Design-oriented comparison and load adaptability of deep cement mixing columns with different cross-sectional geometries for soft-soil bridge foundations

Abstract Deep Cement Mixing (DCM) columns are widely used for improving soft-soil bridge foundations, but the influence of cross-sectional configuration is commonly assessed at a single design load. In practice, bridge-pier loads vary during service, and design configurations that satisfy the same bearing-capacity requirement may exhibit different deformation, stress, and material-use responses. This study investigates circular, square, and rectangular DCM configurations for a soft-soil bridge foundation in Wanning, Hainan, China. For each cross-sectional geometry and area replacement ratio, the minimum required column length was determined to satisfy the same bearing-capacity requirement under a 240 kN design load. A three-dimensional finite-element model was developed in ABAQUS using the Mohr–Coulomb model for natural soils and linear-elastic models for the cement-treated columns and cushion. The model was checked against an analytical settlement solution and compared with the available field settlement measurement from a 196 kN static load test, for which the numerical prediction differed from the measured value by 14.5%. A total of 63 cases were analyzed for area replacement ratios between 0.30 and 0.50. At a replacement ratio of 0.30, the circular, square, and rectangular configurations produced settlements of 25.44, 27.78, and 32.41 mm, respectively. The circular configuration provided the lowest settlement, whereas the rectangular configuration required the smallest volume of cement-treated soil. With increasing replacement ratio, the required column length and maximum DCM stress generally decreased, while the cement-treated soil volume increased. Settlement did not decrease monotonically because the column length was simultaneously reduced to satisfy the same bearing-capacity criterion. Additional analyses under pier loads from 180 to 240 kN showed that the circular configuration was less sensitive in terms of settlement, whereas the rectangular configuration exhibited lower stress sensitivity. The results indicate that selection of DCM cross-sectional configuration should account for bearing-capacity requirements, settlement, stress level, material demand, and variation in service load.