Utility Locates 2 Flashcards
What are 4 steps you can take when troubleshooting a challenging utility locate?
- Change your Grounds. - move the ground stake to opposite side of utility.
- Change your Frequency - means venturing from the frequencies you might be most comfortable with and trying others that are available on your locator. Even if it’s counter intuitive to what you learned early in your career, and even if that one frequency “always works for you,”
- Change your power method - Direct Connect, Inductive, Coil clamp
- Change your angle or move - Imagine you’re locating at a person’s house, and you’re having trouble finding the service. Locate the neighbor’s service to the main, and locate the main back into the customer’s service that you’re trying to find. A lot of times, using this method means you’ll get current to flow better and you’ll have more success.
- consider grounding to a stop sign or something
How far away from utility markings should I tell the drill team to move the boreholes?
We should offset boring by 6 feet away from any utility markings. We don’t know how big a utility is. It could be a duct bank that’s 6 feet wide.
When relocating a boring marker, how far away should we be away from ground wiring/drill rig obstacles (overhead too!)
Minimum 15 feet away.
Avoid high volume parking spaces.
Maximum we can offset borehole without calling PM/consulting client?
25 feet
Aside from differences in dielectric, what other factors can contribute to a stronger gpr signal reflection %?
Denser, more compact soil/materials yield a stronger signal reflection.
What are some soil properties that cause GPR signal to disperse more?
Clay-rich & ion rich soils (More:)
Electrical Conductivity: Soil conductivity, often influenced by factors such as moisture content, mineral composition, and salinity, can affect the propagation of electromagnetic waves emitted by GPR antennas. High soil conductivity leads to greater signal attenuation and dispersion, reducing signal penetration depth and resolution.
Dielectric Constant: The dielectric constant of soil, which represents its ability to store and transmit electrical energy, affects the velocity of electromagnetic waves in the subsurface. Soils with higher dielectric constants tend to exhibit slower wave velocities and greater signal dispersion, resulting in reduced resolution and imaging quality in GPR surveys.
Moisture Content: Soil moisture content plays a significant role in GPR signal dispersion, with wetter soils generally exhibiting greater signal attenuation and dispersion compared to dry soils. Moisture-filled pore spaces increase soil conductivity and alter the dielectric properties of the soil, leading to increased signal scattering and reduced penetration depth.
Soil Texture and Porosity: Soil texture, including particle size distribution and packing density, influences the porosity and hydraulic conductivity of soil, affecting its ability to retain moisture and transmit electromagnetic waves. Coarse-textured soils with high porosity and low water retention capacity tend to exhibit lower signal dispersion compared to fine-textured soils with greater moisture retention.
Soil Compaction and Density: Soil compaction and density influence the propagation of GPR signals by altering the mechanical properties and moisture content of the soil. Compacted soils with higher density and lower porosity tend to exhibit lower signal dispersion and greater signal penetration depth compared to loosely packed soils with higher porosity.
Mineral Composition: The mineral composition of soil, including the presence of clay minerals, organic matter, and mineral aggregates, affects its electromagnetic properties and signal dispersion characteristics. Soils with high clay content, organic content, or mineralogical variability may exhibit greater signal dispersion due to variations in electrical conductivity and dielectric properties.
Groundwater Level: The depth and fluctuation of the groundwater table can influence GPR signal dispersion by altering soil moisture conditions and conductivity profiles in the subsurface. High groundwater levels and water-saturated soils tend to exhibit greater signal dispersion and attenuation compared to dry or partially saturated soils.
What are 5 considerations for site walkdowns?
When performing a site walkdown to locate buried utilities before conducting a scan with ground-penetrating radar (GPR) or other geophysical methods, here are some tips to consider:
Review As-Built Drawings: Obtain and review as-built drawings, utility maps, and construction records for the site to identify the location and depth of known utilities. As-built drawings provide valuable information about the layout and configuration of buried utilities installed during construction.
Mark Utility Flags and Markers: Look for utility flags, markers, or paint markings on the ground surface that indicate the presence of buried utilities. Utility companies and contractors often use color-coded flags or paint to identify the location and type of buried utilities.
Identify Utility Access Points: Locate utility access points, such as manholes, valve boxes, and utility meters, that provide entry points to underground utility systems. Access points can help trace the path and direction of buried utilities and verify their location during scanning.
Observe Surface Indicators: Look for surface indicators of buried utilities, such as utility poles, above-ground equipment, utility covers, and utility service connections to buildings. Surface indicators can provide clues about the presence and location of buried utilities beneath the ground surface.
Use Ground Penetrating Radar (GPR): Consider using GPR or other geophysical methods to supplement your site walkdown and verify the location of buried utilities. GPR can provide real-time subsurface imaging and detection of buried objects, helping to confirm the presence and depth of utilities identified during the walkdown.
By following these tips and conducting a thorough site walkdown before performing utility scanning with GPR or other methods, you can improve the accuracy and effectiveness of your utility locating efforts and minimize the risk of damaging underground infrastructure during construction activities.
Tips & Tricks when reviewing As-build Drawings?
Tip: Pay attention to the accuracy and completeness of the as-built drawings and utility maps. Inaccuracies or missing information can lead to discrepancies between the documented utility locations and the actual field conditions.
Trick: Cross-reference as-built drawings with historical aerial imagery, satellite photos, and street view images to identify changes in utility infrastructure over time. This can help detect undocumented utility installations, abandoned lines, or recent construction activity that may not be reflected in the drawings.
Tips and tricks when Identifying Utility Access Points
Tip: Use utility access points as reference points for mapping and tracing buried utilities. Manholes, valve boxes, and utility meters often mark key locations where utility lines intersect or change direction.
Trick: Follow utility corridors and trace the path of utility lines from access points outward using a systematic grid or line tracing method. This can help create a comprehensive utility map and identify potential conflicts or deviations from the expected utility routes.
Observing Surace Indicators Tips and tricks
Tip: Look for subtle surface features and anomalies that may indicate the presence of buried utilities, such as depressions, patches of disturbed soil, or vegetation patterns. These surface indicators can provide valuable clues about the location and alignment of underground utilities.
Trick: Use a combination of visual observation and geophysical surveying techniques, such as GPR and electromagnetic (EM) conductivity surveys, to confirm the presence and location of buried utilities identified by surface indicators. Ground-truthing surface anomalies with geophysical data can help validate interpretations and improve the accuracy of utility mapping.
Tips and tricks - Interpreting Surface Infrastructure
Tip: Consider the layout and configuration of surface infrastructure, such as utility poles, junction boxes, and service connections, when interpreting buried utility locations. Underground utilities often follow logical pathways and alignments based on surface infrastructure and property boundaries.
Trick: Verify the continuity and connectivity of surface infrastructure with subsurface utilities using GPR surveys and utility tracing methods. Identify potential points of intersection, branching, or convergence between surface features and buried utilities to refine utility mapping and avoid misinterpretations.
Strategy for complex congested areas?
Go to an uncongested area and locate back to the source (congested area) and, if possible, the next visible indicator.
What is something you can do to improve the circuit / connection in a sandy environment?
in areas with dry, sandy soil where it can be difficult to create a proper circuit, pouring water around the ground stake can improve the circuit. Sometimes, using a larger grounding stake than the one provided with most transmitters improves the circuit.
General common utility depths?
0-10ft
How deep should I drive the grounding rod?
About 8 feet, 6-10ft, or at minimum the depth of the utility(?).
Depth of Utilities: Consider the depth of the utilities being located when selecting the ground reference location. Position the ground reference at a depth comparable to the utilities to ensure accurate depth measurements and minimize depth estimation errors.
