Since large scale construction of underground railways was carried out in Tianjin

more and more deep foundation pits have been to be excavated in soft soils. In the period of excavation activities

it is very important to give a suitable control criterion to ensure the pit stability. To find out the recommended criterion value

some comprehensive measurements have been made in some typical pit engineering during the construction of No.1 Line. The observed data of earth pressure

retaining structure displacement

ground surface settlement and water pressure have been picked up and analyzed. A finite element method has been adopted to simulate the procedure of pit construction. By comparing the calculation results with the observed data

the calculation model has been optimized; and calculation parameters have been determined. The established approach has been applied to simulate the failure procedure of deep foundation pit. The main influence factors including the displacement of retaining structures

the length of retaining structures and the force in braces

have been analyzed. The ratio of retaining structure displacement and maximum ground surface settlement over pit depth are recommended as the control criterion of pit stability during construction.