Project Highlights:
- 500 Lane kilometers
- 5 Collection days
- No traffic disruption
Tetra Tech: 500 km Pavement Project
Founded in 1966, Tetra Tech is a leading global provider of consulting and engineering services, specializing in water, environment, infrastructure, resource management, energy, and international development. With over 28,000 employees across 550 offices worldwide, Tetra Tech leverages industry-leading technical expertise and sustainable approaches to deliver innovative solutions throughout the entire project lifecycle, from applied science and data analysis to engineering, design, and operations.
Project Overview
Tetra Tech used a Kontur Mk 4 AIR 3D Ground Penetrating Radar (GPR) system for non-destructive pavement assessment across approximately 500 lane kilometers of suburban, county, and rural and suburban roads in Alberta, Canada. This cutting-edge system, the first of its kind in Canada, employs step-frequency technology (100–3000 MHz) to achieve high-resolution imaging of thin pavement layers (down to 50 mm) and deep subsurface targets (several meters), facilitating detailed structural analysis without disrupting traffic.
Methodology
Kontur 3D GPR System:
The system features a 2.1-meter-wide air-coupled antenna with 25 receiver channels spaced 7.5 cm apart, floating 50 cm above the ground. This design allows data collection at traffic speeds (up to 100 kph, typically 30–55 kph) with minimal disruption. A sample interval of 10–15 cm ensures high-resolution data, geolocated using RTK GPS for precise alignment across swaths.
Data Collection:
Conducted over five days, one pass per road segment (northbound or eastbound), covering ~100 km daily. The system identifies targets both inline and crossline to the collection path, eliminating the need for transverse scans. Dense data sampling reduces the number of confirmatory pavement cores needed.
Processing and Analysis:
Performed using Kontur’s Examiner software, enabling rapid initial processing (even in the field), semi-automatic layer picking, and calibration with core samples. Outputs include heat maps, geolocated tables, radargrams, and KMZ files, with statistical analysis identifying anomalies like delamination or voids.
Deliverables
- Scope: Assessed ~500 lane kilometers to characterize pavement structure and detect anomalies or buried objects, supported by core samples for validation.
- Tabular Reports: Data averaged over 20-meter bins (~3300 samples/bin), reporting average depth/thickness and standard deviation for five interfaces: Asphalt Concrete Pavement (ACP), Medial, Base, Subbase, and Reinforcement. Includes georeferenced coordinates, street names, and chainage.
- Visual Reports: Feature a color bar showing ACP depth, cross-sections with picked layers (e.g., ACP, Medial, Base) cores, and inset maps for geolocation. Anomalous regions (e.g., variable thickness) are highlighted.
- Interfaces: An interface is the boundary between materials of the pavement.
- ACP: Depth to bottom, universally visible except on reinforced concrete sections.
- Medial: Weakly reflective layer within the granular base. Likely a change in grain size. Not always present.
- Base: Granular base bottom, harder to trace in older roads.
- Subbase: Weakly reflective, often intermittent.
- Reinforcment: Depth to rebar in bridges/concrete pads.
- Asphalt Layer Thickness: Examiner allows detailed analysis and semi-automatic picking of layer data. Layer thicknesses are calibrated using core data, with layer epsilon values either interpolated between data points or limited to regions of known similarity. Results can be visualized as heat maps of layer thicknesses or exported into tables tagged with geolocations. Statistical analysis of the layers allows fast identification of anomalous regions based on thickness or reflectivity, which may be related to delamination or void detection. Reports are delivered in geolocated KMZ files, tabular format with GPS locations, as radargrams, or as geolocated annotations.
Insights from Images
Radargrams:
Show depth (0–1.1 m) and distance scales with layer interfaces (e.g., ACP, Base) traced by colored lines (blue, orange), hyperbolic reflections indicating buried objects, and core locations (e.g., yellow bars at 1628 m chainage).
Aerial Views/Heat Maps:
Color-coded ACP base interface depths (0.2–0.6 m), with red/yellow areas indicating deeper layers or anomalies across multi-lane roads, geolocated with swath annotations.
Field Photos:
The Kontur system in action, towed by an SUV.
Key Findings:
The Kontur 3D-Radar system provides a robust, non-destructive method to map pavement structures and detect subsurface anomalies across extensive road networks. Outputs reveal variable layer thicknesses (e.g., ACP from 180–400 mm), with deeper or irregular regions flagged for potential issues like delamination or voids, calibrated by cores and visualized in detailed reports.
