Trenchless Delivery Methods – Part I

By Arvid Veidmark III, President at SSC Underground

Trenchless technology is a rapidly growing sector of the construction and civil engineering industry, but what exactly does it entail and what are its benefits? This type of subsurface construction work refers to a family of construction techniques for installing or rehabilitating underground infrastructure with minimal disruption to the surface traffic, businesses, and community.

The term, trenchless technology, also includes the technologies for vacuum excavating, vacuum potholing, inspection, leak location, and leak detection with minimized disturbance and excavation from the ground surface. 

First, let’s deep dive into all the important considerations to be aware of with every project. Then, in Part II, we will provide the main types of alternative trenchless delivery methods, along with their best use recommendations with pros and cons for each.

Considerations

The first step in determining which trenchless delivery method will best suit your project’s needs is to fully understand all the project design considerations. The following items will significantly impact this decision, so you need to ensure you have a trusted partner that won’t overlook anything important.

Owner Requirements & Location

The initial step should always be to review the property owner’s requirements. Then, the location is a critical factor to take into account. This includes determining whether it is in a residential, urban, or rural area, but also it will help answer questions such as will more of an easement be required to gain the proper access?

Soil Condition

Obtaining a geotechnical report is something you do not want to skip. This will not only define the soil condition to make educated decisions about which trenchless method will be best, but it will also uncover all the soil types so there will be no costly surprises. In fact, ordering a geotechnical report can actually lead to construction cost savings. In analyzing the soil condition, it should be confirmed that the test holes are 5-feet below the designed bore path.

Utilities

Another crucial consideration of the project is knowing where any existing utility conflicts may be and whether they are adequately marked in the exact location. All existing utilities need to be potholed prior to the 60% design stage to ensure the window for trenchless methods is clear. Ideally, the project engineer should be potholing where utilities are early on. However, if you partner with a trenchless expert that also offers vacuum excavating and utility potholing services, you can rest assured this will be completed in an accurate and timely manner.

Casing Size

The size of the casing needed to ensure there is adequate room is dependent on the type of utility being installed. Some examples include water/forced main, gravity sewer, dry utility, and gas line. Moreover, you will need to specify the product type and pipe such as ductile iron pipe (DIP), reinforce concrete pipe (RCP), polyvinyl chloride (PVC), steel, and high-density polyethylene (HDPE). The final consideration is the size of the utility line, keeping in mind the largest OD at the bell – not just the ID of the line.

Depth/Length of Bore

The depth of the bore will drive the requirements for the bore pit and shoring. For instance, over 20’ deep will require engineered shoring. The ideal bore pit size is 40’ x 14’; however, if that is not possible, hand tunneling would provide the most flexibility to shrink the pit as less equipment is involved.

In determining the length of the bore, evaluating what is being crossed and the Right of Way requirements is important. The length can range greatly from 20’ to 1,000+’, which is critical to understand when it comes to selecting the proper method.

A couple of other terms to be aware of are shore boxes, which are most commonly used, and slide rails which are necessary when dealing with very deep pits and in certain soil conditions. A slide rail is dependent upon larger equipment to build and install, while shore boxes can be built with standard equipment on-site to provide flexibility with size.

Setup Conditions

Going back to the main theme of location, take it a step further and understand what the bore is being installed under. Is it a major interstate? Railroad tracks would present the most regulations, while waterways may be the most dangerous. Also, it is importantly to proactively know how much space is available for setup. The recommended amount in order to keep safety at the forefront is at least 100’ x 100’.

Time Frame

This final main consideration is to be determined by the most optimal method that is selected. For instance, hand tunneling may provide the most control but may take the longest, whereas auger boring may be faster but offers less control. Stay tuned for the Part II blog post to compare the pros and cons of the many options.

When it comes to the lucrative practice of utilizing trenchless technology methods, or construction techniques for underground infrastructure with minimal disruption to the surface, there are a myriad of considerations to take into account that will greatly impact your project’s success.

Remember, it is an industry best practice to order a comprehensive geotechnical report to help determine the best trenchless delivery method based on exact soil conditions and obtain the most accurate pricing for the job. Keep in mind, if you simply award the lowest bid, you can also expect the lowest quality and perhaps not even the right solution. Another pro tip is to partner with a trusted expert with local, targeted knowledge and experience.