12 AUGUST 2022 WorldWide Drilling Resource® The Best of Both Worlds with the Direct Pipe Method® Adapted from Information by Herrenknecht and Laney Directional Drilling Horizontal directional drilling and microtunnelling are well-established means of installing pipelines all over the world. The Direct Pipe® method incorporates the best aspects of these two tried-and-true techniques. It was developed by Herrenknecht to create a one-step pipe jacking process; provide an efficient alternative to existing methods; reduce jobsite infrastructure surfaces; and minimize geological risks such as borehole collapse. In 2007, a culvert installation called the Rhine crossing near Worms, Germany, was the first project to employ the Direct Pipe method. Expectations were high, and impressive results exceeded optimism surrounding the strategy as performance rates allowed over 1500 feet of pipe to be quickly set in place. In 2010, the method made its debut in the U.S. for a gas line project under a highway in Arcadia, Florida. Approximately 705 feet of pipe was installed safely and swiftly in three days. Worldwide demand for trenchless pipeline installations continues to grow for a variety of applications such as water transport, communications, and utility lines. The Direct Pipe method offers significant benefits for these projects. When using this method, the entire setup is located on one side of the lake, river, highway, or other environmentally-sensitive area under which pipe is to be installed. Direct Pipe installations therefore use less labor and equipment; cause less environmental disruption; and can be implemented in more densely-populated areas. In the Direct Pipe Method, a microtunnelling machine is mounted in front of the pipeline. The cutting wheel can be equipped with cutting tools adapted to specific geological conditions. Larger boulders, hard rock, and soft soils can all be crossed. Two to three angular steel connection pipes are installed between the pipeline and machine for control. The Pipe Thruster, which is a thrust unit operating from the launch pit, clamps the pipeline on the outside and pushes the machine and pipeline into the ground. The push force is transferred to the pipeline through the clamping unit and then to the machine’s cutterhead. The microtunnelling machine pumps excavated material through a slurry circuit inside the prefabricated pipeline to a separation plant located aboveground. During excavation, the tunnel face can be consistently and safely controlled using slurry-supported technology, even in heterogeneous, water-permeable soils. Guidance systems can be used to manage uphill and downhill slopes, as well as curved drives along the alignment. Once excavation is complete, the microtunnelling machine is recovered in segments of about ten feet. In a final step, the supply and discharge lines are removed from the pipeline. The Direct Pipe method significantly lowers pressure on the surrounding subsurface formation and greatly reduces the risk of hydraulic fracture and inadvertent returns. This makes it ideal for installations in sensitive areas where traditional trenching techniques such as digging and burying pipe are not practical. By combining valuable aspects of two renowned methods for installing pipelines, Direct Pipe is a unique solution which offers theoretical advantages in certain conditions, along with practical results. This technique has continued to prove its worth for more than a decade in international projects. DIR Photo courtesy of Herrenknecht.
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