Sonic is the new black
Environmental investigation on an abandoned mine site in the Northern Territory. Site was underlain with river gravels and sands making the Geoprobe 8140 sonic the most practical approach.
Sonic Drilling vs Direct Push: Why Legion Drilling Invested in Sonic Technology
Direct push sampling transformed environmental site investigations in Australia. When it was first introduced in the early 2000s, many consultants were sceptical about its ability to deliver high-quality, undisturbed samples. Over time it became the industry standard for contaminated land work - fast, clean, and effective in suitable ground conditions.
However, direct push technology has well-documented limitations. As investigation depths increase, rod friction often causes refusal in cemented sands, shale, dry clays, and competent rock. The small diameter of traditional dual-tube systems also means that installing monitoring wells usually requires a secondary reaming step with larger augers, adding time, cost, and potential for cross-contamination.
The Shift to Sonic Drilling
Recognising these constraints, Legion Drilling made a strategic decision to introduce sonic drilling technology to its fleet. The move was driven by a clear goal: to deliver continuous, high-integrity samples across a much wider range of geological conditions while improving efficiency, safety, and well installation outcomes for clients.
Sonic drilling uses high-frequency vibration to advance the drill string, dramatically reducing friction and allowing penetration through formations that routinely stop direct push rigs. The result is continuous core recovery with minimal data gaps even at depths exceeding 80 metres.
Two Distinct Sonic Systems, One Powerful Outcome
Legion Drilling initially deployed two different sonic drilling platforms to understand how each performed across Australia’s varied ground conditions.
One system uses a dual-tube approach similar to traditional direct push tooling, but with significantly more power, larger core diameters, and the ability to circulate fluid to the bit. This configuration excels in unconsolidated and contaminated formations where sample integrity and minimal cross-contamination are critical.
The second system follows a conventional coring methodology, with separate sample tube and casing strings. This design offers greater flexibility in mixed ground conditions and can be run with or without casing depending on formation stability. When fitted with a high-speed rotary head and automatic SPT hammer, the same rig can seamlessly switch between sonic sampling, diamond coring, and standard geotechnical testing, delivering true multi-purpose capability on a single mobilisation.
Key Advantages of Sonic Drilling
Legion Drilling’s experience with sonic technology has consistently demonstrated clear benefits for contaminated land and geotechnical projects:
Greater Depth Capacity Reliable continuous sampling to 80 m+ with no data gaps, allowing accurate targeting of zones of interest and confident well screen placement.
Larger, Higher-Quality Samples Core diameters from 75 mm to 150 mm provide excellent sample volume for laboratory testing.
Simplified Well Installation Larger diameter boreholes create sufficient annular space for high-quality groundwater well and instrumentation installation without secondary reaming.
Exceptional Formation Flexibility Effective across sands, silts, clays, landfill, fresh rock, and fractured rock with excellent recovery rates.
Reduced Waste Volumes The close tolerance between drill string and sample diameter significantly cuts spoil generation compared with hollow auger methods.
Improved Safety Hydraulic rod handling, breakout clamps, and the absence of high-speed auger flights reduce manual handling risks.
Operational Considerations
Sonic rigs are larger machines (typically over 10 tonnes with mast heights around 7 m). While track-mounted and relatively light on their feet, access and site storage requirements should be assessed early in project planning. Fluid circulation may be used in deeper or more competent formations to aid cuttings removal and maintain borehole stability.
Why Legion Drilling Continues to Lead with Sonic
More than a decade after introducing sonic drilling, the technology remains a cornerstone of Legion Drilling’s service offering. We continue to invest in the latest sonic rigs, tooling innovations, and operator training because sonic consistently delivers superior results where direct push reaches its limits.
For projects requiring reliable data at depth, clean well installations, or investigation in challenging geology, sonic drilling is no longer an alternative , it is often the smarter, more efficient choice.
Need sonic drilling or high-resolution site characterisation for your next project?
Contact Legion Drilling to discuss how our sonic capabilities can improve data quality and reduce project risk on your site.
Geoprobe 8140LS Sonic in action on a remote site in the eastern NT Australia.