How Ground Penetrating Radar Saves Money, Time, and Reduces Risks during Construction

How Ground Penetrating Radar Saves Money, Time, and Reduces Risks during Construction

A challenge present in every project is managing risk and reducing or eliminating unknown elements prior to construction. Significant risk can be present when subsurface conditions are not documented or investigated prior to the start of work. Dealing with these unearthed items can be very costly to demolish, repair or reroute and can create a need for urgent redesign amidst the chaos of construction. Early use of ground penetrating radar (GPR) on a project can greatly reduce these risks.

Common Construction Issues

Unknown buried obstructions and utilities, resulting in costly construction delays, are commonly encountered for several reasons. Many older facilities lack complete and accurate records to pinpoint the locations of buried infrastructure. Additionally, abandoned items underground such as foundations, storage tanks, vaults and utilities were typically left in place due to the inherit cost of full removal. Any new project proposed in these locations will have to absorb costs and schedule impacts to address these items. Depending on what is found, the issue could be quite expensive to correct, especially if it ultimately involves environmental remediation.

Notification to the state sponsored utility locating service (e.g., 811 or Miss Dig) is required prior to commencing with any excavation. However, this service only applies to public utilities. Plant utilities will not be covered by this service and are the responsibility of the owner to determine impact and perform any necessary modifications. This is where a private service utility locating provider can fill in the gaps and reduce risks for new projects.

Proposed underground utilities also may require a connection to an existing buried utility in which the actual position is unknown. Identifying an accurate tie-point for these utilities can be critical, especially when proper slope must be maintained, such as for a gravity-drained sewer.

Voids and Sinkholes

Voids and sinkholes may exist below the surface with no indication above ground. These are typically formed when a buried utility or structure below is washed out or when improper backfill and subbase below grade settles, leaving a vacant pocket in the soil. Sometimes when this occurs in a paved area, the pavement above can bridge the void leaving a cavity below that is not visible above grade. These voids can be detrimental to large equipment or heavy traffic as well as for crane outriggers that may punch through the surface when an unknown void is below, thus creating a serious safety concern to personnel as well as a definite impact to plant operations.

Embedded Items in Concrete

Determining the condition of existing concrete slabs and walls is important when evaluating new equipment loads or deciding if a portion of the concrete can be cut out to route new utilities or structures. Common items embedded within concrete that can cause complications if encountered include:

  • Electric and communication wires/conduits
  • Drains and process utilities
  • Reinforcing bars
  • Building post-tension hairpins

The Solution – GPR and Utility Locating

If information on subsurface conditions can be obtained early in a project, the engineer can account for these items in the design and avoid costly impacts during construction. Projects where this information will be crucial include any projects involving:

  • New equipment or building foundations
  • New or rework to buried utilities
  • Site work and grading
  • Large crane setups
  • Coring through walls and slabs

Matrix Technologies uses cutting-edge technology, ground penetrating radar (GPR) and radio utility locators to provide insight into subsurface conditions not visible above ground without requiring expensive excavations.

Ground Penetrating Radar (GPR)

Ground penetrating radar works by sending radar pulses from a transmitter into a material and the receiver records the time and strength of any reflected signal. Information is gathered as the reflected radar signal changes when it passes through a material with different properties, creating a parabola to identify an anomaly or obstruction.

Varying antenna frequencies transmit differently through each medium and are used for varying subsurface investigation purposes. Typically, the lower the frequency, the deeper the penetration. Therefore, Matrix Technologies, Inc. uses both a 400 MHz antenna and a 1600 MHz antenna in order to gain an accurate picture underground at various depths. The 400 MHz antenna can scan depths between 2 and 15 feet, depending on site and soil conditions. The 400MHz antenna is used for locating utilities, underground voids or other abnormalities. This antenna is operated using a three-wheeled cart allowing for large areas to be scanned in a short period of time.

The 1600 MHz antenna provides a detailed scan up to 18 inches deep. The 1600 MHz antenna is used for determining concrete thickness, rebar location and voids under pavement. This antenna can be operated using the large cart or a smaller handheld unit, allowing it to be used in smaller spaces or along vertical walls and ceilings.

This equipment is non-intrusive and does not emit radiation so plant operations occurring in proximity to the scanner are uninterrupted.

Although GPR is very useful for providing subsurface imaging without the need for excavation, it does have limitations that need to be considered. Site conditions such as soil conductivity and material properties can play a factor in the data the GPR is able to collect. Soil conductivity is the measure of how well electromagnetic signals pass through a medium. The lower conductivity, the further the signal can travel.

Low Conductivity (Deep GPR Penetration):

  • Dry soil
  • Sand
  • Concrete

High Conductivity (Shallow GPR Penetration):

  • Saturated soil
  • Clay

The material composition and diameter of the target also factor into the GPR’s ability to “see” it. Metallic items reflect the radar signal much better than plastic objects. Also, a good rule of thumb for target size is that GPR can typically see an object 1 inch in diameter per foot of depth scanning (e.g., 4-inch diameter pipe, buried 4 feet).

