In order to study the mechanical response characteristics of soil support of foundation pit under the combined action of different types of retaining piles. Based on the foundation pit project of Linjiazhuang Station

Line 4 of Jinan Rail Transit

and aiming at the composite support form of steel pipe pile and cast-in-place pile adopted for the first time on site

the analytical analysis model and calculation method of stratum support stress under the action of composite piles are proposed. The distribution characteristics of the maximum principal stress and the rule of arching effect under different formation depths and pile spacings are analyzed. On this basis

according to the relationship between the maximum principal stress support line and the soil arch axis between piles

an arch analysis model is put forward

in which the inner arch and the outer arch bear the lateral earth pressure together

the theoretical formulas of reasonable pile spacing S and load sharing coefficient are derived

and the load-bearing capacity relationship between steel pipe pile and cast-in pile is discussed. Finally

the effectiveness of the soil arch analysis model is verified with concrete engineering examples

and the influence of different parameters such as internal friction angle

cohesion force

and pile diameter on reasonable pile spacing S and load sharing coefficient is analyzed. The results show that the reasonable pile spacing S increases with the increase of internal friction angle

cohesion force

and pile diameter under the composite support design. The load sharing coefficient increases with the increase of internal friction angle and cohesion

and the load bearing capacity of the outer arch gradually increases. When other parameters remain unchanged and the diameter of steel pipe pile increases

the load bearing capacity of outer arch will gradually decrease.