Testing with the PANDA variable energy DCP in Hawke's Bay, NZ
Geovert has added the PANDA® Variable Energy Dynamic Cone Penetrometer to its geotechnical investigation capability. On Mohaka Coach Road in Hawke’s Bay, it allowed WSP to characterise a landslide face that a drill rig or CPT vehicle could not have reached in a useful way.
Overview
WSP engaged Geovert to investigate a landslide face adjacent to the road corridor. Establishing whether bedrock was present was not the goal. WSP needed to know how deep the rock and soil interface sat across the slope, which meant probing the face semi-horizontally and working towards refusal at each test location.
The road reserve is a narrow corridor with little room for plant, and the testing had to be carried out at an angle to the slope rather than vertically. Obtaining reliable ground condition data in that orientation, within the confines of the reserve, was the central challenge.
Solution
The team abseiled into the steepened road reserve and tested at roughly 45 degrees, perpendicular to the slope face. Because the equipment is carried and operated by hand, test locations could be set up and moved quickly, and seven tests were completed across the site in a single day with minimal impact on the road. The results describe the in situ material across the slope and are being used to inform the remediation design.
Why the PANDA suits this kind of site
A conventional DCP is generally reliable to around one to two metres. Beyond that, friction along the rods increasingly distorts the reading. The PANDA addresses this with an oversized cone and a torque measurement that separates rod friction from cone resistance, giving corrected data at depths and accuracy closer to a CPT.
The energy of each hammer blow is measured electronically rather than relying on a fixed drop height. This lets the operator vary the input to suit the ground, from soft tailings through to very stiff material, using a 1.7 kg hand hammer or a hammering column where more energy is needed. Built-in sensors record resistance, depth and torque automatically, so results are repeatable and free of manual recording error. The output is a penetrogram of cone resistance against depth, which correlates well with CPT data and meets the NF P94-105 compaction standard.
The full kit weighs 18.5 kg, needs no support plant and can be operated by one person at any orientation from vertical to horizontal. Typical investigation depth is four to six metres, with greater depths possible in weaker soils. Beyond steep slopes, it is suited to shallow site characterisation, compaction control and layer verification, confined spaces, and non-vertical testing in tunnels and against retaining walls.
From the Client
“The dynamic probe tool used proved to be a really effective ground investigation method for the site. Challenging access and steep terrain meant more conventional drilling methods were either impractical or would have left us with a lot of uncertainty with the ground conditions. The system enabled rapid investigation across the landslide face, improving confidence in the ground model and helping inform a more optimised, cost-effective, and long-term remediation design for the site.”
Robert Loomes, Geotechnical Engineer, WSP