Using industry best practice to deliver a Geotechnical Investigation for the Spoilbank Marina
The challenge
Following higher than expected tendered quotes from dredging contractors, Pilbara Ports Authority (PPA) asked GHD to review data from a 2019 geotechnical investigation. It was found that the data set could have potentially misinformed Tenderers and led them to include higher contingencies in their pricing for difficult ground/dredging conditions.
Following the review, PPA selected GHD to undertake a new geotechnical investigation for the Spoilbank Marina.
The challenge
GHD undertook a geotechnical investigation to obtain a new geotechnical data set. In just six months, we sourced and engaged the necessary subcontractors, coordinated and executed the field programme, and completed laboratory testing and factual reporting.
Our response
Using GHD’s experience in undertaking projects involving Coastal Limestone in WA, our desktop review of the existing data set identified opportunities for improvement.
We selected a different drilling methodology than previously used for the Project – one that was more expensive but would give us the best opportunity to minimise disturbance of the core during drilling and recovery to provide the best outcome for PPA.
We supplemented the borehole drilling with geophysical surveys, comprising sub-bottom profiling and seismic refraction. The data from both the borehole drilling and geophysical surveys were integrated into a 3D geological model using Leapfrog modelling software.
Strict protocols were applied to the handling, storage and transport of cores recovered from the boreholes. This allowed us to test much more of the core in the laboratory and establish rock strength correlations specific to the site.
Maximising core recovery and maintaining sample integrity were key to the project’s technical success.
The works were carried out just a few hundred metres from the channel of the busiest bulk export port in the world.
The impact
With a comprehensive data set at their disposal, dredging contractors had the opportunity to include less contingency for latent conditions in their pricing.
Hall Contracting was awarded the dredging contract for $21M. Although we cannot attribute a dollar value to the impact of this project, Mr King added “it was a good decision to proceed with the new geotechnical investigation for the project”.
GHD’s data set provided more clarity on ground conditions across the proposed dredging area. This meant tenderers were able to select equipment and methodologies with more confidence, and PPA felt more comfortable relying on the newly acquired data set