Tailings being a waste product of mining and quarrying is highly compressible thus tailings dams and ponds are usually undesirable for development. However bigger picture issues such as sustainability and environmental considerations, and demand for land in urban or constrained areas, provide catalysts such that sites once thought of as undevelopable, are being considered for development. The question is, can a tailing storage facility (TSF) be used sustainably and productively after completion of mining? The aim of this paper is to show that it is not only possible, but perhaps now even desirable. Several case studies of sustainable and productive end uses for TSFs are presented and discussed in this paper. A range of technical approaches are demonstrated in site investigations, characterisation of the tailings, and designing ground improvement works to allow reuse. The first case history is a TSF in Western Sydney previously used as settlement ponds in a sand quarrying operation. Converting this TSF for industrial development involved ground treatment using a combination of wick drains and preload, as well as placement of engineered fill over the tailings. Another nearby TSF, is being developed as environmental wetlands which is a very different end use and thus the approach to its development is also very different. In mining, a case study is presented of construction of temporary mine infrastructure including crushing and screening plants, directly on top of an active tailings dam with ongoing settlements, a result of a geometrically highly constrained site. Some ground improvement was undertaken but because mine infrastructure has a relatively short design life and can be more tolerant to settlement, the improvement works were significantly optimised. Collectively these case histories demonstrate a wide range of end uses for TSFs and the corresponding wide range of applicable ground improvement techniques and settlement criteria. The case histories emphasise that the geotechnical engineer needs to collaborate closely with the site owners and developers, and the designers of the future surface infrastructure, to allow TSFs to be repurposed with confidence and achieve sustainable outcomes. In particular we note the importance of all parties agreeing on practically achievable settlement criteria (as part of Landform Performance Requirements) and appropriate selection of the type of infrastructure, such that the repurposing is commensurate with the nature of the site.

Digitisation in geotechnical engineering has potential to further enhance geotechnical analysis and the design process. In this paper, the author will present the general conceptual digital workflows from working examples that have been successfully implemented from recent major project experiences in Victoria. Based on the project experiences from geotechnical interpretation to design, this paper will demonstrate how the integration of digital data on geotechnical projects unlocks improved geotechnical characterisation, increased collaboration, and enhanced visual representation. Additionally, this paper will demonstrate that, in addition to specialist commercial packages and platforms, open-sourced and general-purpose office software packages can also be utilised to achieve similar outcome. Other aspects of geotechnical engineering that can benefit from digitisation in the future will also be highlighted based on the author’s experience.

The important parameters on which the shear strength of any interface depends are overburden stress and degree of saturation. Nowadays, grouting pressure is considered as an another important issue as it provides better interface strength than gravity grouting in case of cast-in-situ soil-cement grout interface, like soil-nail and soil-pile interfaces. In the present study, a series of interface direct shear tests are performed between compacted completely decomposed granite (CDG) soil and cement grout under different overburden stresses, matric suctions and grouting pressures. The interface shear strength envelopes are approximately linear, and the apparent interface friction angle and adhesion intercept increase with matric suction for particular grouting pressures. On the contrary, the apparent interface friction angle decreases with pressure grouting for different matric suctions except saturated condition, at which it remains constant. A mathematical model is proposed for predicting the shear strength of soil-cement interface considering the influence of matric suction, overburden stress and grouting pressure as independent parameters. It is obvious that the interface shear strength predicted from the proposed model agrees well with the experimental shear strength data for different overburden stresses, matric suctions and grouting pressures.

