Using the Unit Force Method to Analyze Thrust Acting on Anchor Blocks Caused by Thermal Expansion Displacement of X80 Tunnel Pipelines

Abstract

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, the results of thrust acting on anchor block of the X80 tunnel pipeline for a specific gas pipeline project are calculated and compared. The results show that the analytical results agree well with those determined by finite-element software, and the maximum relative error is only 2.9%. The parameter analysis of the thrust and displacement of anchor blocks is investigated, including the buried depth for anchored pipeline side, the pipeline–soil friction coefficient, the volume of anchor block, the block–soil friction coefficient, the soil reaction coefficient, and the buried depth of anchor block.