Pile-soil stress ratio is an important index in the research of composite foundation. Currently

the studies regarding the pile-soil stress ratio mainly focus on the general composite foundations

such as mixing pile and gravel pile. However

the theoretical calculation of stress concentration ratio of stiffened deep mixed (SDM) pile has been rarely reported. From the deformation modes of soil

cement and the composite pile element

the negative friction resistance of pile

pile cap and pile tip penetration to bearing layer is considered comprehensively

the compression deformations of soil around the pile

cement soil pile and composite pile body are analyzed

and a stress ratio calculation formulation is derived to describe the relationships among stiffened deep mixed composite foundation piles

cement soil pile and soil. Further

the effects of core pile diameter of stiffened deep mixed pile

core pile length and soil cement pile length on the pile-soil stress ratio are analyzed. It is found that the pile soil ratio increases with increasing the core pile diameter

length of stiffened deep mixed pile and pile length of cement soil. By comparing the computed results with the field data from a field test

the computed results and measured data agreed well and the reliability and feasibility of the proposed method was verified

which can be beneficial to guiding the actual practice.