10/09/2026
SONIC DRILLING | COMPLEX COASTAL GEOLOGY | SOUTH ISLAND
Coastal ground conditions can present some of the more challenging drilling environments for geotechnical investigation â particularly where loose granular deposits, groundwater and oversized material combine within the same geological profile.
On the east coast of New Zealandâs South Island, our team is currently advancing boreholes through approximately 13 metres of highly variable pebble, sand and boulder deposits before encountering the underlying Papa bedrock.
This is exactly the type of ground where duo-head sonic drilling technology provides a significant technical advantage.
Sonic drilling uses high-frequency resonant energy transmitted through the drill string and sampling system. In heterogeneous formations, this assists advancement through materials ranging from loose sands and gravels through to cobbles and boulders, while allowing casing to be advanced concurrently to support the borehole.
From a geotechnical investigation perspective, the key objective isnât simply achieving depth â it is recovering a representative geological profile that gives the engineering team confidence in what is actually below the site.
In these coastal deposits, sonic drilling provides several important advantages:
⢠Continuous sampling through highly variable unconsolidated formations
⢠Improved recovery through loose sands, pebbles, gravels and mixed coarse deposits
⢠Simultaneous casing advancement to maintain borehole stability and isolate unstable formations
⢠Reduced risk of borehole collapse and cross-contamination between geological horizons
⢠Effective pe*******on through cobbles and boulder-rich horizons that can be problematic for conventional sampling methods
⢠Reduced water requirements, helping minimise disturbance and the generation of drilling fluids and spoil
⢠Larger-diameter sampling options where greater sample volume and geological definition are required
Importantly, reaching the bedrock interface doesnât mean reaching the limit of the drilling system.
Our duo-head sonic/rotary rigs allow the drilling methodology to transition from sonic sampling of the overlying coastal deposits to rotary diamond coring of the Papa bedrock, without mobilising a second drill rig.
That capability provides the geotechnical engineer with something particularly valuable â the ability to investigate the complete ground profile, including the critical transition from unconsolidated material into weathered and competent bedrock, using the most appropriate drilling method for each formation.
It is this combination of recovery, borehole control, drilling efficiency and methodological flexibility that makes sonic drilling such a powerful investigation tool in New Zealandâs complex geology.
The geology changes. The drilling system needs to be able to change with it.
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