Abstract: When lime-soil composite foundation bearing load, the expansion deformation of lime-soil piles would compact soil around and exert pressure on soil and piles. To enhance the reinforcement effect of the lime-soil composite foundation, it is critical to identify the radius of compacted zone. Based on the unified strength theory and taking the conditions of compatible deformation of soil and piles into consideration, the formula describing the relationship between settlement of composite foundation and radius of compacted zone has been derived. Furthermore, the various elements influencing compacted zone radius and the trend of the zone radius changing under different values of b, different pile diameters, and different foundation depths are discussed as well. The research results indicate that the radius of compacted zone decreases with the increase of foundation depth when the b value and pile diameter are invariable. The results also show the optimal range of compacted zone along the composite foundation depth is from the pile top to the 1/3 length of pile. The radius of compacted zone varies from 1.51d to1.68d under different conditions of b value, where d is the diameter of pile. And radius of compacted zone expands along with increase of the pile diameter d, when the b value and foundation depth are invariable. To exert the strength of material such as soil, the solution considered the intermediate principal stress has positive effect on the ultimate strength of material.

Key words: unified strength theory, composite foundation, lime-soil pile, radius of compacted zone, plane strain