Installation of deep mixing columns causes lateral displacement and induces high excess pore pressures in surrounding soils.The relationship among the injected volume of cement slurry

the expanding pressure

and the column diameter was analysed.The result indicates that 5%-10% injected slurry volume can induce expanding pressure of 1.8 to 3 times the undrained shear strengths

and the diameter of column expands 5% to 10%.Then

the relationship between the injected slurry volume and the real diameter was presented after investigating diameters of the model column in laboratory test and the diameters of the field mixed column.For short columns（diameter/length <10）

it shows that about 45% injected slurry volume was lost due to soil heaving during mixing

about 5% injected slurry volume penetrated into the surrounding soils through fractures

and about 50% injected slurry volume was transformed to the column diameter and made the column expanding 5% to 10% of its original diameter.These results indicate that the expansion makes the real diameter 5% to 10% greater than the nominal diameter of mixing blades.