Radio Detection

Matrix Technologies also uses the RD 8100 radio detection utility locator. Radio detection  works by sending radar pulses through the ground to detect electric current and metallic pipe. It uses five different antenna frequencies to optimize the level of precision for each utility/material to be located. To further enhance this equipment, Matrix Technologies uses an iLOC induction tracer clamp, which connects around pipe risers where they come above grade and electromagnetically traces underground utilities for a distance of up to 1,400 feet.


Ultimately, GPR and utility locating is a safe, valuable and non-invasive technique to gather subsurface information. No matter the scale of the project, having this service completed early is a cost-effective way to help eliminate expensive redesign/rework and adverse schedule implications due to inaccurate information in the design phase. Additionally, knowing what is hidden below grade greatly reduces safety concerns associated with excavation during construction and potential impacts to plant operations.

The Matrix Difference

Matrix Technologies is different from many other utility locating companies. In addition to using the latest technology, each of our GPR technicians are engineers with experience in site layout, underground utility and structural design. This knowledge helps technicians have a full picture and better understanding of site conditions, as well as be able to provide engineering solutions when items are unearthed in the field.

Matrix Technologies provides onsite field markings as well as a formal report documenting the results of the subsurface GPR scan. Additionally, Matrix Technologies can provide topographic surveying and 3D laser scanning to accurately document the field information. Matrix Technologies also can create and manage CAD and 3D models for site layouts and utility plans.

While subsurface investigation using GPR and utility locators is a critical step in the design process, it is typically supplemented with other field services and engineering. Matrix Technologies provides a wide range of field services and multi-discipline consulting engineering, thus creating a one-stop shop that eliminates the time, effort and potential coordination concerns associated with hiring separate contractors or engineers to perform this work.

Matrix Technologies is one of the largest independent process design services, industrial automation engineering, and manufacturing operations management companies in North America. To learn more about our manufacturing operations management capabilities and manufacturing process control solutions, including field services including GPR and utility locating or other engineering capabilities, contact Joe Leech, PE, Engineer 4 in the Mechanical & Facilities Design Department.

© Matrix Technologies, Inc.

Enterprise Asset Management

Enterprise Asset Management

John Lee, Strategic Manager of Manufacturing Intelligence at Matrix Technologies discusses how to increase productivity, up-time and reduce operational costs using Enterprise Asset Management (EAM) in a manufacturing facility. EAM goes beyond computerized maintenance and management systems.

Matrix Technologies is one of the largest independent process design, industrial automation engineering, and manufacturing operations management companies in North America. To learn more about our manufacturing operations management capabilities and manufacturing process control solutions, contact John Lee, Senior Manager of Manufacturing Intelligence.


Pipe Stress 102 – How Stress Analysis can Prevent Issues in Your Facility

Pipe Stress 102 – How Stress Analysis can Prevent Issues in Your Facility

This is the second article in a series of articles about thermal stress, pipe stress, and the art of pipe stress analysis. The first article provided a look at thermal expansion and contraction and an idea of the magnitude of thermal growth you could expect to see from a hot pipe. This second article will take a closer look at the importance of proper stress analysis and good engineering practice to offset the risks that thermal expansion poses to piping and equipment.

Piping systems are complex, running the length and width of a plant. Piping runs to every major piece of equipment and every tank, often over long distances. The pipes that carry hot liquid, steam, or other hot gasses will experience thermal expansion. If you recall from our previous article, this ultimately serves to increase the pipe’s length. Pipes that carry cryogenic or cold substances will experience thermal contraction and the pipe’s length will decrease. Both of these instances can wreak havoc in the plant unless properly designed and planned for.

What is Pipe Stress Analysis

So what exactly is Pipe Stress Analysis? Pipe Stress Analysis, in simple terms, is the calculation of the forces and movements on a piping system. Movements typically result from thermal expansion or contraction. Forces may result from this same expansion or from external forces such as deadweight, movement of equipment, and wind or seismic loading. In this article, we will focus on the forces generated from thermal expansion and how a stress engineer might deal with them.

Where thermal growth meets a fixed object, like a piece of equipment, you get a force. Forces acting over an area result in a stress. Stress Analysis calculates the forces, and the resulting stresses, and designs flexibility into the piping system so that these forces and stresses do not become excessive. When I use the term flexibility, I don’t mean just the routing but also the specific types of supports or restraints that might be required to control the movement of expanding pipe as well.

I believe the best way to explain something is with an example. Let’s consider the two runs of pipe below. The first is a straight run between two points that are anchored. The second has a perpendicular portion in the middle, with two elbows. If both of these pipes were heated to 300°F which one would generate the most axial force? You might intuitively guess the straight pipe has the higher anchor load, but can you guess the difference between the two?