Over the past 15 years or so, access to high quality LiDAR-acquired digital elevation models (DEMs) and powerful geographical information system (GIS) software tools to process and display them, has given geoscientists and engineers a wealth of new ways to tackle geoscience problems. For geotechnical engineers and engineering geologists LiDAR DEMs in GIS have, at a basic level, facilitated the production of accurate, professional site plans and maps. However, more advanced applications supported by hillshade rendered DEMs have opened up a wide range of remote mapping possibilities. The potential for hillshade DEMS to be used as a tool for geological mapping in areas with bedded strata has yet to be fully realised. In some cases, freely-available LiDAR data is sufficient to allow geological structural trends to be established from desktop analysis of DEMs, even when they cannot be determined on the ground, in the field. An example of this is provided. LiDAR DEMs have also proven powerful tools for the identification and spatial mapping of landslides, with widespread use in preparing landslide inventories and hazard susceptibility maps. However, detailed LiDAR DEMs can also be used to understand landslide mechanisms and to classify landslide types. Some examples are provided. In a more niche application, 1 m resolution LiDAR DEMs have proven especially useful in hazard mapping for areas subject to coal mining-induced subsidence, with a demonstrated capacity to reliably identify all pothole features in an area, down to a size of less than 1 m. For difficult areas, such as dense forest, this can be done in the safe and convenient environment of the office, and may give more reliable outcomes than ground-based mapping, which if not undertaken with painstaking diligence, can overlook small features. This paper provides a brief review of the background to LiDAR-derived DEMs, the hillshade visualisation technique, and some of the applications in which hillshaded DEMs have been previously used. It proceeds to present examples as to how these can be used to infer geological bedding trends and structures, infer landslide mechanisms and produce inventories of coal mining-induced subsidence features. Consideration is given to the limitations of this application and the potential to adopt more elaborate hillshade techniques to enhance outcomes.

As the digital transformation agenda extends into underground construction, digital engineering (DE)—enabled by building information modelling (BIM), geographic information systems (GIS), 3D geological modelling and advanced numerical modelling—has become indispensable in the delivery of design and construction processes for major projects. Enhancing visualisation and interoperability of various information sources are particularly valuable in underground construction. Underground infrastructure faces unique challenges due to geological uncertainties and geotechnical considerations where current BIM model view definition has yet been standardised to support the use case of geotechnical analysis. Workflows leveraging heuristic techniques are required toward creating a shared digital representation to aid decision making. This paper explores the expanded use of several DE technologies for tunnel design, construction, and operation. Focusing on BIM techniques such as parametric modelling and key functions of interoperability and visualisation, the paper introduces an interactive platform featuring several workflows. The federated modelling of ground conditions, the as-built environment, and tunnel structures was achieved utilising solid modelling techniques. A graphical user interface was established, enabling the parametric instantiation of segmental linings and crack details with a customisable level of detail (LoD). Through the interface between parametric and numerical modelling, meshed models were created for the numerical analysis of tunnel boring machine (TBM) tunnel excavation and lining installation, groundwater seepage, and long-term structural deformation and ground movement. The work demonstrates a strong potential of advanced information modelling and automated workflows to streamline processes for design, construction and operation stages of tunnelling projects.

The representation of a pile group by an equivalent pier involves significant simplifications, but nevertheless provides a very useful check on the results of more complex analyses of the group. In this paper, previous work on the vertical and lateral responses of an equivalent pier under serviceability limit state (SLS) loadings have been extended to the consideration of the overall stability of the pier under ultimate limit state (ULS) loadings. Approximate expressions for the ultimate axial, lateral and moment resistances of the pier have been adopted, and the stability of the pier has been assessed in terms of a published criterion for foundation failure under combined axial, lateral and moment loads. For this assessment, the computed ultimate resistances have been factored down by a geotechnical reduction factor while various load combinations have been applied to the load components. For practical application of the equivalent pier approach, some correlations for the estimation of the various geotechnical parameters for both SLS and ULS states has been summarized. The simplified equivalent pier approaches, for both SLS and ULS loads, have been applied to the foundation system for the Incheon Tower, for which more complex 3-dimensional analyses were undertaken. The simplified approach gives outcomes that are generally consistent with those from the more complex analysis.

This paper presents a case study of an approximately 20-metre-deep excavation into Bringelly Shale at the St Marys metro station, which is part of the Station Boxes and Tunnelling works for Sydney Metro – Western Sydney Airport. A review of the site geology, ground model and geotechnical design parameters is presented. The swelling characteristics of Bringelly Shale are summarised based on site specific testing results and compared against published data. An attempt is made to appreciate the radial displacement development of ground anchor hole on the bond strength. A coupled groundwater and stress-strain modelling was carried out using Plaxis 2D to optimize the design after anchor pullout testing at the project site. A prediction is made with respect to the ground responses to the retention system using soldier piles and ground anchors during staged excavations. An instrumentation and monitoring plan has been developed and implemented during the construction to validate the performance of the retention walls. The reduced bonded strength of ground anchors in Bringelly Shale with swelling potentials with “weak” rock layers was recommended based on site specific proof testing results. The monitored lateral movement of deep excavation at the St Marys metro station site is ranging between 1 mm to 4 mm per metre of excavation as compared to 0.5 mm to 2 mm per metres for excavations in Hawkesbury sandstone and Ashfield Shale. The findings of this paper are considered to be useful for practitioners who will be involved in future projects dealing with Bringelly Shale having swelling potential.

