle of cutting unit and the nature of soil are certain,the parameter is related to the shape of face.There is no change in the shape of plane type face,but in the shape of concave type face,there is a larger value in the lower part of stratum,while in the shape of convex type face,there is a smaller value in the outer part.(2)In the process of rotating cutting,the function envelope of each tool is continuous to a whole cutting profile.The cutting profile of a certain shape should be the shape of a certain shape of the face.Because of the different shape of the face,the (?) of each position on the face is different.At the same time,the cutting process of each tool in unit time is different due to the different turning radius of each tool on the disc different,the greater the radius of rotation,the greater the amount of tool wear.The interaction and interaction between the cutterhead and the formation can be described as the principle of rock machine coupling.From the point of view of the work and energy consumption of the cutter head,it is proposed to take the breaking work per revolution of the cutterhead as the objective function of the structure optimization of the cutter head.(3)In the first three seconds of the smooth loading process,when time to 0.9s,some of the soil on the face reaches the critical point of damage and deformation,and the corresponding soil at the position with larger rotation radius first enters the stage of damage and failure,and the (?) of the hand formed by the cutter head conforms to the distribution rule of plane shape of the face.There is a linear relationship between the actual cutterhead wear and the cutting stress intensity of the face.The maximum difference of the shell cutter wear at different positions on the same spoke is 6.5mm,and the cutter wear reaches 3.2mm.The uneven wear is serious.Finally,according to the above coupling principle of rock machine and the actual wear situation,some suggestions are put forward for the optimization of cutter layout and outer contour structure of the cutterhead.