Abstract: 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 λ  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 λ  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 λ  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.

Key words: soil arching effect, maximum principal stress, pile spacing, load sharing factor