An Australian first for dredging site investigation techniques

Site investigations provide the basis of cost-effective designs – or in other words, only with good ground modelling can you get value for money. But not all dredging projects have ground modelling conducted early enough in their lifecycles to realise downstream cost benefits.

More often than not, there’s not enough money allocated to ground studies, and the money that is allocated could be more efficiently used. A good example is when most of it is apportioned to boreholes, rather than the continuous assessment technique designed to test geological heterogeneity (variation) within a site.

The implications can be very costly to a project, especially in the context of outcomes and deliverables on behalf of clients. So how can organisations make the most of site investigations and up the ante on design quality?

Ahead of Dredging & Reclamation 2015, Jason Errey, Manager – Oceanographic Services, OEMG Global, shared exclusive insight into a new technique that is an Australian first from a civil engineering perspective. The company has been developing an Integrated Digital Ground Modelling program, which Jason explains is proving to be a very progressive approach to site investigations.

“We’re just coming out of a big research and development phase for an IDGM, where we take all of the data available, including all of the metadata (such as run lines) and input it into one Geographic Information System based framework.

"From the outset, primary goal of the research program has been to facilitate better communication of complex ground modelling data to all stakeholders of an infrastructure project. We want everyone, including the public, to understand the implications the geological setting has on a proposed structure. To do this, we looked at a number of different software solutions in consultation with our clients,” he says.

OEMG finally settled on Encom PA, which has traditionally been used by mineral exploration companies. But the reason they chose Encom PA wasn’t necessarily because it featured all the capabilities OEMG sought. Indeed, none of the software evaluated did feature them, but because it was written in Australia – in Newcastle and Melbourne.

This meant direct accessibility to the program development team, which has proved very beneficial from a collaboration perspective. And the focus on learning from mineral exploration relates to the primary sub-bottom profiling tool used by OEMG – the Aquares system.

“The Aquares system is wholly developed within our group of companies. Demco is the major IP for the actual Aquares technology, but we are focused entirely on presenting that data to improve the end-user experience, hence – our integrated digital ground modelling program” Jason elaborates.

From its development some 15 years ago, the Aquares system was always designed to provide three-dimensional grids – at that time though, there simply wasn’t enough computing power to generate four-dimensional digitisation outside of mainframe computing. But now, the visualisations produced for clients on laptops are extraordinary.

Eden Harbour ground modelling

Jason and his team team just finished finished a model for the dredging and infrastructure works at Eden Harbour. And in addition to Aquares data, within that model is 30 years’ worth of sub-bottom information comprising:

• Borehole data
• Vibracore data
• Side-scan sonar data
• Magnetometer data
• Reflection data

Interactive chart example, courtesy of OEMG Global

Along with multiple unrelated datasets, the team is able to integrate the information into a centralised GIS framework and allow the design control to view everything within it.

They can also apply their own tests to the Aquares data, because of a subsequent targeted borehole campaign that had been conducted based on geological structures identified by Aquares.

“In the Eden environment there’s a significant portion of vertical or sub-vertical geological structures that are traditionally notoriously difficult to visualise, and then even more difficult to engineer around,” Jason explains.

“We went and identified these vertical structures and then put boreholes both inside and next to them, confirming the Aquares data were reliable.”

As a result, the dredge and engineering consultants can now work on the design based on OEMG’s datasets. It was a successful endeavor for Jason, his team and the principle, because it reduced a significant amount of risk for the project due to the vertical structure mapping.

3D layering, courtesy of OEMG Global

Additionally, through a four-dimensional model, they were able to integrate three-dimensional reflection layers and illustrate the processed reflection layer within Eden Harbour comprised both soft sediment and hard rock.

4D model, courtesy of OEMG Global

“Reflection is a quantitative method, only looking at depth to layer. It has no capacity to differentiate the structural variation within each layer that allows engineers to draw inferences to the implication of those variations. In this case, if you relied on reflection data only or depth to bedrock assessment, you’d be inserting a pile in a geological structure that could vary from soft sand to hard rock. And you cannot base costs or risk on that kind of information,” Jason says.

Government engagement on geophysical data acquisition

In a wider context, for historical reasons refraction data is the preferred qualitative geophysical method, with clients continuing to specify it as a requirement. OEMG recently had high level discussions with the New South Wales State government as to why, because the company has seen a number of contracts come out that have specified refraction.

“In addition to requesting a cost-benefit analysis of past projects, we sought the cost-benefit relationship between different refraction techniques, because a surface-towing refraction cable versus mid-water towing and static refraction setups are very different in terms of outcomes and cost. Even when refraction is specified there’s still no unified method to compare the cost-benefit of each method or indeed alternate methods,” he adds.

GIS applicability

Using GIS to manage oceanographic data isn’t a new concept by any means. Jason first saw it used for this discipline by Statoil and related to the development as a preface for his thesis in 1993.

“GIS modelling has had an interesting introduction. Lots of people questioned early proponents who used Esri’s ARC GIS as opposed to CAD for this functionality, but now we see other major players such as Woodside Petroleum and BHP particularly pushing the Seabed Survey Data Model. So by no means are we the first to drive the concept, but we are pioneering it in the civil engineering space to make it cost-effective and viable,” he observes.

OEMG is currently in talks with the NSW government and Austrade for innovation related to this method, in which funding is being made available to introduce the technology into wider infrastructure-based projects. With access to Aquares technology, the initiative is even more well-placed to take advantage of integrated 4D  and BIM modelling.

I hope you found the article interesting. Jason Errey kindly shared this insight ahead of his appearance at the Dredging & Reclamation Summit in August. If you'd like to know more about the event and his presentation, feel free to download the brochure or visit www.dredgingandreclamation.com.au.