To restrict the thermal expansion displacement of X80 tunnel pipelines, anchor blocks are commonly designed and installed at entrances and exits of tunnels, which makes the anchor block design one of the most important issues. As well known, the key step for anchor block design is to calculate the thrust acting on the anchor block caused by the thermal expansion displacement. In this paper, an analysis method of the thrust is proposed, considering the effects of the vertical earth pressure, transverse horizontal earth pressure, internal pressure, temperature variation, and pipeline–soil friction. Using the condition of deformation compatibility and the hypothesis of stagnation point, the axial force of tunnel pipelines is derived by the unit force method. By combining the compatibility condition between the transition segment length of anchored side pipelines and the displacement of anchor blocks, the thrust acting on anchor block is derived. Using the analytical method and finite-element software...

In this paper, a single-slope tunnel pipeline was analysed considering the effects of vertical earth pressure, horizontal soil pressure, inner pressure, thermal expansion force and pipeline—soil friction. The concept of stagnation point for the pipeline was proposed. Considering the deformation compatibility condition of the pipeline elbow, the push force of anchor blocks of a single-slope tunnel pipeline was derived based on an energy method. Then, the theoretical formula for this force is thus generated. Using the analytical equation, the push force of the anchor block of an X80 large-diameter pipeline from the West—East Gas Transmission Project was determined. Meanwhile, to verify the results of the analytical method, and the finite element method, four categories of finite element codes were introduced to calculate the push force, including CAESARII, ANSYS, AutoPIPE and ALGOR. The results show that the analytical results agree well with the numerical results, and the maximum relative error is only 4.1%. Therefore, the results obtained with the analytical method can satisfy engineering requirements.

During buried pipelines, two construction modes are used, namely, sinking and lowering pipeline into being-dug trench by self-weight, lifting and lowering pipeline into pre-dug trench by hoist. For pipeline sinking and lowering-in, the analytical model was derived especially considering the soil displacement at the end boundary of being-dug trench. For pipeline lifting and lowering-in, the control condition to calculate the lifting force was firstly given based on the extreme displacement of the pipeline. Then, finite difference on the pipeline deflection at each lifting point was performed to obtain the bending moment of the pipeline, and then the lifting point force was derived. Furthermore, the analytical model was established for lifting and lowering-in. By the finite element model and on-site experiment, the analytical models were validated. Results indicated that: (1) taking the length of arched segment, the length of suspended segment, the maximum stress and the bending moment as comparison variables, the maximum errors were 5.56%, 5.96%, 5.35%, 7.36% between the sinking and lowering-in model and the finite element model, while were 8.79%, 4.27%, 8.68%, 8.72% between the sinking and lowering-in model and the on-site experiment; (2) the maximum errors between the lifting and lowering model and finite element model were 7.63%, 8.59%, 3.74%, 6.44%, 9.51% and 8.13%, considering the lifting force and pipeline stress in the vertical plane, the lifting force and pipeline stress in the horizontal plane, and the combined lifting force and combined stress as comparison parameters, and meanwhile the analytical results showed the overall agreement to numerical model at the trench-touched point and the ground-departed point, with the relative errors of 8.59% and 3.68% (in the vertical plane), 5.73% and 4.39% (in the horizontal plane), 6.85% and 4.12% (combined stress), respectively.

Reliability inverse analysis method of X80 pipeline parameter design is proposed. Considering the condition of normal and non-normal distribution for design variables, the inverse problem calculation theory of stochastic reliability is analyzed. Based on the first order second moment reliability theory, geometric algorithm is introduced to solve inverse problem. Convergence rate of checking point is accelerated by step length choice, and the corresponding calculation program about reliability inverse problem is developed by Matlab. Taking X80 pipeline of west-east gas project as an example, the results of reliability inverse problem for pipeline parameters are given and analyzed. Also, the example results show that the method is credible and has high precise. Therefore, the method can be applied in the X80 pipeline parameter design.

The analytical formulas of plastic limit load of X80 steel pipe elbow with non-uniform wall thickness leading by production error have been established on the basis of the force balance method. The influences of external diameter (D₀), rate of internal and external diameter (K), and curvature radius (R) on plastic limit load of pressurized elbow are studied. The analysis results indicate that the plastic limit load is equidirectional with the increase of the rate of internal and external diameter, and curvature radius. However, the curvature radius and external diameter have little effect on the limit load. In order to validate the accuracy of the analytical formulas, 3-D finite element model of pipe elbow has been built up. The comprehensive results show that the analytic solutions are in good accordance with the numerical solutions, which can be serviced as the foundation and reference of the calculation of pipe elbow plastic limit load in field engineering.