Pipe installation of pressure pipes systems is one of the largest projects in today’s construction industry. It involves putting underground a great deal of steel pipes that are used as conduits for water and other liquids, but more often these days to carry sewage.
The pressure pipe systems can be used to bring waste from remote places where it is difficult to build conventional sewers lines. The most common use of the pressure pipe systems is in transporting sewage from septage lagoons, waste stabilization ponds and other manmade wastewater treatment equipment.
Where To Use Pressure Pipe Systems
Pressure pipes are now being used in rural areas where it is not possible to deliver clean water and sewer lines due to distance and cost. It is the most preferred method of bringing wastewater from septic tanks in rural areas, waste stabilization ponds, municipal solid waste (MSW) landfill leachate collection systems and other remote locations.
Pressure pipe installation using the HDD method offers many advantages over conventional sewer line installations: They are considerably faster to install (up to 10 times faster) than a conventional sewer installation.
The pipe is placed much less expensively and in less time than conventional methods. They cover long distances on flat land without significant grades or high lateral pressure requirements. They can be installed at depths of up to a mile (1,600 feet) or more with the use of an hdd drilling machine and pipe.
It reduces the environmental impact of a sewer installation by not disturbing more resources than necessary. It saves money because there is no need for large excavations, connection trenches, or pump stations. It eliminates costly construction over environmentally sensitive areas such as wetlands or streams, and they are easier to install in rocky areas and frozen ground.
With the advancement of horizontal directional drilling technology, a high-pressure pipe system is now possible and can be used to carry wastewater at less cost and with fewer negative environmental effects.
Horizontal directional drilling allows large volumes of contaminated fluids such as municipal, industrial and mining waste to be piped from remote or inaccessible areas in a variety of conditions, including difficult geology.
Horizontal Directional Drilling Method
The “pressure pipe” refers to a construction in which the pressure of sewage is changed by a pipeline without disturbance. It can be used in sewerage, such as closed circuit treatment systems and open-circuit treatment systems. Moreover, it is applicable to conveyance of sludge or treated water from wastewater treatment plants, or for use on an isolated island.
The pressure pipe consists of a large-diameter, high-pressure pipe that is installed from the center of the sewage outflow to a pump or treatment plant for pressure change; and a small-diameter low-pressure pipe that is connected to this high-pressure side and connects downstream branches (such as horizontal direction). Horizontal directional drilling (HDD) is the most effective means for installing this kind of pipeline.
- How does it work?
Steel pipe that is used as a sewer conveyance pipe consists of a standard schedule 40 steel pipe with the inside diameter varying from 4 to 24 inches or more, according to the requirements of the project. The length of each piece varies depending on the required lengths of the pipes. The pipe diameter and pressure that HDD can handle are more than enough for sewage conveyance, so there is no need to make multiple boreholes and use large-diameter pipes.
In order to make the pipe work efficiently, it must be joined end-to-end in a series of pipe joints with a mechanical interlock that allows for movement between the sections under pressure while providing an airtight seal when pressurized. The bonded lengths are then buried using an hdd drilling machine.
The installation of pressure pipes are less disruptive to the surroundings, avoiding long trenches and environmental damage caused by open-trench construction. This approach minimizes impacts on roads, traffic congestion and surface structures compared with conventional installation of sewer systems.
- What are the advantages of using the HDD method for installing pressure pipes?
It reduces the environmental impact of a sewer installation by not disturbing more resources than necessary. It saves money because there is no need for large excavations, connection trenches, or pump stations and it eliminates costly construction over environmentally sensitive areas such as wetlands or streams.
Pressure pipes can be installed in conditions that are inaccessible to conventional methods of installation. This includes installations over open water bodies, rocks and frozen ground.
The cutting head attaches and supports the pipe as it is positioned through the borehole. When the pipe has been installed completely across the stream the cutter assembly is removed and a closing cap welded on for an immediate water tight seal across the stream channel.
The cost per linear foot for installation varies depending on geologic conditions, openings encountered, distances between the surface and the crossing points. The cost of trenchless sewer installation is typically 10% to 20% less than conventional methods such as open-trench construction with regard to costs for materials, removal of dirt, equipment rental, labor wages and supervision.
The extended lengths allow project designers to install another cross-section or interconnect another branch of the sewer network without having to drive open trenches, saving time and money.
- What are the challenges?
Contractors considering HHD as an installation option should be mindful of geological factors along the planned route. The HDD method faces distinct problems while working with shallow bedrock and sandy soils.
For example, a sewer forcemain was extended across a busy public park and driving range in sandy soils. The contractor had many blow-outs during the first stage of the HDD procedure because the original pilot hole was too close to the surface.
The drill head deviated from the intended path due to the unconsolidated sandy soil in the area being pushed upward. To avoid further blow-outs, the idea was to back up and dig a little deeper in the sandy soil sections.
Drilling through shallow bedrock poses its own set of difficulties. Drilling heads may require unique alloy materials, and shallow angle bedrock strata might create difficult drill defection scenarios away from the specified path.
HHD methods are also further hampered by congested utility corridors and/or limited utility right-of-ways (ROW). Thus, the design engineer is strongly urged to use subsurface utility engineering services to perform quality designation of utilities that cross the intended path.
Takeaway
In situations where traditional cut-cover installation procedures are required, directional drilling may be a realistic option to consider for installing pressure pipes. In addition to speeding up the project schedule, this building method can reduce ground disturbance and traffic impacts, which could help with project permitting.
When it comes to water distribution and sewer force main installation, HDD is becoming more cost-effective than traditional approaches, and is expected to grow in the upcoming years.
