By 2050, more than two-thirds of the global population will live in urban areas, increasing the need for new transport, energy, and water networks that often can only be built below ground (United Nations, 2024). This surge in demand is transforming the tunnelling industry, pushing engineers to adopt innovative and more adaptive ways of designing and delivering underground works.

The global tunnel construction projects pipeline now exceeds USD 1.26 trillion (BusinessWire, 2025), reflecting both the scale of investment and the growing complexity of the underground environment. Each kilometre of tunnel represents a delicate balance between geology, design and risk. To manage that complexity, engineers and geologists are using data-driven insights to anticipate and manage challenges before excavation begins.

Beneath the surface, a quiet transformation is taking place. Digital tools and adaptive design are reshaping how tunnels are planned, built and managed. The first article in our “Beneath the Surface” series examined risk as an inherent part of tunnelling. This second in-depth analysis explores how digital tools and adaptive design are redefining the discipline, transforming how engineers and geologists anticipate, model and mitigate those risks. Drawing on insights our SMEC specialists will share at the Australasian Tunnelling Conference 2025 later this year, and lessons from projects such as Sydney’s expanding metro network and hydropower developments, this article highlights how high-quality data, rigorous testing and advanced modelling come together to make tunnelling safer, more efficient and more resilient to risks than ever before.

Digital ground intelligence for better decisions

Modern tunnelling relies on continuous, high-quality information about ground conditions both prior to and during excavation. The Sydney Metro expansion spanning more than 50km of twin tunnels running beneath a dense urban environment, is an excellent use case. Lithology changes abruptly across mixed transition zones, making consistent, high-quality data essential for safe excavation and timely support decisions.

Further south, the Snowy 2.0 project, a major expansion of Australia’s Snowy Mountains Hydroelectric Scheme, will add 2.2 GW of generation and 350,000 MWh of storage to the national grid. It requires more than 31km of TBM-driven tunnels excavating through a complex alpine geological environment. Together with the long, linear and deep nature of the project, this means that understanding ground conditions ahead of the excavation is vital for risk mitigation, to highlight any hazards present ahead and to act accordingly (Susilo et al., 2025).

Snowy 2.0’s Tantangara site

To anticipate upcoming conditions in TBM driven tunnels, geologists deploy percussively drilled probe holes up to 100 metres ahead of each cutterhead. These holes allow them to use downhole imaging tools, such as Optical Televiewers (OTV) and endoscopes, to capture continuous colour images of the rock. These images reveal key details like fracture orientation, rock type, and groundwater inflow. This data, combined with daily photogrammetry and face mapping, gives teams an early warning of changing ground conditions. That means less uncertainty and faster, evidence-based decisions about support class, ground treatment, and even TBM operating mode (Susilo et al., 2025).

The Snowy 2.0’s Tunnel Boring Machine 4, named Monica, that will be used to tunnel through the long plain fault zone

LiDAR (Light Detection and Ranging) scanning adds another layer in conventional tunnelling by creating a precise digital record of exposed tunnel faces for design verification. Yet, these technologies do not replace the human expertise. Field geologists still play a vital role. Direct face mapping sharpens geological judgement to distinguish minor lithological changes, stress-induced defects and structural trends that may not be obvious in a point cloud. Their observations, such as subtle colour shifts, moisture marks, or fine fracture textures, often reveal risks long before models confirm them.

Field mapping remains the benchmark for interpreting digital data. Tools like LiDAR and televiewers are powerful, but they work best when paired with geological judgment. Together, they ensure that digital tools enhance, rather than overshadow, sound engineering decisions. (Baxter-Crawford, 2025).

Reliable strength data to underpin design

Accurate ground models are only as strong as the data behind them. Sound tunnel design depends on reliable rock-strength parameters, yet many projects use a limited number of core samples gathered early in development. Variability in laboratory procedures, loading rates and break type logging can shift uniaxial compressive strength (UCS) results by more than 15 percent, a difference significant enough to alter numerical modelling and support design (Chen et al, 2025).

Recent large-scale projects have demonstrated the importance of broader testing programs and rigorous quality control for UCS testing. Although reassessing sample lithology and failure modes do improve data clarity and interpretation, significant variability has also been observed linked to laboratory practices and inconsistently defined loading rates in current standards.