Figure 1: Two Pipe Routings, Both Anchored at Either End – Shown Cold

The straight pipe, in carbon steel, travels 20 feet from left to right and generates 260,000 lb of force against the anchors at 300°F. There are no additional forces acting on the pipe, so the forces on the anchors are entirely from thermal growth. If you recall from the previous article, carbon steel pipe at 300°F will grow 1.9 inches per every 100 ft, so this 20-foot section will grow 0.38 inches (just about 3/8 of an inch). Remember how I mentioned before that it wasn’t so much the thermal growth in a pipe that was the problem, but what the pipe is pushing against. This pipe, bound on both sides by an anchor generates 260,000 lb of force. Now that anchor out in the world might be a steel from a platform, or a piece of equipment. In either case the loading is likely to be too high.

Figure 2: Same Two Pipe Routings from Figure 1 – Shown Hot

So how much force does the second pipe route generate? You can tell from this second picture, where both pipes are in their hot position. Note that the thermal growth is shown exaggerated a bit so it’s easier to see. It’s evident that the second pipe route has more flexibility. There are two elbows and a change of direction that allows the growth from thermal expansion to bend the pipe and flex the elbows as opposed to just pushing directly against the anchors on either end.

So if I told you both pipes were configured the same, same temperature, same length from left to right, same anchors on both ends, same material, could you guess the axial load on the bottom pipe? Half of the load generated by the top pipe? One quarter? How about less than 1%? Where the straight run of pipe generates nearly 260,000 lb of force on its anchors, the bottom run of pipe generates only 2,020 lb of axial force on its anchors. Yes, there is some bending moment from the pipe flexing, but in comparison to the loading from the straight run of pipe the moment at the anchor is still less than 1.5%.

Engineering Methods for Handling Thermal Expansion

The example above helps explain why hot piping isn’t usually routed in long straight runs. However, sometimes long straight runs of pipe can’t be avoided in the distances between major pieces of equipment in a facility. This is where stress engineers can employ special geometry, like an expansion loop, to absorb the thermal growth of the pipes. You will typically find these loops located in pipe racks, where typical expansion loop may look something like the piping shown in figure 3 below.

Figure 3: Straight Pipe Route with Expansion Loop – Shown Cold

In figure 4, the same pipe route with expansion loop is shown when it’s at 300°F. Note how the thermal growth occurs at the inner elbows of the loop. In this configuration, the axial load on the anchors is about 2,040 lb, similar to the bent configuration in figures 1 and 2. It is interesting to point out that while the axial movement at the inside elbows is 0.35 inches on each side, the perpendicular movement at the same point is nearly 1 inch. The piping is more flexible in the perpendicular direction so when thermal growth forces the inner elbows together the piping naturally bows.

Figure 4: Straight Pipe Route with Expansion Loop – Shown Hot

If this perpendicular movement were too high, perhaps there are other pipes nearby that we don’t want to grow into, or perhaps this bowing creates an excessive moment at the anchors on either end of the line, then there are special supports designed with this in mind that help restrain the piping laterally while allowing the pipe to grow axially. These supports are called Guides. See how, in figure 5, the thermal growth is restrained to the axial direction of the pipe when using Guides on either side of the expansion loop.

Figure 5: Straight Pipe Route with Expansion Loop and Guides – Shown Hot

In this configuration, the axial movement at each inner elbow is about 0.35 in, similar to the unguided configuration in Figure 4. However, the perpendicular movement of the pipe had dropped to just 0.24 inch. The axial force at each anchor is a little higher at 2,500 lb, but still less than 1% of the forces generated by the straight pipe in the first figure.

Remember Pipe Stress Analysis isn’t just about determining what forces or stresses are generated, but also about calculating how much flexibility is in a run of pipe. The stress engineer has to determine whether a particular run of pipe is flexible enough and if loads on equipment and supporting steel are too high. If so, the engineer then has to determine what changes to the routing and supports might be necessary to reduce the loads. In later articles, we will go into more detail about the different types of supports, their uses, and how the design of piping for thermal expansion and corresponding forces on equipment are governed by various Codes. In the next article however, we will discuss what to look for in your own facility. Are there telltale signs of uncontrolled thermal expansion at your site?

Matrix Technologies is one of the largest independent process design, industrial automation engineering, and manufacturing operations management companies in North America. To learn more about thermal expansion and pipe stress analysis, contact Chris Mach, Senior Consultant or Brandon Grodi, Mechanical Department Manager.

© Matrix Technologies, Inc.

Bottling Line Overall Equipment Effectiveness (OEE) Simulation

Bottling Line Overall Equipment Effectiveness (OEE) Simulation

Drew Robertson, PE walks through a spirits bottling line simulation. By using process analysis we are able to quantify OEE increases based on conveyor speeds and equipment speeds. This can help calculate a Return on Investment (ROI) assessment.