Study On The Calculating Models Of Key Parameters & Mechanical Behavior Of The EPB Shield Machine

As the rapid development of subway constructions in cities,designing and developing shield machines in China is at starting phase,and so a systematic theory for designing the shields has not been developed.As a result,research levels on many aspects are behind the Western,such as interactions between the shield and ground and between loads and mechanical behaviors of the shield.In addition,few existing models can systematically predict the key parameters of the shield-machine-jack thrust and cutter torque.As the change of the geological conditions and diameter of a tunnel in excavating,it's difficult to determine the key parameters.The reason for this is that there are few theoretical models to describe the key parameters.In the present study,we study interaction between shield and ground.The purpose for the study is to found a theoretical basis for developing and manufacturing shield machines in China and for designing and selecting types of shields,associated with correctly choosing the parameters of the machine.Some achievements were made in the present study as follows:1.The influence factors of cutter torque were studied systematically, and a new prediction model for the cutter torque had been developed. The model shows that those new factors influencing on the cutter torque should be taken into account,i.e.,the frictional resistance torque on the back of cutterhead and the shear resistance torque of the muck in hatch of cutterhead and mixing round torque of the cutter head's beam and The calculating formulae of those torque components in the model were deduced.Comparisons between predicted and observed data verify the validation of the model.This prediction model found a fast theoretical basis in determining the cutter torque of the shield.2.Bsed on shield engineering practice and measuring field data,a example has done to calculating cutter torque by the model.Main factors influencing on cutter torque have been studied by analyzing composition of cutter torque,magnitude of torque components and it's proportion in total torque.It also been studied for parameters in model to influence on cutter torque,which have provide theoretical guide for the type selection,design of shield and it's application.3.A prediction model on the jack thrust of the shield has been developed. The new calculating formulae were deduced by using mechanics theory and math method to the thrust resistance on the face of cutter head and on the shell of shield in the model.They replace simplified calculating formulae before.So the accuracy for predicting the jack thrust in the new model is higher than the existing models,more influence factors in assessing the jack thrust is accounted for.The relationships between the jack thrust of the shield and some parameters were expressed systematically in the model,i.e.,the size of the shield,layers and thickness for each layer,density and friction angle of the soils,etc.This prediction model found a fast theoretical basis in determining the Jack thrust of the shield.4.In order to control the behavior of shield availably,a model of mechanical behaviors of the articulated shield has been developed.The model expresses three relationships of behavior of the articulated shield,ground properties and shield mechanisms(jack thrust),which have provide a new way to control shield direction.5.The interaction between the behaviors of the shield and ground deformation has been studied.Additionally,the interaction between the ground displacement and earth pressures acting on the shield periphery has been studied.The ground reaction curve is achieved by using 2D FEM analysis for the shield tunneling.It also founds a theoretical basis for developing a mechanical behavior model of the articulated shield6.Shield tail is most weak structure of shield skin.Based on loads-structure method,the calculating formulae of moment and axes force has been deduced for every single load acting on the shield tail. These calculating formulae have been verified by 2D plane strain FEM model with more spring fulcrums showing the interaction between shield and ground.7.The influence factors of cutter wear were studied in shield tunneling. The definition and calculation method for tunneling distance life of cutter and wear-tear coefficient were proposed.The prediction curve between the wearing value of cutter and excavation distance life were obtained.