Utilising wireline geophysics for roading infrastructure investigations

September 8, 2026

The Situation

Identified as 3 separate sections of Roads of National Significance (RoNS), the Northland Corridor connects Warkworth to Whangārei over 100 km to the North of New Zealand.

The existing single carriageway faces numerous safety and weather resilience risks and a new, dual carriageway will unlock economic growth and productivity gains and provide more resilience during extreme weather events.

Technical Approach

As part of the ground investigation and feasibility studies for this roading project, an extensive drilling campaign was undertaken. As part of this drilling investigation, most of the boreholes were logged with wireline geophysical tools to better unlock geological and engineering insight along the alignment. The predominant tooling deployed included;

· Mechanical 3-Arm Calliper

· Acoustic Televiewer

· Optical Televiewer

· Natural Gamma

· Full Waveform Sonic

· P- & S-Suspension Logger

The data collected from each tool run was interpreted in conjunction with the core information collected from each borehole.

A number of boreholes were located deep in New Zealand bush and in difficult terrain, meaning that both drilling and wireline geophysical logging was only able to be undertaken by helicopter access only.

Figure 1- A typical heli-access drill location from the project site.

Outcomes

The high resolution imagery data from the Acoustic and optical televiewers enabled key defect information to be collected at each borehole, where highly fractured and seismically weak zones were identified and highlighted. These sometimes differed from the core information, further enabling the site geologists to differentiate between “in-situ” and “drilling induced” features, and providing an increased confidence level in their interpretations.

Figure 2- Typical Acoustic and Optical Imagery dataset from the project site.

Natural gamma logging was able to identify lithological changes through the geological profile, and highlight changes between Carbon-rich layers (such as clay’s and mudstone’s) and sand-rich layers (like gravels and sandstone’s). This was especially prevalent through changes between the Greywacke basement and the Northland Allochthon through the area.

Through the Brynderwyn hills, a proposed tunnel section required detailed engineering analysis to be undertaken, where P- and S-Wave velocities were able to be collected at depth using both the Full Waveform Sonic and P&S Suspension Logger. Both tools use an in-built source and at least two sensors, to provide a “true-interval” velocity calculation at each depth interval. Therefore, these methods aren’t subject to signal-noise losses at depth, and layer interval interpretations that are usually associated with downhole & surface seismic testing methods.

By collecting the compressional (P-) and shear (S-) wave velocities, alongside the lab calculated density data, the small strain elastic moduli profiles were able to be developed, including;

· Poisson’s Ratio

· Shear Modulus

· Bulk Modulus

· Young’s Modulus

Figure 3 - Example of Elastic Moduli data from the Full Wave Sonic tool and P&S Suspension Logger from the project site.

Summary

Utilising wireline geophysical techniques alongside a traditional geotechnical drilling investigate enabled an extra layer of information to be extracted alongside the typical geotechnical datasets.

Data was able to be compared alongside the alignment and fed directly into the geological model of the site, which was able to constrain the model even further.

The seismic information collected from the wireline geophysics was of higher resolution & accuracy than surface or downhole seismic methods, and didn’t have any of the associated investigation depth limitations (the only limitation was the depth of the borehole!).