Ballast Investigation with Multi-Frequency GPR
Fouled ballast is the hidden root cause of track geometry degradation. KHEERAN’s IDS Saferail ground-penetrating radar system maps fouling, clean-ballast thickness and trapped water continuously along your corridor — without excavation, without track closure, reported by chainage within 24 hours.
Equipment: IDS Saferail System
Our hi-rail pickup truck carries three antenna lines surveying simultaneously in a single pass:
- Two 400 MHz ground-coupled antennas (left and right shoulders) — 1.5–2.0 m penetration depth, profiling full substructure including subballast and formation interface
- One 1 GHz air-coupled antenna (track centre) — high-resolution upper ballast fouling detection via void-scattering analysis
- GPS-tagged traces referenced to your chainage with forward-facing video synchronised at every point
The Science: How GPR Detects Fouling
Clean ballast scatters electromagnetic energy at 1 GHz in a characteristic pattern. As fouling fills the air voids with fine material, scattering amplitude drops measurably. Short-Time Fourier Transform (STFT) analysis of the radar signal at depth produces a colour map showing: clean ballast (high energy), gradational fouling, sharp fouling boundaries, and trapped water pockets (distinctive high-energy return flagged separately).
Fouling is quantified against the Selig Fouling Index (FI = P₄ + P₂₀₀): Clean < 10 · Moderately Fouled 10–20 · Seriously Fouled > 20. KHEERAN calibrates dielectric constants against samples from your route — granite typically 3.4–4.5, limestone higher — so every depth in the report is accurate for your actual ballast, not a generic database.
Survey Deliverables
- Fouling condition maps by chainage — separately for centre line and each shoulder
- Clean-ballast thickness profile, continuously along the route
- Trapped-water and ballast-pocket location flags
- GIS-compatible files importable into your maintenance management system
- Statistical summaries by segment with prioritised maintenance recommendations
- First-pass results within 24 hours of survey completion
Why GPR vs. Trial Pits?
A trial pit gives you one data point. Ten pits per kilometre still leaves 99% of the substructure uninvestigated. GPR delivers a continuous profile of your entire corridor at hi-rail vehicle speed. No possession beyond a standard hi-rail window. No excavation cost. No lab turnaround for every sample. A complete substructure picture — not a handful of snapshots.
Standards & Compliance
Survey methodology follows FRA research protocols, Transport Canada guidelines, and international NDT standards for railway substructure assessment. Fouling classification is calibrated to the Selig FI scale used across North America and Australia.