Chen, Zoorabadi, & Stariha (2025) recommended industry-wide discussions relating to the specification of loading rates and stress the importance of laboratory oversight.  Across the tunnelling industry, these lessons are reshaping industry practice. Reliable, well-controlled data allows engineers to design supports that are optimised for safety, efficiency and cost – neither over-built nor under-engineered – and provides the confidence needed to make real-time design decisions underground.

Transformer Hall on Snowy 2.0 

Geology, observation and adaptive design in the digital age

Even with the best datasets, sound engineering judgement remains irreplaceable. Digital tools reach their full potential when paired with strong geological expertise. Sydney Metro offers a clear example: the Hawkesbury Sandstone that dominates much of the alignment includes massive facies capable of self-support and interbedded zones prone to delamination. Thin shale lenses, if overlooked, can trigger shoulder convergence or invert heave, highlighting how subtle geological changes can have a significant impact.

As Baxter-Crawford (2025) observes, industry standards still tend to emphasise broad stratigraphy over lithological detail, increasing the risk of misclassification and sub-optimal support design. Her paper also reflects on the lasting influence of safety reforms following Sydney’s 2004 Cross-City Tunnel incident, which transformed daily practice. While mandatory bolting and structural shotcrete improved safety, they also reduced opportunities for detailed geological mapping, demonstrating the critical balance of digital models complementing field expertise. Experienced geologists working hand in hand with digital validation are essential to keeping the observational method central to modern design, where data informs but human expertise decides.

This balance is highlighted in the “Observational Method for the Deep Powerhouse Cavern Construction of Snowy 2.0 Project” paper, which explains how the design and construction teams implemented an integrated observational framework to manage uncertainty during excavation of Snowy 2.0’s deep powerhouse caverns (Ching et al., 2025). Through field monitoring, 3D numerical modelling and clearly defined trigger thresholds, the team continually compared actual ground behaviour against design expectations. The full cycle of observation, encompassing design, monitoring, re-analysis and response This practical application of adaptive design and digital tools not only enhances safety and efficiency but also demonstrates how data-driven engineering can effectively manage complex ground conditions.

Machine Hall on Snowy 2.0, showing the staged excavation approach with side slashing of the crown excavation

Advanced finite element modelling for safe and cost-effective tunnel design

At SMEC, we specialise in advanced numerical modelling to optimise the design and safety of underground structures. Effective ground support design relies on understanding the actual behaviour of reinforcement elements in practice. A recent study by Emadi and Gomes (2025) on fully grouted rock bolts demonstrates how complex interactions between bolts, grout, and surrounding rock can be accurately captured using cutting-edge modelling techniques.

Using three-dimensional finite element modelling, our engineers explicitly simulated bolt ribs, grout behaviour, and bolt–grout–rock interfaces, incorporating realistic material models and contact interactions. The study revealed key insights into load transfer mechanisms, stress distributions, and failure processes, highlighting how rib geometry influences both strength and ductility. Their model shows that grout cracking initiates at rib corners and propagates into a conical shear band as the steel bolt begins to yield. They also showed that, contrary to conventional design assumptions, a small degree of nonlinearity in the overall behaviour of the rock bolt can still be acceptable. This finding supports more efficient yet safe design by recognising the realistic performance capacity of the system.

With the help of their study, engineers can design beyond conventional approaches by understanding the nonlinear behaviour of rock bolts, enabling more realistic and efficient tunnel reinforcement design under complex conditions. These advanced modelling capabilities allow us to gain insights into the actual behaviour of tunnel reinforcement elements under various conditions, supporting designs that are both safer and more cost-efficient.

Headrace Tunnel on Snowy 2.0 

Integrating data for resilient tunnels

The real value of these innovations lies in their integration. Continuous ground imaging provides early warning of changing conditions. Rigorous laboratory testing delivers dependable rock-strength parameters. Advanced modelling converts this information into practical reinforcement strategies. This feedback loop, together with observation informing design and design guiding monitoring creates tunnels that are safer, faster to build and more resilient.

For governments and asset owners, the message is clear: investing in digital investigation and adaptive design is no longer optional. These methods reduce risk, improve schedule certainty and extend the life of critical infrastructure. For engineers and decision makers, the opportunity is to apply these lessons to future megaprojects and to collaborate with SMEC specialists to tailor these approaches to upcoming projects.

Stay tuned for the detailed technical papers to be released November 2025.

Meet the authors