| With the widely use of city tunnels, shield tunneling machines have become indispensible tools in the process of tunneling. Some concerning experts have predicted that the 50% global tunnel construction will be in China in the future.However, constructing in sandy cobble stratum is a major issue for shield tunneling. While the shield machine is working in the stratum, its cutter head can frequently fail and tool wear can seriously occur to the machine, which can lead to not a little economic burden to the construction project, accounting for one-third of the total cost. What’s worse, the shield machine needs a high cutter head torque and propulsive force in the process of constructing in the sandy cobble stratum. For example, in some shield project, the maximal propulsive force of the shield machine reached 34000KN, and the maximal cutter head torque got close to 5100KN·m, all of which made the cutter head frequently overloaded, thus further aggravating the tool wear.This thesis, which studies the sandy cobble stratum, aims at the problems that the shield construction of sandy cobble stratum is now confronting. It proposes a new method about rock breaking of "milling- dispersing- low-speed grinding" in order to reach the aim of reducing tool wear and cutting down energy consumption of shield machine in the case of situation of sandy cobble stratum. The concrete research contents are as follows:(1) This thesis carries researches on sand pebble strength characteristics including uniaxial compressive strength, shear strength and long-term compressive strength. Studies the of disc cutter mechanism, rock breaking mechanism of slicer and rock breaking force, while analyzing the load of sandy cobble stratum cutter head. Introduces the construction difficulties of the shield in sandy cobble stratum and does a research on the reason of tool wear and cutter head defaults.(2) Aiming at the problems that the shield construction of sandy cobble stratum is now confronting, it proposes a new method about rock breaking of "high-speed milling- dispersing-low-speed grinding", the main content of which is at first installing milling tools on the cutter head and use the milling tools to cut rocks on their original surfaces into strip grooves(called discredited) before other tools and then using disc cutters to grind excavation faces, which makes the cutwork of shield tunneling machine easier, reduces the tool wear, saves shield tunneling energy consumption and increases drivage efficiency.(3) In order to realize the new method about rock breaking of "high-speed milling-dispersing- low-speed grinding", this thesis designed a sprocket drive mechanism for the shield tunneling machine to make power transmission come true.(4) Use ANSYS Workbench to make analog simulations of grooves’spacing of discrete rock surface, relation of diameter of disc cutter and friction force.A conclusion was got:friction force of disc cutter reduce 77% when the surface of stone is scattered and its gap and diameter of groove is 100mm,60mm respectively.(5) Use ANSYS/LS-DYNA to make explicit dynamics analysis of the rock breaking process of disc cutters, make analog simulations of the relationship between discrete rock surface and rock breaking force, a conclusion was got:rock breaking force of disc cutter reduce 75%and 90% respectively when the surface of stone is scattered.(6) According to the result of simulation and base on the study of research results of the early researchers, this thesis analyzes the reduction rate of wearing capacity and specific energy consumption of rock breaking after rock surface is scattered, we got a conclusion:specific energy consumption and wearing of disc cutter reduce 95% and 73% compare with traditional method of rock breaking.
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