Subsurface Utility Engineering: Supporting Design and Managing Construction Risk Introduction

Our public rights-of-way (ROW) serve the public through the transportation of people and goods while also housing critical utilities. Both public and private utilities are routed both above and belowground. Underground utilities form the invisible backbone of modern civilization, yet they represent one of the greatest risks to construction projects. With millions of miles of buried infrastructure across the country, the complexity continues to grow exponentially. The uncertainty in the positions of these subsurface utilities results in risk for the designers, contractors, and owners operating in the ROW.

One way to mitigate the risk of subsurface uncertainty is through the application of Subsurface Utility Engineering (SUE). SUE is defined as “The specialty practice of civil engineering’s Utility Engineering branch that includes the investigation, analysis, judgment, and documentation of existing Utility networks.”

The critical elements of SUE are the quality levels; which can be summarized as (in order of decreasing uncertainty):

• Quality Level D: Based on utility owner records/information
• Quality Level C: Based on correlation of owner records to visual observations
• Quality Level B: Based on geophysical exploration and judgement
• Quality Level A: Based on physical exposure of utility

The application of SUE adds value specifically in design support and risk mitigation. An engineer can only design a project based on the subsurface understanding they have. Reduction in the uncertainty of that information improves the design and limits the risk of costly impacts during construction. The contractor physically encounters the utility conflicts but the risk often lies with the owner.

SUE as a Design Support Tool

Subsurface utility conflicts are unavoidable for most projects including subsurface work, especially in urban environments. Designers have three basic options when dealing with a conflict; 1) Change the design; 2) Move the utility; or 3) Mitigate the impact to the utility. None of these can be effectively executed without adequate knowledge of the subsurface.

The balance between expending effort and gaining the maximum benefit from the data is the key to efficient SUE services.

Example of SUE execution and changes in design resulting from the findings of various SUE quality levels:

• A traffic signal foundation was designed based on SUE QL-D data in an urban environment
• Upon execution of geophysical exploration and achievement of SUE QL-B utility designations, the locations of reported utilities necessitated a re-design. The foundation was moved and the design revised.
• Upon execution of physical exposure and achievement of SUE QL-A utility positions, the horizontal distance required for the foundation was confirmed; However, a previously unknown utility was encountered at depth.
• Utility relocation was considered, as well as alternative foundation design and the foundation location was revised several times eventually resulting in a constructable design.

Engineers love “knowns” and can struggle with “un-knowns.” The benefits of applying SUE to a project range from improved constructability, fewer redesigns, and better coordination all the way to saving lives by avoiding combustible utility strikes.

Risk Management through SUE

The contracting world is most often based on low-bid selection for projects. As such, contractors must do their best to submit a project price that meets the scope of the design; no more, no less. The risk associated with subsurface uncertainty is either retained by the owner or pushed to the contractor (and paid for by the owner). For this reason, the more subsurface uncertainty is reduced in design the lower the risk during construction.

What are the risks associated with subsurface uncertainty?

• Utility conflicts discovered in the field cause schedule and budget overruns. The nature of the conflict and the type of utility affect the impact which can be several months and millions of dollars. It is reported that $15B is spent on utility strikes in the U.S. annually (300+ utility strikes per day).
• Health and safety risks include worker harm with natural gas, electrical, or other utilities during excavation as well as health impacts to users such as contamination or loss of water service.
• Inflated contractor bids and contingency costs associated with acceptance of the risk by the contractor.

Uncertainty is risk and it takes investment to mitigate that risk. The investment can be up-front in the form of SUE services or on the back-end during construction. Studies have shown that the application of SUE services can have a return on investment on the order of 4:1 to over 20:1. The “best” SUE projects result in no utility conflicts during construction and are forgotten about. The best advocates for SUE services are those professionals who have experienced what can happen when SUE is not utilized and things really go sideways in the field.

Best Practices for Using SUE Strategically

Sue services can be immensely beneficial to a project, but they are not cheap. It is critically important follow best-practices in the application of SUE in order maximize its benefits.

When is the appropriate time to engage SUE services in a project? The short-answer is sooner rather than later. The quality level of SUE applied may be planned within the overall project schedule. For example, QL-D is appropriate during preliminary design; QL-B may be appropriate between preliminary design and detailed design; and QL-A may be appropriate between detailed and final design. Timing of SUE implementation in project phases

Education and communication of SUE findings is critical in proper application. The use of conflict matrices and integrated SUE data in design workflows enhances the use of the data. Stake holders in a project should have a basic understanding of the SUE quality levels and how this information is disseminated within a project. Under-utilization and miss-interpretation of SUE data can be wasteful and dangerous.

SUE providers should be engaged in projects and working collaboratively with utility owners and design teams. Utility information is often “living” and changes throughout the duration of a project as more and better data are obtained. Designers can develop and identify SUE needs with the SUE providers and interpret SUE results through ongoing collaboration.

Subsurface utility risk is present in essentially every earthworks project in the ROW. Proper identification and embedment of SUE in QA/QC and project risk planning supports safe and efficient project execution. The SUE information is also available for future projects and can be compiled over time to reduce risk in perpetuity.

Conclusion

SUE reduces subsurface uncertainty and promotes accurate design and efficient construction. The proper application of SUE services supports safe, cost-effective, and quality projects that owners, users, and stake holders are proud of. Mitigation of construction risk through SUE can control budget overruns and ensure timely execution of projects by reducing the “surprises” encountered during excavation.

Studies show that 80% of utility damage is preventable with the proper use of SUE. It is up to the project owners to elect to manage their risk by applying SUE services when and where appropriate in their civil infrastructure projects. It is up to the SUE and design professionals to effectively collaborate and apply SUE maximize its benefits for the projects and stake holders. Together, the collective industry can reduce project costs, delays, and public impact through SUE.