Why Elevation Matters: The Hidden Variable in Compaction Testing
Most contractors treat compaction testing as a simple density check: hit the spec, move on to the next lift. But there’s a silent dimension in every compaction report that’s often ignored - elevation.
If you’ve ever looked through a Nuclear Density Gauge (NDG) compaction report, you’ve probably seen an “elevation” column next to each test. In theory, every NDG shot should include a true elevation reading, the height at which that test was taken, usually tied to a benchmark or mean sea level. In reality, those numbers are often rough estimates or copied from one test to the next.
NDG Field Compaction Testing
Does it measure up?
It might sound like a small detail, but elevation gives compaction testing an indispensable reference point. Without it, you can’t reliably verify lift thickness, connect density results to design, or defend your work when questions arise.
The Purpose and Importance of Elevation Measurements
The purpose of compaction testing is simple: to confirm that the soil or fill beneath your project can support what’s built on top. Elevation data ensures that each test result corresponds to the right lift and layer, the foundation of a defensible, quality-controlled compaction process.
Elevation ties each test to the correct lift
Suppose your project calls for 12-inch (1 foot) lifts. If you know the elevation at each test, you can confirm whether the correct amount of fill was placed. Without accurate elevation, you lose that vertical traceability.
Elevation provides defensibility
Adding elevation (and GPS location) to every test creates a 3D record, a verifiable map of what was compacted, where, and when. If questions ever arise, such as “Where was this test taken?”, you can pinpoint it precisely instead of relying on assumptions.
Recent research supports this direction. Studies on intelligent compaction and real-time GIS monitoring show that spatially referenced compaction data significantly improves quality assurance and traceability.
Lee et al. (2022) demonstrated that continuous elevation-referenced data creates a stronger, more reliable QA record.
Yao et al. (2023) highlighted that adding location and elevation transforms compaction reporting from 2D tables into actionable, 3D information.
3. Specs and Standards: Implicit but Often Ignored
Most RFPs and project specs imply the need for vertical control , even if they don’t say it outright. Typical specifications require that:
Each lift be leveled before compaction (implying vertical control).
Compaction properties be recorded for each constructed lift, which presumes knowing the lift’s elevation.
Tests represent the lift being compacted, meaning the vertical position must be clear.
(Source: Example Guidance for Compaction Specifications – ESOL, 2020.)
However, here’s the reality:
In most geotechnical scopes, there’s no budget or requirement to have a surveyor or survey-grade equipment on site at all times. The field crew’s job is to complete NDG tests efficiently, not to perform continuous surveying. As a result, elevation data often gets estimated, reused, or left blank altogether.
The Limitations and Realities in the Field
Even though elevation data is valuable, capturing it accurately in the field can be challenging.
Survey gear is rarely included
Few testing scopes include the cost of a surveyor or precision GPS setup. NDG technicians typically only have their gauge, not a total station or laser level. Without that equipment, true elevation data is difficult to obtain consistently.
Copy-pasted elevations
Many reports list the same elevation for multiple NDG tests, a telltale sign no real vertical measurement was taken. It saves time, but it also removes all spatial meaning.
Poor accuracy from handheld devices
Even when handheld GPS devices are used, vertical error can range by SEVERAL FEET depending on conditions. That’s enough to obscure the actual lift thickness being placed.
Workflow pressure
On busy sites, technicians often have dozens of tests to complete per day. Since it’s not part of their spec, budget, or performance criteria, elevation measurement falls off the checklist. In short: it’s rarely expected, so it’s rarely done.
Traditional Compaction Testing with NDG.
lacks the inherent ability to provide geospatial positioning data for test locations.
The Problems with “Estimated” Elevations
When elevations are estimated or copied across reports, the compaction record loses much of its value.
You lose context
Without accurate elevation, you can’t tell whether the test came from Lift 2 or Lift 3 — or whether it reflects material closer to subgrade or surface.
You can’t confirm lift progression
A site might require ten 12-inch lifts, but if all test elevations are identical, there’s no proof that 10 feet of fill was placed correctly. That undermines verification and QA.
You weaken defensibility
If every NDG test lists the same elevation, any reviewer - engineer, owner, or auditor - will question the integrity of the report. Once that trust is lost, so is the usefulness of the data.
You lose the core purpose
The point of compaction testing is to prove that the site was built to design specifications. Without reliable elevation data, you can’t prove that - and the report no longer fulfills its purpose.
How Compactica Solves the Problem — Elevation Built In
Compactica eliminates the need for guesswork by capturing elevation data automatically and pairing it with compaction performance in real time.
Automatic elevation capture
Compactica records elevation, GPS coordinates, and compaction data continuously, no manual input required. Every point becomes a verified 3D data record.
True lift-by-lift tracking
Because elevation is measured for every pass, you can visualize the site’s growth day-by-day or lift-by-lift. This provides immediate confirmation that the correct fill thickness is being achieved and compacted.
Visual and defensible reporting
Compactica’s reporting platform doesn’t just show compaction heatmaps, it provides:
Roller pass count heatmaps
Density / compaction performance heatmaps
Elevation heatmaps
Together, these visuals create a complete picture of what happened across the site: where compaction was strong, how terrain elevation changed, and how lifts progressed. That combination turns a static report into a fully traceable digital record.
*Maps based on sample data for illustrative purposes only
4. QA strength without extra burden
There’s no need for survey crews or separate elevation measurements. Compactica integrates this data capture into your existing compaction workflow, seamlessly and automatically.
Why This Matters
Compaction testing exists to ensure performance — that the material beneath your structures will not settle or shift.
But performance isn’t only about density. It’s also about verifying that the correct lifts were placed and compacted to design elevation.
Elevation connects those dots. It tells you:
What was built
Where it was built (vertically)
How well it meets specification
Compactica turns that from a manual process into an automated record — transforming compaction testing from guesswork into proof.
So, before your next project:
Ask whether your compaction reports show real elevation data for each NDG test.
Check if you can trace lift thickness or site progression through your current reports.
If either answer is ‘No’, reach out! We can help you build confidence into every roller pass and every compaction record, automatically.
References
Lee, S., Sharafat, A., Kim, I. S., & Seo, J. (2022). Development and Assessment of an Intelligent Compaction System for Compaction Quality Monitoring, Assurance, and Management. Applied Sciences, 12(14), 6855. https://www.mdpi.com/2076-3417/12/14/6855
Yao, S. (2023). Intelligent Compaction Methods and Quality Control. Smart Construction & Sustainable Cities, Vol 2. https://link.springer.com/article/10.1007/s44268-023-00004-4
Riad, M., Zhang, L., Liu, H., & Wang, J. (2022). Compaction Quality Assurance Specifications of Unbound Materials. Construction and Building Materials, Vol 348. https://mst.elsevierpure.com/ws/portalfiles/portal/40006773/Compaction_Quality_Assurance.pdf
FHWA. (2013). Intelligent Compaction: Executive Summary. U.S. Department of Transportation. https://www.fhwa.dot.gov/construction/pubs/hif13051.pdf