Direct Pipe ®: Latest innovation in pipeline construction - technology and references
Nov 10, 2008
Various methods have so far been applied for crossing works in order to build steel or polyethylene pipelines as pressure lines. Pipe jacking and segmental lining allow for the construction of protective tunnels with subsequent insertion of the pipe string. The HDD method, in contrast, includes the construction of a pilot bore prior to pipe pull-in. Recent developments such as the Easy Pipe method comprise jacking processes -- where tight connection interim steel pipes are pushed towards the target shaft, coupled to a pipeline and then pulled back together. All these methods include a two- or multi-step pipe installation process. The multilevelness of these methods and pertinent aspects such as costs and project duration led to the development of the DIRECT PIPE® method: Steel or polyethylene pipes can now for the first time be jacked efficiently and fast in one operation process.
The tunnel face is slurry-supported using a bentonite suspension. The excavated material is removed via a slurry circuit with separation plant in order to separate the spoil from the slurry liquid before feed pumps transport the liquid back to the tunnel face. The micromachine is controlled from the operating container. A gyro compass is used for machine surveying. The micromachine, pipes and connection pipes are designed conically, which increases the annular gap between the machine or pipe sleeve and the surrounding ground. Bentonite is injected into the annular gap for lubrication from the cutting-wheel assembly. In addition, a lubrication ring is mounted in the transition area between the connection pipe and the product pipeline, where most of the bentonite is added, in order to reduce the friction between the pipeline and the ground to a minimum. In contrast to pipe jacking, a Herrenknecht Pipe Thruster is set up in the launch pit instead of a jacking frame. The Pipe Thruster clamps the pipeline on the outside and pushes the pipes as well as the microtunnelling machine strokewise forward with its thrust cylinders.
In the rear of the Pipe Thruster, a prefabricated and tested product pipeline is positioned on pulley blocks ready to be thrust forward. Different from pipe jacking or microtunnelling, the DIRECT PIPE® method allows for an installation of the slurry circuit from the start of the project not requiring a delayed installation and successive extension of the circuit: The slurry and pump system is operated parallel to pipe jacking along the entire drive length.
Due to this site configuration, the product pipeline can be installed in one step. The direct installation of the pipeline allows for continuous drill-hole support preventing hole collapse. The DIRECT PIPE ® site configuration also allows for a basic launch and target shaft design. It is only necessary to provide a launch seal and firm foundation for the Pipe Thruster on the launch side in order to transmit the thrust forces to the soil. Upon arrival in the target shaft, only the TBM and the connection pipes have to be disassembled; the installation of the product pipeline in the ground is then already completed. Feed and slurry lines as well as control, data and power cables are led through the pipeline on special roller assemblies; they can be easily removed from the pipeline using a rope winch.
- One-step jacking method, i.e. the product pipeline is pushed into the ground in one step, in contrast to all common methods, which have so far been applied
- Permanent drill-hole support in order to prevent a drill-hole collapse, advantage over HDD
- Cutting wheel and cutting tools of the microtunnelling machine can be adapted to any geological conditions, which is particularly beneficial over HDD
- Minimum space required, only on the launch side: Advantage over other methods, which either require considerable storage space on the launch side (pipe jacking / segmental lining), which require considerable space in order to install the product pipeline on the target side (HDD) or which require space on both sides (Easy Pipe)
- Minimum slurry volume required due to the small overcut
- High performance rates - due to the deployment of the Pipe Thruster and the possibility to install and test entire pipe sections
- The microtunnelling machine, which is equipped with U.N.S. navigation technology and a north-seeking gyro compass, guarantees high-precision target control
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