Based on Clough system stiffness model

this paper introduces a novel synthetic stiffness expression of strut system for excavation. This expression considered the wall stiffness

strut stiffness and the soil stiffness behind the wall

and thus it had substantial advantage to predict the deformation induced by excavation. Clough system stiffness

Bolton system stiffness and the synthetic system stiffness proposed in this paper were applied to measure the tilt of 469 retaining walls in 22 deep excavations of Tianjin subway line 6 engineering. The maximum deformation of the retaining structure in foundation pit decreased with the increase of the stiffness η? of the dimensionless composite support system. The deformation value tended to be constant

until η? increased to a certain value. When the mobilized undrained shear strength ratio of soil was further analyzed

it is found that the ratio of the soil behind the wall along Tianjin subway line 6 was less than 0.6. The upper limit value of this ration is 0.8

which indicates that the excavation engineering of Tianjin subway line 6 has sufficient safety reserves. Therefore

research results can provide significant reference for the economic and safety design of similar engineering.