Bushfires cause immediate disruption to road corridor access and commonly lead to short-term road closure due to debris; however, erosion and landslides can occur after subsequent significant rainfall, which cause far greater long-term disruption to the service levels of the road. Debris needs to be removed and, in some instances, significant slope stability work is required to make the road safe, resulting in prolonged downtime and road network disruption. As a result, communities, emergency services, and key industries including freight and tourism reliant on the network, may experience significant impact. Climate change is expected to worsen the situation; with the frequency and severity of bushfires expected to increase, due to warming temperature, rising drought factor, increased intensity of rainfall, and a greater occurrence of thunderstorms. Infrastructure Victoria’s Adapting Victoria's Infrastructure to Climate Change study showed a 50% increase in the annual probability for loss of life and a 100% increase in direct and indirect costs from bushfire and increased rainfall slope risk under a 2070 future climate for an exemplar rural road in a bushfire prone area (Arup, 2023). While constraints in capital investment for significant upgrades in critical road infrastructure limits the capacity for roads to be immune to bushfires, there is a significant opportunity to reduce the disruption caused by associated bushfire hazards. This reduction then enhances the resilience of the surrounding network and communities. This paper presents an expansion and enhancement to traditional slope risk management practice for roads across Australia to address the impact of bushfires and subsequent landslides on road infrastructure assets in a climate-resilience context. It builds on the nationally applied Transport for New South Wales (TfNSW) Slope Risk Analysis (SRA) framework and integrates climate change and community resilience into the methodology, by assessing variable temporal risk states (current, current with bushfire, post-bushfire, and future climate) and consideration of community risk through consequences based on resilience criteria. The enhancement to traditional practice allows for a more comprehensive understanding of landslide risk considering bushfire with climate-change. The expanded assessed risk levels allow for assessment of proposed mitigation and adaptation measures to support more informed decision making in concert with industry resilience and sustainability strategies where climate is considered in every decision made.

The University of Wollongong New South Wales Landslide Inventory now totals 2,214 landslides, comprising of 148 falls, 368 flows and 1,696 slide category landslides, with 262 landslides mapped in 2022. The extensive rainfall observed in the Illawarra in 2022 has been analysed at extended durations of up to 150 days to determine the effects of combined rainfall events. These effects have been compared to the mapped landslides in 2022 to determine rainfall distribution and landslide movement relationships. Extensive landslide monitoring data has been reviewed to identify relationships between the parameters monitored and landslide performance. The Slide and Flow Susceptibility Modelling has also been updated to reflect the additional landslides mapped in 2022 and it now covers the entire Wollongong City Council local government area.

In recent years, the utilisation of fly ash-based geopolymer has been progressively escalating as it has proven to be a potent alternative to conventional cement. The acceptance of geopolymer is primarily credited to its ability to improve soil strength and stiffness, coupled with the advantage of reducing harmful pollution and energy usage. This study is primarily designed to investigate the mechanical performance of Geopolymer-Treated Crushed Rock Base (GTCRB), with a particular focus on uniaxial compressive strength response and the structural durability quantified by the resilient modulus and permanent deformation. This is achieved through an experimental program incorporating Unconfined Compressive Strength (UCS) and Repeated Loading Tri-axial (RLT) tests. The outcomes of the tests suggest that the use of geopolymer tends to fortify the uniaxial compressive strength and resilient modulus of the GTCRB-tested samples, indicating an overall enhancement in the mechanical properties. Of particular note, a design mix containing 6% geopolymer produced an average UCS of 1.2 MPa, aligning with the standard UCS range for cemented lightly-bound base course material, as specified by the Austroads. In terms of the resilient modulus, while treated mixtures satisfied the requirements for permanent deformation, none of the tested samples achieved the stipulated resilience modulus range.