Abstract: The application level of steel support axial force servo system are needed to improve  and their ability to control deformation should be given full play. The elevated structure Heping Station foundation pit of Shenzhen Urban Rail Transit Line 12 undergoes the intercity railway. Based on this project and with the method of numerical simulation and theoretical analysis, the paper conducts a systematic study on three aspects of servo system, namely, the determination method of the axial force setting value, arrangement and node calculation. Thus a complete set of servo system application method is formed. The results show that: (1)The reasonable axial force setting value of each steel support can be determined by using the doublecontrol method to guide numerical simulation calculation. (2)The effect of servo system depends on its quantity and position. Under a certain number of conditions, the lower the average elevation of the servo system is, the better the deformation control effect is, while the control efficiency of the shallow servo system is poor. (3)For servo straighteners with diameter of 800 mm and wall thickness of 20 mm, ordinary bolts of level 4.6 or level 4.8 can meet the stress requirements. For steel enclosing purlin at both ends, it is suggested to add two stiffeners behind the contact range between steel and support pipe joint to improve deformation and stress state. The hoop structure can effectively restrain the lateral buckling deformation of the pipe joint system, and it can give full play to its deformation control ability at the equinox.

Key words: foundation pit, servo system, steel support, node calculation, axial force setting value, arrangment, numerical simulation