Study on Deformation Response Characteristics of Horizontal Main Pipeline During Vertical Jacking

The vertical jacking method is a trenchless construction technique in which standpipes are jacked upward from a horizontal main pipeline through overlying soil, and it is widely applied in marine outfall projects. Taking a deep-sea tailwater outfall in Ningbo as the case study, this research develops a three-dimensional finite element model using ANSYS 2021 R1 based on actual geological and construction conditions. The settlement and stress responses of the horizontal main pipeline during jacking are analyzed and validated against field monitoring data. The numerical results agree well with the field measurements, with an average error of 7.29% for settlement and less than 9.83% for circumferential stress. The main pipeline exhibits a settlement pattern characterized by larger deformation in the middle and smaller at both ends, with a maximum value of 0.90 mm, decreasing with distance from the opening ring. Circumferential stress initially increases and then stabilizes, with maximum tensile and compressive stresses of 0.082 MPa and 0.056 MPa, respectively. Overall stress levels remain well below structural strength, indicating that structural damage is unlikely under the investigated conditions. These findings provide a case-based reference for structural design, construction control, and monitoring layout in marine outfall projects with similar geological and construction conditions.