Backtow technique of underwater optical cable together with pipeline in horzontal directional drilling in rocky area

The geological conditions along the eastern section of the Second West-to-East Gas Pipeline are complex. To solve the technical issues in HDD, the backtow technique of underwater optical cables together with main pipeline was adopted referring to the current crossing situation in Jinjiang HDD Project of the Second West-to-East Gas Pipeline. This paper, based on the project case, describes the selection of underwater optical cables, fixing mode of optical cables, borehole quality control of directional drilling, strain release and winding, risk prediction and prevention, etc, and analyzes the stress condition of optical cables in construction, and its designed backtow force is 6.894 kN, only 1.19% of that of the main pipeline. This technique is the first successful application in China, which effectively shortens the construction period up to 20%, and saves construction cost by 80% compared to traditional crossing with steel casing. It is considered that this technology can be effectively applied in crossing complex geological structures like rock, with good economical and social benefits and high promotion value.