Study on Duncan-Chang damage constitutive model of saturated compacted loess

The instantaneous settlement of high railway foundation in loess area is closely related to the mechanical properties of saturated compacted loess. The constitutive relationship of saturated compacted loess is an important way to characterize its mechanical properties; however, Duncan-Chang constitutive model is difficult to accurately describe the strain softening characteristics of compacted loess after failure. To improve the adaptability of Duncan-Chang constitutive model, statistical damage theory is introduced to establish Duncan-Chang damage constitutive model of saturated compacted loess. Qp₃ loess in Xiyan high-speed railway filling area was selected to carry out consolidation undrained triaxial tests with different compaction degrees. The vumat subroutine was then written for verification. The triaxial test of saturated compacted loess and the finite element numerical simulation of subgrade settlement under different compaction degrees and filling slopes were conducted. The results show that the compacted loess in the filling area shows strain softening characteristics when it is sheared. The peak strength and initial deformation modulus increase with the increase of compaction degree, while the increase of peak strength decreases with the increase of compaction degree. The increase of initial deformation modulus increases with the increase of compaction degree. The vumat subroutine based on Duncan-Chang constitutive model with statistical damage is used to verify the shear strength of compacted loess in triaxial test, and the results are consistent, indicating the mechanical characteristics of strain softening of compacted loess in filling area. Through vumat calculation, the settlement of filled subgrade decreases with the increase of compactness and increases with the increase of fill slope. This study can provide basic information for the calculation and analysis of the instantaneous settlement of fill subgrade in the loess area.