Introduction  Trenchless horizontal directional drilling is widely used in power cable line project to cross natural or artificial obstacles at present.Multiple cable protection tubes need to be laid successfully at one time in engineering applications. It is defined as multiple pipelines pulling crossing, and it is widely used because of it's excellent economic and environmental protection advantages. However, there is only the calculation method of single pipe pullback force of plastic pipe at present. This paper aims to study the calculation method of pullback force of multiple pipelines.

  Method  This paper was based on a 220 kV cable line project in the Pearl River Delta. This project used horizontal directional drilling to cross the national first-class waterway for twice at the same place, and most of the crossing stratum was plastic clay layer. The calculation method of single pipe pullback force was used for analysis in the project, and the change curve of pull back force was measured on site during the implementation.

  Result  The comparative analysis between theoretical calculation and measured results shows that: under the condition of plastic clay layer, the measured pullback force of multiple pipelines is 4～6 times that of single pipe with the same weight and envelope diameter. The straight-line pullback of pipelines is very important to reduce the pullback force and implementation risk.

  Conclusion  In this paper, the concept of multiple pipelines pulling and the calculation reference value of pulling force in trenchless horizontal directional drilling crossing project can provide a reference for the crossing design and construction of similar projects in the future.