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Unexpected Setbacks During Construction - Using GPR to Mitigate Risk

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 inherent 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.

Proposed underground utilities may also 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 may also 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 serious safety concerns to personnel as well as a definite impact to plant operations.

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 the concrete that can cause complications if encountered include:

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

If the 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

Sustainable technology with lifecycle influence

Clean, safe, efficient, and sustainable, GPR investigations provide an opportunity to optimise cost, work schedule and environmental impact as part of built asset maintenance and upgrade schemes.

The highly mobile, remote sensing nature of the technique can substantially mitigate health and safety risks associated with the investigation of congested, trafficked or difficult-to-access locations, reducing the need to place survey personnel in high-risk environments.

Multiple applications and benefits

From rail and road infrastructure to critical energy, water distribution networks and coastal and flood defence structures, and residential, commercial and industrial sites, GPR can reduce uncertainty and add project value by:

  • Providing continuous mapping to inform shallow sub-surface hazards, structural conditions and defects
  • Corroborating and extracting a better understanding of other pre and post-construction data
  • Targeting, rationalising and optimising intrusive physical sampling strategies (such as coring)
  • Helping define a robust ground or structure model that can be used as the basis for efficient, ongoing management of asset inspection, monitoring, maintenance, and improvement through to end of service life
  • Providing key structural information to inform design decisions and remediation to extend the working life of critical infrastructure.

Vital data collection for project and asset management

GPR also has the advantage of superior data processing capabilities in most cases, meaning it delivers a clearer and more accurate picture of unmarked underground utilities, structures, and reinforcing members faster.

It takes less time to do the scan and to interpret the results, meaning less interference and downtime. More importantly, you can use GPR equipment without having to shut down significant areas of the site during the test in order to get a clear picture. This gives you the information you need to help you decide how, when, and where the ideal place is to make cuts, core samples, and perform other operations without risk of damage to subsurface utilities.

Intrusive work such as coring provides only a point reading or ‘stick’ data, in contrast to GPR which fills the detail in between, picking up unseen problems and anomalies. A GPR survey allows the fast screening of large areas to identify areas of concern in order to better target and optimise intrusive work and drive sufficiency in investigation efforts.

GPR data delivers insights as a component of a number of solutions within the Ground Risk Management Framework (below), but with a focus on investigating the performance of operational assets as part of a structural health monitoring solution.

Synergy can supply your business or project with all the necessary tools for successful project management plus ongoing monitoring solutions to future proof your assets. Click here for more information on our GPR solutions.

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Conclusion

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.

Whether constructing on undeveloped land or on an existing developed site, there is a risk of encountering unexpected objects in the construction process. With today’s technology in Ground Penetrating Radar (GPR), this risk can generally be mitigated saving time and costs.

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