Trenchless Construction Methods Explained: The Pipe Express
One method that combines the innovation of trenchless technology and utilizes a small degree of trenching is the pipe express method.
Innovation in trenchless methods of pipeline installation and rehabilitation is taking place on a regular basis. Researchers are always striving to find ways to make technology better and more affordable.
As a result, more and more organizations and municipalities are taking bold steps to implement this environment-friendly, cost-effective and long-lasting alternative to traditional open trenching. The crudeness associated with the construction of pipelines resulting in dug up roads, broken pipelines and traffic jams is quickly becoming a thing of the past.
However, some things die hard, and one such method that combines the innovation of trenchless technology and utilizes a small degree of trenching is the pipe express method.
The History of the Pipe Express Method
The pipe express method was first used in the Netherlands in November 2012 for installing a 48”, 1600 feet gas pipeline. The method was developed by Herrenknecht, and set new standards for installation of a pipeline over long distances. The method is semi-trenchless but consumes about 70% lesser ground space than open trenching.
It is suited best for near-surface pipeline installation and can install pipelines with diameters ranging from 900 mm to 1500 mm and distances up to 2000 meters. (Read Trenchless Pipeline Installation Methods and Their Pros and Cons.)
Other installations using the pipe express method include a 42” gas pipeline in Thailand in 2014, and a 48” water pipeline, 1036 meters long in Stockholm, Sweden in March of 2015. The interest in pipe express is growing particularly with the Trans Mountain Expansion Pipeline project in western Canada especially with challenging ground conditions and tight easements.
The Pipe Express Method
The pipe express method combines the use of the tunnel boring machine (TBM) and a compact trenching unit. A launch pit is dug at the point where the pipe will enter the soil and houses a pipe thruster and TBM. (Read How Tunnel Boring Machines Work.)
The trenching unit is attached to a buggy that makes a narrow trench (width approx. 40 cm) on the soil. The actual tunnel is below the trench and is excavated by the TBM. The excavated soil from the TBM is brought up by the trenching unit and is backfilled behind the machine as the installation progresses. The pipe thruster pushes the pipe as well as the TBM through the soil till the installation is complete and the unit exits at the receiving pit.
A bentonite unit helps lubricate the annular space between the pipe and the soil to reduce friction. A crane helps lower and position the pipes within the launch pit as excavation proceeds. Once the installation is complete the systems are disconnected and the trenching unit is lifted out. (Read Bentonite and the Use of Drilling Mud in Trenchless Projects.)
The entire process is remote controlled and guided by a trained operator.
Benefits of Pipe Express Method
- Minimal earthwork compared to open trenching.
- No need for lowering of groundwater except if required in the launch and receiving pits.
- Very beneficial in places where the water table is very near to the surface.
- Soil is removed directly and not displaced to install pipelines.
- Excavated soil is used for backfilling directly behind the machine as the installation progresses.
- The entire pipe installation is carried out in a single operation.
- About 1,000 meters of pipeline can be installed per day.
- Compact machinery is used that is easy to transport and install.
- The minimal disturbance of soil by this method makes it easier to convince landowners to allow installation through their property.
- Economically beneficial compared to open trenching.
- The entire process is environmentally friendly and is most suited for locations that are sensitive.
Limitations of Pipe Express Method
- This method can only be used in soft or heterogeneous soil such as clay, silt, loam, sand, and gravel.
- The installation diameter is limited from 900 mm to 1500 mm.
- Only steel pipes can be used for installation since clamping and thrust force is applied on the pipe.
- Standard installation depth is 2.5 m with special design installation depth available up to 4.5 m.
- Cold bent steel pipelines cannot be used to change direction as in the case of open trenching.
- The pipe express route has to follow the minimum bending radius of the steel pipe.
The pipe express method is especially useful in places where pipe installation has special requirements such as in nature conservation sites, unstable soil, and aquifers. Using traditional methods incurs high costs especially when the installation is near the surface and open. Pipe express significantly reduces the cost of execution and land rehabilitation.
The one-pass pipeline installation and minimal use of conventional construction equipment help reduce exhausts, emissions and noise pollution, thereby effectively reducing the carbon footprint of the project. (Read Understanding Construction Emissions: What’s Causing Greenhouse Gases & How We Can Improve.)