Abstract
The use of pipeline as a reliable, safe and cost-effective mode of transportation for hydrocarbon including crude oil, POLs, natural gas or for water, sewage transmission among other services, is well established in the industry. A pipeline, while traversing from the point of dispatch to point of receipt may have to cross obstructions like river, canal, railway line, road etc. Various methods including conventional trench and lay method or trenchless techniques like Jacking-Boring or Horizontal Directional Drilling (HDD) are used to cross such obstacles. The conventional trench and lay method may be restrictive due to its disruptive nature or its limitations in crossing rivers / large water-bodies. Similarly, conventional HDD has its inherent shortcomings with respect to geology of the sub-surface conditions which renders it unsuitable for many real-world river crossing scenarios, where the presence of gravel, cobbles or boulders in the sub-soil makes pipeline installation by Microtunneling & Pipe Jacking as the preferred method. Microtunneling involves installation of pipes, preferably concrete, below ground by jacking behind a remotely controlled, steerable, guided, articulated Microtunnel Boring Machine providing continuous support to the excavation face and the bored cavity / opening and uninterrupted removal of excavated spoils without requirement of any personnel entry into the tunnel. Microtunneling activity involves construction of Launch, Receipt and Intermediate Shafts, installation of Jacking Pipes employing suitable Guidance System followed by securely installing the pipeline carrying the hydrocarbon (or other fluid) within the installed tunnel.
The present case study discusses at length the crossing methodology selection of a 26″ crude oil pipeline of an operator across the Gangia River in Assam, India. The particular geology of the river bed will make any unsupported opening or hole made by HDD method prone to collapse from the surrounding boulders occupying the void, making Microtunneling as the method of choice for installation of pipeline across such rivers. The instances of use of Microtunneling for pipeline installation across the world is limited, lesser so in India, with the exception of Tista river crossing in West Bengal, East-West Gas Pipeline crossing Gauthami Godavari River in Andhra Pradesh or a few completed and ongoing projects in North-East India. The presence of gravels and boulders in the sub-soil strata through which the pipeline is proposed to be laid across Gangia River makes Microtunneling as the only possible choice of installation.
