Based on the deep shaft projects in deep tunnel

the deformation characteristics of circular and rectangular foundation pits were compared and analyzed.The deformation inhibition mechanism of the circular shaft foundation pit was discussed by statistically analyzing the typical cases of the circular shaft foundation pits at home and abroad.And the deformation control index of circular shaft foundation pit was determined based on existing codes and engineering examples.The results show that:（1）The calculated internal force and deformation of the underground diaphragm wall of circular shaft considering space structure system are 20% smaller than those of the elastic foundation beam

which is superior to the rectangular foundation pit.（2）The comprehensive action of cylindrical effect

reinforcement of weak points by axial force and extrusion effect of soil on supporting structure is the reason why the mechanical deformation of a circular foundation pit is restrained.（3）With the increase of foundation pit depth

the ratio of horizontal displacement to depth of foundation pit side wall decreases significantly.With the increase of foundation pit diameter

the ratio of horizontal displacement to depth of foundation pit side wall increases.（4）The depth of 35 mand diameter of 40 mshould be set as the demarcation point for the foundation pit

and 0.5‰

1‰ and 1.8‰ should be selected as the horizontal displacement controlling indexes for the circular deep foundation pit supporting structure according to the actual situation.