Striking an underground service is one of the most avoidable yet persistent risks in construction.
Despite improved regulations, better mapping technology, and increased awareness, service strikes continue to cause injuries, programme delays, financial losses, and reputational damage across the industry.
Below are some of the most common mistakes made when locating underground services — and how they can be avoided.
Relying Solely on Utility Records
Utility drawings and statutory records are always a starting point. They provide valuable context and indicate known services within and around a site. However, treating them as definitive is one of the most common and dangerous mistakes on site.
Records are frequently outdated, incomplete, or inaccurate. Services may have been diverted without updated documentation. Redundant infrastructure may not be recorded at all. Depths are often estimated, and horizontal positions can vary significantly from what is shown on plans.
On brownfield or urban sites with decades of layered development, discrepancies are particularly common. Assuming drawings reflect reality without verification can lead to excavation decisions based on flawed information.
Best practice is to use records as guidance, not confirmation — and to validate them through physical detection methods before work begins.
Over-Reliance on a Single Detection Method
Another frequent mistake is depending on one detection technology alone. No single method can identify every type of underground service with complete accuracy.
For example, electromagnetic locators are effective for detecting metallic services or those carrying a current. However, they struggle with non-metallic utilities such as plastic water pipes, fibre optic ducts, and some drainage systems.
Ground Penetrating Radar (GPR), on the other hand, can detect both metallic and non-metallic objects by identifying changes in subsurface material. Yet even GPR has limitations depending on ground conditions and depth.
The most reliable approach combines multiple detection methods. Using complementary technologies reduces blind spots and increases confidence in the findings.
Failing to Investigate Early Enough
Underground investigations are sometimes left until just before excavation, often due to programme pressure. At that stage, findings can create disruption rather than clarity.
If unknown services or obstructions are discovered late, redesigns may be required, plant may need to be rescheduled, and teams can face costly delays. Early-stage investigations allow risks to be managed proactively rather than reactively.
Carrying out service detection during feasibility or pre-construction stages enables designers to work with verified constraints, improves cost forecasting, and supports more realistic programming. Early insight almost always reduces downstream disruption.
Assuming “Clear” Areas Are Risk-Free
It is common to focus attention on congested zones shown on utility drawings while assuming open areas are clear. In reality, many service strikes occur in locations believed to be low risk.
Redundant services, private networks, and undocumented diversions often exist outside the main utility corridors. Historic site alterations can leave behind isolated services that are no longer connected but still physically present.
Even where detection surveys indicate no services, cautious excavation practices should still be followed. Verification through trial holes or vacuum excavation may be necessary in higher-risk environments.
Misinterpreting Survey Data
Collecting data is only part of the process; interpretation is equally critical. Misreading survey outputs or failing to understand the limitations of detection methods can result in incorrect conclusions.
For example, GPR data requires skilled analysis to distinguish between utilities, natural ground features, reinforcement, or other buried structures. Inexperienced interpretation can lead to false positives or missed anomalies.
Clear reporting, properly marked drawings, and collaboration between surveyors and project teams are essential. When findings are not fully understood, risks can re-emerge despite having carried out a survey.
Engaging experienced specialists, such as us at Intersect Surveys, ensures that survey results translate into practical, reliable site decisions.
Ignoring Depth and Vertical Separation
Knowing that a service exists is only part of the picture. Understanding depth and vertical positioning is just as important, particularly when excavation levels, piling, or ground reduction are involved.
Services may cross at different depths, creating layered risk zones. Without accurate depth data, teams may assume adequate clearance when in reality a deeper excavation could expose or damage a utility.
Depth estimation varies depending on detection method and ground conditions, so findings should always be reviewed in context. Combining detection data with careful excavation planning significantly reduces the likelihood of unexpected contact.
Moving from Assumption to Assurance
Underground services will always present some degree of uncertainty, particularly on complex or historic sites. However, many of the most serious incidents and delays stem not from unavoidable risk, but from preventable mistakes in how that risk is assessed.
For both industry experts and those new to site investigations, the principle remains the same: assumptions underground are expensive. Verification is far more cost-effective.
Understanding what lies beneath your site is not just about avoiding damage — it is about enabling safer construction, clearer commercial decisions, and stronger project outcomes from the very beginning.
Get in touch with Intersect Surveys today to book your survey!
