Study of the mechanical properties of double line pipelines under silty sandstone and pipeline coupling

To investigate the influence of the filling thickness and internal water pressure on the stability of a water supply pipeline, a typical pipeline section 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.