The support system of foundation pit is divided into three isolated models related by their boundary conditions

which include active soil around support structure

support system and passive soil under the bottom of the pit. As plane strain problem

the active and passive soils are meshed as solid elements

support piles are meshed as beam elements. If the piles worked with bolts or struts

the bolts and struts are meshed as truss elements connected with beam elements. Then each model could be solved respectively; but share common boundary conditions. Giving the initial condition as the horizontal displacement of the piles equal 0

then the displacement could be solved by iterative method. If the displacements between two loops are nearly same

the iterative process ended; and the forces and displacements of the piles in stable state could be achieved. Displacement iterative method objectively reflected the dynamic interaction process between soil and support structure. This method is applied to an actual case; the calculating results are well coincident with the measuring data.