To investigate the influence of the filling thickness and internal water pressure on the stability of a water supply pipeline, a typical pipeline of the Sun Mountain Water Supply Project is selected as the research object. A numerical simulation method is adopted to establish a three-dimensional finite element model integrating a double-line pipeline-artificial fill-foundation to study the influence of different single-layer filling thicknesses and internal water pressures on the mechanical properties of the double-line pipeline. The results of the study show that the relative error between the intrinsic mode of the finite element model of the double-line pipeline and the frequency identified by the dispersion entropy variational mode decomposition (DVMD) method on the measured vibration signals is only 1.55%, which confirms the validity of the finite element model and the accuracy of the results. With increasing soil filling and increasing single-layer filling thickness, the vertical displacement of the double-line pipe gradually increases, with a maximum value of 12.24 mm. With increasing single-layer filling thickness, the rate of increase in the vertical displacement of the double-line pipe increases. With increasing soil filling, the tensile and compressive stresses on the double-line pipe increase gradually, with maximum values of 0.148 MPa and 0.568 MPa, respectively. When the number of cycles is the same, the tensile and compressive stresses of the pipe sheet increase with increasing single-layer filling thickness. When the internal water pressure is 0.6 MPa, the trends of the inner and outer circumferential deformation and tensile and compressive stresses of the left and right lines of the pipes are basically the same. The outer stresses are lower than the inner stresses, among which the tensile stresses are reduced by 25% and 20.1%, and the compressive stresses are reduced by 16% and 18.2%, respectively. Under the joint action of the earth pressure and internal water pressure, the deformation of the double-line pipeline and the compressive stress tended to decrease and then increase, and the tensile stress gradually increased. The research results provide a theoretical reference and basis for similar water supply pipeline projects.

This study investigated the bearing capacity and failure characteristics of a shield tunnel lining structure subjected to top overload and simultaneous unloading on both sides of a tunnel, considering the presence of internal water pressure. The results show that the structural response of the shield tunnel lining is most unfavourable under the condition of a fully filled pipe, where the internal water pressure reduces the axial force of the lining ring section, compared with the conditions of an empty pipe and a partially filled pipe. When the internal water pressure increases from 0 MPa to 0.6 MPa, the convergence deformation of the lining ring under a top overload of 400 kPa increases by 23.6%, resulting from a reduction of 27.2% in the maximum axial force at the lining section. Similarly, the convergence deformation of the lining ring under simultaneous unloading of 400 kPa on both sides of the tunnel increases by 21.6% because of a reduction of 56.4% in the maximum axial force at the lining section. The shield tunnel lining rings under the action of internal water pressure when subjected to top overload or simultaneous unloading on both sides of the tunnel exhibit the same failure characteristics. As the overload or unloading value increases, the lining ring deformation gradually increases, the joint opening exceeds the waterproof design limit, and the bolt enters a plastic yield state as its stress exceeds the yield strength. Cracks occur in the concrete at the positions of the lining segments, segmental joints, and handholes because of the large strain values. Moreover, the stress of the steel bars, joint panels, and anchor bars inside the lining segments may exceed their yield strength. During the top overload, the bending moment and axial force of the lining ring increase, whereas when unloading on both sides of the tunnel, the bending moment increases and the axial force decreases. Compared with the case with an overload value of 400 kPa, the maximum positive and negative bending moments of the lining ring under a lateral unloading value of 400 kPa decrease by 11.5% and 14.4%, respectively, whereas the maximum axial force decreases by 73.1%. This considerable decrease in axial force during lateral unloading leads to greater eccentricity and a more adverse structural response of the lining structure than does top overload. Therefore, during the operation of shield tunnels with internal water pressure, the influence of unloading on both sides of the lining structure caused by soil stress relaxation should be taken seriously.