Study On Reduction Of Cutterhead Torque In EPB Shield With Soil Conditioning

Along with the rapid development of underground construction in recent years, shield tunneling method, as a safety and efficient tunneling technique, is becoming a comprehensive way to build the subway. Among the shield tunneling methods, Earth Pressure Balanced Shield tunneling (EPBS) is becoming the main tunneling technique with its technical and economical advantages. For a smooth EPB drive the soil in the pressure chamber must been mixed to a uniform state, therefore many mix blades are installed in the chamber. This is the reason why the EPB shield requires a torque 2-3 times larger than the other types of shield machines to turn the cutterhead. Nowadays long distance and large diameter are the two tendencies of the tunneling construction. Large cutterhead torque has been the bottleneck for the development of EPB shield, which has attracted attention in the engineering world.In the EPB tunneling projects, soil conditioning has been widely used to reduce the drive torque of cutterhead. Nevertheless this practice depends thoroughly on the engineering experiences. But the researches of this subject are relatively backward. Lack of the cognition for the mechanism about the reduction of EPB cutterhead torque with soil conditioning, the manufactures of EPB machines can not consider this factor of soil conditioning when they design the machines. That induces a great energy waste.To aim at the above problems, the research works have been carried out. The main contents of this paper can be summarized as follows:(1) Study of the factors and building of a mechanic model of the cutterhead torque on considering the features of EPB cutterhead. Study on the key factors of soil characteristics for the cutterhead based on the model.(2) Study of the compatibility of the foaming agent and the soil characteristics based on the soil conditioning technique. Development of the foam additives for the sand and the clay.(3) Research of the relationships among the characteristics of foam, the characteristics of foamed soil and the mixing torques based on the experiments of soil conditioning. Research of the influences of Foam Expansion Ratio (FER) and the stability of foam to the cutterhead torque.