From a geotechnical perspective, a digital twin can marry the worlds above and below ground and reveal their interactions. Integrating a geological 3D model with a structural 3D model (e.g. physical building or tunnel) unlocks a more detailed and powerful picture of how a structure sits on and in the ground. When we can see how an aboveground structure looks when wedded to the geological conditions underneath it, we can better understand where the risks lie and how the structure is likely to perform. Interactions between the models can provide real value and potential savings. The combined picture will also more clearly communicate project risks. This “new whole” is much bigger than the sum of its parts.
It’s exhilarating to witness the digital evolution in physical sciences, but this technology delivers more than just pretty pictures. The real value in digital twins is in improving project delivery by allowing us to better understand risks, produce safer and more efficient designs, and communicate more effectively with all project stakeholders.
Digital twins in the real world
A ‘digital twin’ can be described, for the purpose of this article, as a 3D representation of a design, or physical object, that includes current ground conditions and planned or constructed infrastructure.
Consider a project that requires excavation through complex terrain comprising different geological units in cross-cutting relationships. Such terrain cannot be well characterised or represented by 2D sections. However, with a sufficiently large database and a 3D understanding, we can better discern and communicate these complex relationships. We can generate information that better characterises the ground and provides a better appreciation of risks and uncertainties. Taking information into 3D doesn’t take uncertainty away, but it does reveal where there’s data, or a lack of data, so that the level and areas of uncertainty can be better understood and, if necessary, further investigated.
Now, to create a digital twin, we can combine this 3D geological model with structural data including subsurface infrastructure. This offers increased accuracy and reduced uncertainty so that we can better plan how the asset will be built, and what it will take to build it. For example, we can estimate the effort required to excavate a rock mass from a basement dig, or how much acid sulphate soil we’ll need to treat from a tunnel excavation.
When ground conditions are variable, such as in a fault zone with variable weathering and fracture, it is easier for the stakeholders involved to understand the implications of the ground conditions when they are represented in a digital twin. The combination of the structural and geological models demonstrates “backwards and forwards effects” and compatibility. Using this approach, we can better characterise the risk for all parties and communicate the risks earlier in the project, avoiding the unwanted geological surprises that can occur in infrastructure projects. The digital twin paves the way for a smoother, quicker project.
Understanding risk and optimising design
Even on a site where geological conditions are relatively uniform, there are risks. When the site is complex, it’s important to understand what the key geotechnical issues are, where they occur, and what combinations of factors lead to the ‘critical’ location for any proposed infrastructure construction. This is the key to a safe structural solution that is optimised to the conditions present but not overengineered unnecessarily.
Take the example of building a large structure on a complex geological formation including intrusive dykes. When fresh, these dykes have the density of a granite but change to a lower-density clay when weathered, which can cause a stress to develop in the rock mass. The ‘locked-in stress’ can be inadvertently relieved when excavating nearby, which can be dangerous. These ground conditions are unlikely to perform adequately for engineering purposes, so it’s essential to try to understand how the dyke will interact with the overlying structure. How will the ground respond when we excavate the basement and put the structure on top of it?
Combining a 3D understanding of the geology with the structure as it is intended to be built, we can start to understand which complexities in the ground conditions apply and which aren’t relevant. It becomes apparent where footings and foundations may need to be redesigned to avoid inadequate bearing capacity or excessive settlement over poor ground conditions, or where they could be optimised (such as changing from a pile to a pad footing on favourable ground conditions). It also demonstrates where the retention system design may need to be modified or strengthened to accommodate the non-uniform behaviour of the rock mass. Variable ground conditions may have significant implications for a range of specialist contractors in terms of construction techniques and equipment.
Here to stay
Opportunities for digital twins are everywhere. With the decreasing cost and time involved in building and combining the 3D models coupled with rapid progress in software capabilities, digital twins are becoming feasible on small projects as well as large ones. For example, combining 3D contamination models with 3D geological, structural, and computer-aided design (CAD) models can support a much better understanding of how much contaminant mass may need to be removed from a brownfield site during remediation. We can also use a digital twin to explore ‘what if’ scenarios and test out alternative designs.
It is important, though, that the digital twin is not seen as an oracle or the repository of all truth, wisdom, and knowledge. A model is only as good as the data that created it, so it’s essential to remain aware of the limitations. The twin is also only useful so long as it remains ‘alive’ – accommodating new data as conditions change. If new ‘real world’ information isn’t fed back into the digital twin, it will become obsolete at a minimum and potentially misleading at worst.
In a rapidly changing world, it’s time for geologists, engineers, and structural designers to put on a digital hard hat and get to know digital twins. This technological leap offers many exciting new possibilities for safer and more efficient design, and for better understanding and communicating risks, opportunities, interactions between technical specialists and project leaders, and uncertainties. When it comes to bringing worlds of information together, the use of digital twin technology is breaking new ground.
ABOUT THE AUTHOR
Michael Webster is a senior engineering geologist, based in Melbourne, Australia. He has undertaken 3D modelling for many projects across Australia. Michael has built models ranging in size from 500 m2 to 500 km2, for projects such as road and rail tunnels, high rise developments, landfills, dams, contaminated land remediation and geotechnical due diligence.
