The U.S. construction industry is among the world’s largest, with annual expenditures of over $1.2 trillion. Construction projects are taking place all over the country, making the industry’s outlook a positive one. More and more, medium- to large-scale construction projects are implementing the practice of Subsurface Utility Engineering (SUE) at the design phase to reduce risk and save on long term costs. Subsurface Utility Engineering (SUE) is an engineering practice that makes it possible to more accurately establish the location of buried utilities within a project area. This provides a foundation for decision-making around construction design, allowing a designer to make important decisions related to utility coordination, utility accommodation and utility relocation at the outset.
And the gains are real. In 1996, the Federal Highway Administration commissioned Purdue University to study the cost savings realized from implementing SUE and found that for every $1.00 spent, $4.62 was saved.
What is the main objective of a Subsurface Utility Engineering program?
Simply put, Subsurface Utility Engineering cuts project risk and eliminates surprises at later stages of a project. It also saves money. However, not all SUE programs are created equal and there are key considerations involved to ensure that risk is effectively managed and a return on investment is realized.
Quality Level A (QL-A) provides the precise horizontal and vertical location of utilities along with type, size, condition, and material, which is obtained by exposing the utility, usually through vacuum excavation.
What exactly comprises a SUE program?
SUE is based on the CI/ASCE 38-02 Standard Guideline for the Collection and Depiction of Existing Subsurface Utility Data, which provides a framework for evaluating the integrity of data based on four Quality Levels:
• Quality Level D (QL-D): Information derived from existing records or oral recollections.
• Quality Level C (QL-C): Information obtained by surveying and plotting visible above-ground utility features and using professional judgment to correlate this information with the results of QL-D.
• Quality Level B (QL-B): The application of surface geophysical methods to determine the existence and horizontal position of subsurface utilities within a project’s limits. Non-destructive technologies including Ground Penetrating Radar (GPR) and Electromagnetic (EM) tools are leveraged at this stage to accurately detect conductive and non-conductive underground assets.
• Quality Level A (QL-A): Also known as daylighting, QL-A provides the precise horizontal and vertical location of utilities along with type, size, condition and material, obtained by exposing the utility, usually through vacuum excavation.
Does every project require all four Quality Levels?
Where a topographic survey exists that was recently completed by an engineer or surveyor, QL-C can typically be considered complete as surface utility data is captured during the topographic survey. The topographic survey should be correlated with information collected at the QL-D stage, to develop a starting point for the field investigation. Insights gleaned from combining these two datasets allow the investigation to be targeted and precise.
What is most important is that Quality Levels be carried out in their prescribed order – QL-D, QL-C, QL-B, QL-A. This is the most effective strategy for minimizing risk and avoiding rework. QL-D and QL-C should be applied to the entire project area including areas not expected to be affected by future construction, (e.g., temporary staging areas) whereas QL-B can be targeted to the impacted area. QL-A investigations are required when depth data or precise horizontal location must be obtained to achieve project goals. QL-A should also be considered when the results of a QL-B investigation appear to be conflicting with existing utility records in key project areas.
What factors can impact the SUE schedule? There are several factors that can affect the SUE schedule which should be considered in relation to a project’s overall timeline. Examples of these factors include:
• The client requests data acquisition activities that reside outside the scope of SUE which may result in project delays. For example, chamber investigations may require traffic control, night work, special permits and on-duty police scheduling and fees.
• Other activities occurring on the project site can impact the schedule, for example, topographical surveying, geotechnical or environmental assessments.
• The location of the SUE investigation. If the investigation occurs within a rail or congested vehicle corridor, traffic control and closures may be required. If however, the investigation is related to a boulevard or private construction land, there will be far fewer time constraints.
• The time required to review QL-B data, and schedule test pits. Determining the necessity, quantity and location of test pits usually occurs after reviewing the completed QL-B investigation and subsequent CAD utility drawing.
What deliverables should be provided?
