Trenchless technology will soon be the leading choice for pipeline construction and rehabilitation projects. While open-cut methods have not become obsolete, they have been largely replaced by trenchless methods that are faster and cost-effective in the longer run.
The world over, researchers as well as contractors are comparing the benefits of open-cut vs. trenchless methods and are finding that trenchless methods do have immediate and long term benefits. For one, the indirect and social inconvenience costs associated with open-cut construction is largely eliminated in trenchless methods.
However, one big challenge remains as to which method is most suitable for a particular project.
Factors Influencing Method Selection
There are many different methods of trenchless technology that can be chosen for a particular project. Every method is unique and has its sets of benefits and challenges. Knowing how to select the appropriate method can make a lot of difference in terms of time, cost, and reputation to a contractor.
The question, therefore, arises as to how to choose the best trenchless method for your particular project. (Read also: How to Best Prepare for a Successful Trenchless Construction Project.)
There are many factors that influence the selection of a particular method for both construction and rehabilitation projects. Factors that influence the selection of a trenchless rehabilitation method include conditions on the ground surface, conditions below the surface, present condition of the pipe, what needs to be done to the pipe (whether upgrading pipe capacity, replacing the pipe or renewing the pipe), and cost.
Factors that influence the selection of a trenchless construction method include application, factor uncovered by the geotechnical report, depth of installation, shafts, drive length, type of pipe material, the diameter of the pipe, and cost.
Choosing the Right Method
Just like every other technology, there is no “one method solves all” trenchless method. Contractors have to make sure that they select the method most suitable for the project at hand.
Urbanization is driving the trenchless industry but often chief factors for method selection are overlooked. Improper methods can lead to serious issues such as damage to existing pipelines, and settlement and heaving of ground surface causing damage to surrounding structures.
Trenchless methods are mostly preferred over the open-cut method when:
- Environmentally sensitive issues arise.
- Road digging can lead to bottlenecks causing traffic disruption.
- Pipes have to be installed at great depths requiring removal of large amounts of earth.
- It is necessary to maintain a bypass flow.
- Dewatering is required due to the presence of excess groundwater.
- There are right-of-way issues.
Influencing Factors
Here we will take a brief look at the various factors that play a role in the selection of a trenchless pipeline installation method. We know that trenchless installation or construction methods include horizontal directional drilling (HDD), pipe jacking, horizontal auger boring (HAB), microtunneling, pipe ramming, and utility tunneling.
HDD is limited to pressure pipeline applications; microtunneling is limited to gravity pipeline applications, while HAB and pipe jacking can be used for both pressure and gravity pipeline applications. (Read also: Microtunelling vs HDD: Understanding the Differences.)
The factors that govern the selection of a method largely depend on the geological makeup of the subsurface strata. In some cases, more than one method can also be proposed and the best one is selected based on the availability of equipment and skillful team, budget, and sustainability principles.
Picking up a random method because it fits the budget and convenience of a contractor or client can lead to undesirable results. The following are some parameters that are important in selecting an appropriate and specific method for a particular project.
Geotechnical Considerations
Every project has a unique site and soil condition which are very important in determining the most appropriate trenchless method. Geotechnical investigation is carried out in two parts—surface and subsurface investigation.
The surface investigation gives information about the topography of the area, its grade, elevation, test pit and borehole locations, environmentally sensitive areas, and structures along the proposed route.
The subsurface investigation will give the information about existing underground utility structures in the area, type of soil, and distribution of soil strata, water table, and depth of bedrock.
For example: for soft to very soft soils and organic deposits, HAB, HDD and microtunneling are all suitable; for medium to dense sands below the water table, HDD and microtunneling are suitable while HAB and pipe jacking are not feasible.
Installation Depth
Soil conditions can restrict the application of a particular method if the required driving force is higher than the capacity. The maximum depth of installation using HDD is restricted to 160 feet owing to the absence of entrance and exit shafts and limitation of the tracking system. Other methods can be applied at any depth as shafts are dug at both ends to the required depth.
Drive Length
If the drive length is more, the driving force required for installation also increases. The recommended drive length for different trenchless construction methods:
HDD – 12 to 1800 meters;
Microtunneling – 22 to 225 meters;
HAB – 12 to 150 meters;
Pipe Jacking – 150 to 305 meters.
Pipe Diameter
The recommended diameter for different trenchless construction methods:
HDD – 12 to 48 inches
HAB – 12 to 48 inches
Pipe Jacking – 12 to 168 inches
Microtunneling – 12 to 168 inches
Pipe Ramming – 12 to 168 inches
Pipe Material
Different trenchless methods can handle different pipe materials such as given below. (Read also: The Lifespan of Steel, Clay, Plastic and Composite Pipes.)
HDD – High-density polyethylene (HDPE); steel; polyvinyl chloride (PVC); vitrified clay pipe (VCP); ductile iron pipe (DIP); fiber-reinforced mortar pipe
HAB – Steel
Pipe Jacking – Steel; Fiber-reinforced mortar pipe
Microtunneling – High-density polyethylene (HDPE); Steel; Polyvinyl chloride (PVC); Vitrified clay pipe (VCP); Ductile iron pipe (DIP); Fiber-reinforced mortar pipe
Pipe Ramming – Steel
Is There a Calculator to Determine the Right Method?
That’s a question that most trenchless contractors and even clients ask themselves. We have been asked often about which method is most suitable for a particular project. Keeping that in mind, our experts are in the process of designing and launching a “Trenchless Method Calculator” that will help you do just that.
After much research and deliberation, our experts have come to the conclusion that there are few key parameters that largely determine the type of method most suitable for a particular project. A few of those parameters have been mentioned above. We believe this calculator will help you select the right method for your project.
If you are interested, you can try out the calculator soon. All you have to do is to fill in this form. As soon as the calculator is live, you will receive a notification. Be the first to try.
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