Before subsurface utility engineering (SUE) was developed, engineers and designers had difficulty obtaining reliable underground utility information.
But over the years, SUE has evolved, enabling engineers and designers to get accurate information about underground infrastructure. The information has helped prevent project delays, utility relocation, redesigns, utility damage, and injuries thus reducing or eliminating all associated costs and risks.
If you're planning a construction project, this article is worth reading. We explore some of the methods and benefits of subsurface utility engineering for your project.
What Is Subsurface Utility Engineering?
Subsurface utility engineering is an engineering practice that combines surveying, civil engineering, and geophysics. The process helps manage risks associated with:
• Utility coordination
• Utility mapping at proper quality levels
• Utility condition assessment
• Utility relocation design and coordination
• Communication of utility information to relevant parties
• Utility design
• Utility relocation cost estimates
• Execution of utility accommodation policies
SUE, combined with site surveys, traditional record research, and new technologies like geophysics, gives you quality data for your project. In addition, SUE is entirely non-destructive and helps prevent utility damage stemming from your project.
Sanchez and Associates conducts subsurface utility engineering as part of asset management and information gathering typically at the design stage. This helps prevent utility conflicts in the later stages of your construction project, although subsurface utility engineering practices can also be applied during the construction phase for utility reverification and damage prevention.
What Are the Methods of Subsurface Utility Engineering?
SUE involves using various methods and technologies as defined by the American Society of Civil Engineers in a publication entitled “Standard Guideline for the Collection and Depiction of Existing Subsurface Utility Data” (ASCE CI 38-02). The Subsurface Utility Engineering standard establishes four levels of quality, each carrying a level of risk: The subsurface utility engineering quality levels are:
1. Subsurface Utility Engineering Quality Level D: Records Research / Data Collection
Quality Level D. The data gathered is solely derived from existing records and verbal information. As a result, the information from this level of Subsurface Utility Engineering is very limited in terms of accuracy and completeness. Since this is basically a gathering of existing knowledge of any underground utilities this serves best as a starting point for any project.
2. Subsurface Utility Engineering Quality Level C: Above-ground survey
Quality Level C. Survey of above ground utility features and then adds it to the existing Level D data. All the extra data usually raises more questions than it provides answers. This happens because it exposes discrepancies to Level D data by revealing utilities that have been omitted or incorrectly displayed. As a result, level C. by itself is most beneficial in the early stages of very large projects to determining the feasibility.
3. Subsurface Utility Engineering Quality Level B: Utility Designation
Quality Level B. also known as “designating”, determines the existence and horizontal position of utilities through the application of appropriate surface geophysical methods, i.e., EM locators, and ground penetrating radar (GPR). Level B. addresses common issues caused by inaccurate utility records, abandoned or unrecorded facilities, and lost references. This quality level of Subsurface Utility Engineering is most used as it provides valuable detailed information for designers and engineers.
4. Subsurface Utility Engineering Quality Level A: Test Hole / Potholing
Quality Level A. also known as “locating”, is the highest level of accuracy presently available. It provides verified information for the precise horizontal and vertical location of underground utilities through the nondestructive exposure of underground utilities utilizing vacuum excavation equipment., Typical data collected once exposed include utility type, size, depth, condition, material, and other characteristics of underground features. The method uses advanced technology and requires less labor to unearth underground utilities than traditional digging methods.
Benefits of Subsurface Utility Engineering on a Civil Engineer's Project in Illinois
Why go through all the hassle to obtain data on underground utilities before starting your project? Even if the process is not mandatory in your area, implementing it with your project can make all the difference. Here is how SUE can be beneficial to your project.
You should not rely on strictly on utility records since most have inconsistent data. An experienced SUE team will use various techniques grouped into four quality levels to help you get accurate data on underground utilities. In addition, the engineering process lets you figure out what kind of infrastructure is below the surface.
SUE methods provide the precise locations of underground utilities that could obstruct your project and cause delays. So even though the actual SUE process may delay your project by a few days or weeks, it will increase your project's efficiency in the long run.
Drilling into an underground utility pipe can cause a safety hazard affecting many people within the area. SUE helps detect underground utilities, minimizing potential hazardous situations during the project.
4. Minimizes Cost
You'll halt your project to deal with the damages if you run into an underground utility. Worse, you may be held liable for the repair costs to the damaged utility. Implementing SUE into your project also minimizes cost by reducing or eliminating utility redesigns, relocations, project delays, and injuries.
What are some tools used by Subsurface Utility Engineers?
1. Referencing Utility Records
Referencing utility records falls under the QL-D quality level and is a project's most basic utility information level. It involves getting data from verbal recollections or existing utility records, including plans from prior surveys, topographical surveys, and maps.
However, this method of subsurface utility engineering is limited in terms of accuracy and comprehensiveness.
Referencing utility records can be a good start for your project, but you should also incorporate other subsurface utility engineering methods. The data in utility records might be inconsistent, and not all utilities are listed in such documents.
2. Use of Electromagnetic Locators
Electromagnetic locators are a standard, noninvasive method of locating underground utilities and fall under quality level B standards. The EM locator uses an electromagnetic radio frequency transmitter and receiver to trace underground utilities. The transmitter emits a certain frequency which induces onto a targeted utility either directly or passively. The receiver detects the radio frequency emitted, allowing the locator to trace the pipes and cable.
3. Ground-Penetrating Radar (GPR)
Ground-penetrating radar falls under quality level B of subsurface utility engineering. It is a non-intrusive geophysical method that uses radar impulses to show objects underground.
Ground-penetrating radar can detect:
• Natural materials
Furthermore, you can use GPR on various surfaces, including ice, soil, rock, water, pavements, and structures.
Besides detecting underground objects, GPR exposes voids, cracks, and changes in material properties. The system also detects geological features and rock obstructions, excavated and back-filled areas, groundwater tables, bedrock, and changes in ground strata.
However, the functionality and readings of this underground imaging tool vary depending on site conditions.
GPR can reveal underground utilities buried up to 100 feet deep in low-conductivity surfaces like dry sand. High-conductivity surfaces like moist clays absorb or attenuate GPR signals, decreasing penetration depths by up to 3 feet. The GPR SUE tool uses specific software to translate signals into images, allowing you to see what's beneath the ground.
GPR is safe for public places and various project sites. It covers a large area and provides immediate and accurate underground utility data.
4. Vacuum Excavator
A vacuum excavator can help you unearth and verify underground utilities. The method uses advanced technology and requires less labor to unearth underground utilities than traditional digging methods.
Additionally, vacuum excavation services provide more accurate data on underground utilities. The method causes minimum damage to the underground structure and is safe. Some excavators are fitted with hydraulic power arms to increase maneuverability and speed with minimal handling.
Furthermore, a vacuum excavator can penetrate any surface, including rocky soil, clay, or frozen earth. Therefore, it is a cost-effective method of obtaining underground utility data.
Subsurface utility engineering is an essential aspect of any construction project, as it helps obtain data on underground utilities. You can choose between SUE methods like GPR, electromagnetic locators, and vacuum excavation services. The benefits of SUE include improved accuracy and efficiency, increased safety, and potentially reduced costs. If you're planning a construction project in the Midwest, contact us for subsurface utility services.