Many utility contractors are now utilizing trenchless technology as their main method of installation for services such as water, sewer or gas utility pipelines, or are at least familiar with the techniques used. Trenchless technology has changed the face of the construction industry by eliminating the biggest problems faced by the traditional trenching or open cut method – dug up roads, road blocks, traffic congestion and a larger carbon footprint.
That, however, does not mean that trenchless technology is flawless; it has its share of challenges that need to be addressed. Since trenchless construction methods work below the surface of the earth, some problems may come as a surprise even to an experienced contractor.
Risks Associated with Trenchless Projects
Risks are an integral part of any construction project, but managing those risks can make all the difference. Identifying potential risks during the planning and design phase can help eliminate or at least reduce the risks to a certain extent. However, unexpected risks can occur and contingency plans should be put in place to take the best recourse. Some risks faced by trenchless projects include: a failed borehole, environmental issues such as frac-out, damage to other utilities and safety issues.
Of these, a failed borehole is a contractor’s biggest nightmare, resulting in heavy financial losses. A failed borehole can be caused by loss in drilling fluid circulation, stubborn obstructions, hydrolock, problems with line and grade, collapse of borehole and damage to product pipe.
Below are listed the top 5 challenges that a trenchless construction project is most likely to face.
Locating and Exposing Utilities
Before beginning a project, the contractor should call the local one-call center or Dig Safe to counter the biggest challenge he will face in the project: locating existing underground utilities. While these agencies will not give you the exact depth of the utility, they can give an approximate line along which it is installed.
Thereafter it is the contractor’s responsibility to mark and expose the utilities at regular intervals. Many states do not require sewer and water utility owners to be members of the one-call system, hence physical investigation should be done to look for manholes, drops, meters, storm drain outlets and other utility structures that may lie along the route. The drill path should be designed so as to steer clear of all utilities.
Obtaining a Comprehensive Geotechnical Investigation Report
The importance of an exhaustive geotechnical investigation cannot be overstated. Every report is unique to the site, client and type of project and is non-transferable to another project, even if in the same location. Contractors should ensure that the geotechnical report covers as much detail as it can about surface and subsurface conditions along the route of the pipeline project.
Yet, even a geotechnical report can have moderate to significant variation regarding subsurface conditions, as the sampling is conducted at specific intervals along the pipe route. (For more, read Why a Detailed Geotechnical Report Means Success for Your Trenchless Project.)
Incorrect Installation Technique
Sometimes contractors are faced with the dilemma of choosing the right trenchless installation method. Soil type and density has a significant impact on the feasibility of a project, as it will determine the method to be adopted. For example, for gravelly soil, using horizontal directional drilling (HDD) can lead to substantial cost overruns and even failure of the project. Also, the contractor has to be prepared to face any unforeseen subsurface condition such as soil variation, groundwater or encountering an undocumented utility. For this he should have an arsenal with contingency plans, methods and equipment to tackle the situation at hand.
Finding a good drill operator and tracking the drill bit is yet another challenge that a contractor has to face. Sensors are installed in the drill head, yet before beginning to drill, checking for sources of interference is a good idea. Walking the planned path with the drill operator by turning on the tracking receiver and leaving the transmitter off to look for variation in signal strength and unusual readings and marking the spots is recommended by the Association of Equipment Manufacturers (AEM).
Some sources of interference are traffic signal pads, cathodic protection currents, underground metal tanks, steel pipes and buried cables that transmit high frequency signals. Communication between the drill operator and the operator handling the tracking equipment is essential. If any inconsistencies are encountered, it is best to stop the drilling and rectify the problem before resuming.
The Occupational Safety and Health Administration (OSHA) has stipulated rules with regards to workers' safety at the construction site. Workers can be exposed to a number of safety hazards, and the contractor should ensure that the workers are attired with appropriate safety gear such as safety shoes, goggles, gloves and helmets. Proper training prior to beginning work at the site can help minimize human error.
For example, using a pipe wrench instead of tongs to separate the pipe string can lead to serious or even fatal injuries, or handling coiled plastic pipe without proper precautions can cause the pipe to uncoil violently. It is the contractor’s responsibility to enforce safety rules on site, as workers are prone to prefer comfort to safety precautions. (For more on safety, see Trenchless Operations Safety Do’s and Don’ts.)