Managing Project-related Risks
Subsurface utility engineering is an engineering process that locates, assesses and manages the risks associated with underground utilities throughout the lifecycle of construction projects.
The American Society of Civil Engineers has published guidelines for the application of SUE. The "Standard Guideline for the Collection and Depiction of Existing Subsurface Utility Data" describes the roles and responsibilities, methodology and defining characteristics of SUE work.
The benefits of SUE are many, including:
- Reduction in conflicts between existing utilities and construction activities.
- Increased jobsite safety.
- Increased savings for both cost and schedule.
Beyond these, application of SUE applies a standardized quality levels to project plans, allowing designers to better communicate uncertainties that exist related to subsurface utilities.
Highway plans typically contain disclaimers as to the quality of the utility information. The use of the designated quality levels in the SUE process allows designers to certify, on the plans, that a certain level of accuracy and comprehensiveness has been provided. The final project plan set or CAD file may contain any or all of the four SUE quality levels, described here from low to high accuracy.
Quality Level D information comes solely from existing utility records.
It may provide an overall "feel" for the congestion of utilities, but it is often highly limited in terms of comprehensiveness and accuracy. Its usefulness should be confined to project planning and route selection activities.
Quality Level C involves surveying visible above-ground utility facilities, such as manholes, valve boxes, and posts, and correlating this information with existing utility records.
When using this information, it is not unusual to find that many underground utilities have been omitted or erroneously plotted. Therefore, its usefulness should be confined to rural projects where utilities are not prevalent, or are not too expensive to repair or relocate.
Quality Level B involves the use of subsurface geophysical techniques to determine the existence and horizontal position of underground utilities. This activity is called designating.
Through designating, the horizontal data collected allows for the development of more accurate two-dimensional maps. This data is usually sufficient to accomplish preliminary engineering goals.
Decisions can be made on where to place storm drainage systems, footers, foundations and other design features in order to avoid conflicts with existing utilities. Slight adjustments in the design can produce substantial cost savings by eliminating utility relocations.
Quality Level A involves the use of non-destructive digging equipment at critical points to determine the precise horizontal and vertical position of underground utilities, as well as the type, size, condition, material and other characteristics. This activity is called locating.
It is the highest level presently available. When surveyed and mapped, precise plan and profile information are available for use in making final design decisions.
By knowing exactly where a utility is positioned in three dimensions, the designer can often make small adjustments in elevations or horizontal locations and avoid the need to relocate utilities. Additional information such as utility material, condition, size, soil contamination and paving thickness also assists the designer and utility owner in their decisions.