SUE deliverable format s can vary greatly based on project specifications. Considerations for deliverables will include whether data is to be reflected on separate layers or a single layer, labelling conventions, CAD software format (MicroStation or AutoCAD), digital submissions vs. hard copy, color conventions, etc. The SUE report format may also vary based on whether the Project Manager desires photographs of test pits, test pit sketches, field sketches of utility locations, etc. When it comes to SUE deliverables, there’s a lot of room for customization to meet the unique needs of the project. Having said that, deliverables should always be overseen and stamped by a Professional Engineer.
Tips for carrying out a successful SUE project
Ensure that you and your team are familiar with the data collection activities that are standard for a SUE project and the data collection activities that reside outside of a standard SUE scope of work. For example, horizontal utility location data captured at Quality Level B and utility appurtenances captured at Quality Level C are standard – pipe invert and chamber measurements are not. A clear understanding of project scope will ensure that all required data is collected accurately and that no incorrect assumptions are made. Get familiar with the Scope of Work.
Every SUE project should commence with a project kick-off meeting that includes stakeholders such as the SUE Project Manager, Project Engineer, and Field Supervisor. If a topographic survey and base plan of the project area already exists, be sure to get a copy from the client. Topics to be discussed at the meeting should include any knowledge or documentation of existing or future utilities within the project area, proposed limits of the SUE investigation, expected deliverables, proposed SUE investigation timelines, project methodology, project-specific Quality Management and Health & Safety plans, and roles & responsibilities. Start each project with a kick-off meeting.
Develop a comprehensive memorandum that incorporates the CI/ ASCE 38-02 standard to ensure successful project execution. The memorandum should include a work plan, schedule, personnel hours and estimated cost. An onsite visit should also be carried out as it provides an opportunity to observe traffic conditions at different times, propose staging areas and locations, identify possible health and safety hazards, determine private and public property access locations, confirm control monument locations and assess parking restrictions. In advance of the field work, the project team will need to procure necessary permits; review existing utility documents, data and drawings; and secure buried asset records. Plan ahead.
Each SUE project should include a customized Health & Safety Plan that conforms to project-specific requirements. Traffic control is imperative and should include a documented plan that abides by municipal and state guidelines. Hazard assessments should be carried out to address potential hazards associated with traffic control including pedestrian traffic, weather patterns, visibility, etc. Required traffic control procedures and devices should be clearly documented along with procedures for safely setting up and removing devices and signage. Assess the health and safety certification requirements of the project site to ensure that all personnel have the necessary training. Make health and safety your top priority.
As SUE projects vary greatly in size and scope, unique and unexpected challenges can arise. Many variables can affect the ability to collect quality data such as broken tracer wires, soil conductivity, unexpected site obstructions, and conflicting record and site data. To keep projects on time and on budget, a quality project team may be required to innovate to overcome these unexpected challenges as well as increase stakeholder communications. Prepare for the unexpected.
Processes should be standardized, particularly during the data capture stage. While recording field notes, templates should be leveraged that guide the data collection process such as tracing, capturing GPS points, documenting field conditions and daily project status. The application of standard project management principles should be prioritized for disparate field data collections activities. Be consistent.
The CI/ASCE 38-02 Standard stipulates that “appropriate geophysical methods” be leveraged to carry out the Quality Level B aspect of a SUE program. As this is a generic statement, there is room for interpretation. Electromagnetic (EM) pipe and cable locating equipment is extremely effective at locating utilities comprised of or buried with electrically conductive material. When data collected at the QL-D and QL-C stages of a SUE program reveals a likeliness that non-conductive utilities reside on the project site, such as concrete or plastic pipes, buried trunk sewers, etc., other methods can be leveraged to supplement the SUE scope of work such as Ground Penetrating Radar (GPR), Time Domain Electromagnetics and Seismic Refraction. The decision to apply advanced geophysics needs to be weighed against the desired project outcome. Use the right technology.