The outcome of building an underwater crossing using horizontal directional drilling method is a pipeline run through a horizontal hole. For successful pulling of a pipeline a hole should be prepared with design parameters suitable for smooth pulling of the pipeline on inclined and horizontal sections of the hole.
The review of pipeline pulling jobs on different underwater crossings involving pipes with the outside diameter of 530 mm to 1220 mm has shown that problems are most likely to be encountered in the following curved sections of the HDD hole: shoulders in the intervals of interface between the soils having different strength; intervals of unconsolidated soils and loose clay-bearing soils caving; intervals in which high plasticity clays are squeezed into the hole; intervals in which large rock inclusions are accumulated on the lower wall of the hole. Voids on the lower wall of the hole or partial filling of the hole with soil causes additional bending moments in the pipeline. Local dogleg sections occur in the hole as a result of a failure to observe good drilling practices or the use of technologies which are incompatible with the existing geotechnical conditions of drilling.
For the avoidance of drilling problems and prevention of a loss of the crossing hole and the pipeline as a consequence of local dogleg sections made during the drilling, the condition of underwater pipeline crossing hole should be subject to stringent requirements, and its geometry and profile should be closely monitored before the pipeline pulling is attempted. To this end we have reviewed the available data related to the pulling of pipelines through underwater crossings build by HDD method, possible changes of the hole path, and effects of the hole geometry on the possibility of pulling the pipeline from the standpoint of the drilling rig pull capacity, and stress-related properties and strength of the pipeline. As a result of this study, prerequisite conditions for safe pulling of the pipeline through a HDD hole of an underwater crossing in case of a change in its path due to contamination with cuttings, or on the interface of soils with different strength properties were determined.
References
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2. Vafin D.R., Sapsay A.N., Shatalov D.A., Technical and economic limits to the application of the horizontal direction drilling method in the construction of underwater transitions of main pipelines (In Russ.), Nauka i tehnologii truboprovodnogo transporta nefti i nefteproduktov, 2017, V. 7, no. 3, pp. 66–73.
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