Study on settlement deformation law of new and old subgrade of expressway reconstruction and expansion based on CPTU

In the reconstruction and expansion of expressways in soft soil areas, controlling the differential settlement between the new and existing subgrades is of vital importance. To investigate the settlement and deformation characteristics of both the new and existing subgrades, piezocone penetration test (CPTU) and dissipation tests were conducted on these subgrades. The CPTU dissipation data was utilized to determine the soil’s degree of consolidation, and settlement calculations for the new and existing road subgrades were based on the CPTU test results. Subsequently, a finite element model was developed using the CPTU test findings to analyze the horizontal displacements, vertical settlements, and differential settlements of the new and existing subgrades before and after the reconstruction and expansion. Based on the measured settlement results, the new and old subgrade settlement calculation results are verified. The outcomes revealed that the degree of consolidation for the existing road subgrade of the Lianhuai Expressway ranged between 42 % and 96 %. The maximum horizontal displacement of the subgrade pre- and post-expansion occurred at the slope toe. Before expansion, the maximum vertical settlement was observed along the road’s centerline, while after expansion, it was located in the centerline of the widened section. The maximum additional settlement amounted to 274.77 mm. During the new road construction phase, the differential settlement between the new and existing road subgrades increased rapidly over time, peaking at its maximum value. However, during the operational phase of the new road, this differential settlement tapered off as time progressed.