Settlement calculation of stone columns-improved composite foundation based on secant modulus

The stress-strain relationship of soils under confining conditions is hyperbolic. In this case, secant modulus can be adopted to calculate the vertical strain of soils, which is helpful to realize the settlement calculation. The secant modulus of the soil around stone columns was determined according to the relationship between the secant modulus and the compression index and compression modulus. The column-soil stress ratio considering the nonlinear compressibility of soils was proposed based on the assumption of equal strain, and the improved stress correction method and composite modulus method for nonlinear settlement calculation of composite foundations with stone columns were further provided. The two improved methods for the settlement calculation were verified by the model test and actual project. The results show that for the laboratory model test, the differences between the measured results and the calculated results by the improved composite modulus method and modified stress correction method are less than 1.00 mm, which indicates that the improved method for settlement calculation is reliable. For the actual project, the error between the improved composite modulus method and the measured results is 8.70%, which is less than the specified error of 55.06% by the composite modulus method in the JGJ 79—2012. The error between the improved stress correction method and the measured results is 8.73%, which is less than the specified error of 55.11% by the stress correction method in the JGJ 79—2012. The comparative analysis shows that the improved settlement calculation method is better than the composite modulus method and stress correction method in the JGJ 79—2012, and the calculated results by the improved method are closer to the measurement results, which indicates that the improved method has better reliability and applicability.