Based on the twin shear unified strength theory

and using vertical displacements equality

lateral deformation compatibility and continuum between gravel column and surrounding column soil in the composite foundation

stress-strain state of the composite foundation with gravel columns is analyzed by the elastoplastic theory under vertical load. Ascertaining methods for weight coefficient b are established. Influences of weight coefficient b on bearing and deformation character of the composite foundation are discussed. A series of analytical formulae

for example

between load exerted on the composite foundation or share load of gravel column or compression value of the reinforcement area and plastic area radius of surrounding pile soil

are drived. Design idea of double control on bearing capacity and settlement is suggested for the composite foundation with gravel columns. To make sure feasibility proposed method

results of model tests are compared with those of calculation; the comparison indicates that the proposed method has guidance significance for the composite foundation design with gravel columns.