The excavation of foundation pit involves both horizontal and vertical unloading processes. In order to investigate influence of each directional unloading on displacement and internal pressure of the retaining structure

a foundation pit is analyzed via the FEM simulation of the corresponding modified Duncan-Chang model

under respective unloading of horizontal or vertical pressure. It is shown that the horizontal displacement of retaining structure is largely caused by the horizontal unloading; while the vertical unloading is responsible for the negative internal force. Consequently

this study provides an explanation about the often-observed fact that measured internal pressure in the field is always lower than the one expected in the design.