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Use of Geopolymer for Stabilising Crushed Rock Base in Road Pavement
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.
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Waterview Connection Southern Tunnel portal design and construction
The Waterview Connection project comprises 5 km of new motorway in urban Auckland, New Zealand (NZ). The new motorway connects the existing south-western and north-western motorways to complete the Western Ring Route and provide a direct connection between the central city and Auckland International Airport. The project includes twin 2.4km long, three lane tunnels up to 45m deep and retained portal approaches up to 29m deep. This paper focusses on the Southern Approach Trench (SAT) geotechnical design and performance during construction. The SAT was constructed in challenging geological and hydrogeological conditions, with these conditions dictating the design solution. A significant amount of temporary works requirements were built into the permanent structures, such as cement stabilised blocks behind the headwall to facilitate a safe TBM launch and retrieval and allowance for TBM loading on the headwall. Detailed geotechnical investigations, in-situ testing and construction observations and analysis of monitoring data during TBM launch and breakthrough at the Northern Portal facilitated improvements and optimisation of the permanent and temporary works design and will also allow design optimisation of future designs of this nature. -
New tools and directions in offshore site investigation
The offshore environment provides a number of challenges for geotechnical site investigation, among which are the high costs associated with vessel day-rates and an associated need for equipment reliability. New oil and gas developments are increasingly remote, in terms of distance from land and water depths, and seabed conditions often comprise extremely soft sediments within the depth range relevant for infrastructure such as pipelines, subsea foundations and anchoring systems. These factors have combined to provide a gradual shift away from ship-based drilling tools towards seabed-based robotic equipment for drilling, sampling and in situ penetrometer testing. In parallel, a variety of free-fall samplers and penetrometers have been developed, particularly for preliminary investigations to characterise the seabed sediments. An important aspect of the soil response is the extent to which it may be considered drained or undrained during particular operational events. For example, design calculations for the stability and operational movements of pipelines are relatively sensitive to the consolidation response of the soil. Even interpretation of penetrometer data requires an assumption with respect to the degree of consolidation occurring during penetration. The paper provides an overview of recent developments in offshore site investigation equipment, and then focuses on evaluation of consolidation properties.
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Application of Engineering Geological Models
In 2022 the International Association for Engineering Geology and the Environment (IAEG) published version 1.0 of the Guidelines for the development and application of engineering geological models on projects (Baynes & Parry 2022).
The purpose of these Guidelines is to provide succinct, practical, accessible and authoritative advice on the effective use of Engineering Geological Models (EGMs) in a wide range of applications including civil engineering, mining, geohazard studies, offshore studies, land-use planning and environmental assessments. A revision of the Guidelines (version 2.0) was completed in 2024 (Baynes & Parry 2024) and there are also versions of the Guidelines in Traditional Chinese, Portuguese and Spanish. All of these are available as freely downloadable documents lodged on the IAEG website (https://www.iaeg.info/C25EGMGuidelines/).
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Equivalent absolute lateral static stability of on-bottom offshore pipelines
Although Dynamic Lateral Stability Analysis (DLS) is highly recommended for analysing offshore pipeline stability by authoritative recommended practice, namely DNV (2007) and PRCI (2002), it is still limited in its practical applications due to its complexity and because the software required is not widely available. In contrast, Absolute Lateral Static Stability (ALSS) analysis, in which the critical state is that the hydrodynamic loads on a pipe segment do not exceed the soil resistance, is still widely used in industry design. It is usual for ALSS analysis still to be based on the concepts of simplistic Coulomb friction model and the Morrison equation to account for soil resistance and hydrodynamic loading, although both are criticized for their conservatism and less theoretical basis. This paper presents a suite of new design charts with tabulated data using the Fourier method and pipe-soil models based within a plasticity framework for evaluating hydrodynamic loads and soil resistance, respectively. The results are presented as equivalent soil friction factors and hydrodynamic coefficients using the ALSS framework. These can be consulted by pipeline designers to give extra insight into an offshore on-bottom analysis without running the numerically complex DLS.
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Utilising laser scanner and unmanned aerial vehicle (UAV) geotechnical data capture to manage visitor safety in the Buchan Caves
Some of the most impressive limestone cave formations in Victoria are found in the Buchan Caves Reserve. The caves are part of the Buchan–Murrindal cave system, located on Gunaikurnai Land and hosted in a large outcrop of Devonian-age cave and karst-forming limestones. The Reserve is one of East Gippsland’s major tourism attractions, visited by large numbers of local, interstate and overseas tourists annually. Although the caves at Buchan are old (sediments sampled from within the Buchan Caves have been dated at greater than 750,000 years), ongoing periodic rockfalls into the caves, part of a natural process known as ‘breakdown’, are anticipated. The likelihood of breakdown events within engineering timescales poses potential risks to the visitor caves. A Maptek SR3 underground laser scanner and above-ground UAV photogrammetry have been used in combination to capture a 3D spatial relationship between the cave system and ground surface terrain. The resultant digital model assists in visualising this relationship, allowing for accurate identification and mapping of locations where breakdown hazards may be more likely to occur. The model also provides baseline data for future scanning that can help identify and monitor ongoing ground deformation. A geotechnical risk framework has been developed to assist Parks Victoria understand and manage the relative risks posed by cave breakdown, providing a formalised approach to managing safety in the Buchan Caves.
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Failure Processes of Rainfall-Induced Flow Slides Using A Large Scale Model Slope
Flow slides are considered to be universal type landslides as such events are commonly reported in various geological and geotechnical conditions, predominantly attributing mobilised soil flows capable of advancing longer distances at higher speeds. Thus, flow slides are classified as one of the most disastrous landslides. Hence the prior identification of failure mechanism of flow slides is vital in mitigating adverse impacts. A large-scale instrumented model slope was employed to study the failure processes of rainfall-induced flow slides. The model slope was instrumented with pore- water pressure transducers, volumetric water content sensors, digital cameras, and linear variable differential transducers to measure surface displacements. The test was performed on Tsukuba river sand (D50 = 0.55 mm), and the failure behaviour was analysed. The analysis highlighted that the higher moisture contents present in loose soils result in a significant rise in pore-water pressure reducing the shear strength of soil mass. Thus, a sliding surface is generated in the upper slope, and failed slope mass compresses the lower slopes, triggering rapid and catastrophic flow slides. The study concludes that the measurement of pore-water pressure, moisture content, surface displacement, and surface deformation velocities provide notable precursors to rapid flow slides, mitigating adverse impacts of flow slides.
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Railway Engineering And Geotechnical Engineering Are They Married Yet?
Challenges for Geotechnical Engineering in Railways and the gap between research work and the needs and expectations of Rail Operators.
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State Highway 16 Causeway Upgrade – Motorway Widening Design Over Soft Ground and Post Construction Monitoring Verification
The SH16 Causeway Upgrade Project in Auckland, New Zealand forms part of the overall Western Ring Route Project, an alternative to Auckland’s State Highway 1, linking Manukau, Auckland, Waitakere and the North Shore, improving network resilience, and travel time reliability. The Causeway Upgrade was procured as an alliance due to the complex technical and environmental nature of the project. The project route is constructed over soft marine sediments. The Causeway Alliance team compared ground improvement alternatives during the tender and design phases and selected, designed and constructed an innovative wick drain with preload option. Monitoring of a New Zealand Transport Agency (NZTA) trial embankment was also carried out from the end of its construction and the ground model and material parameters were further explored. A wick drain and surcharge program was designed to achieve settlement requirements, and consolidation settlement back analysis was carried out to compare with the ongoing performance to allow refinement of the surcharge and wick drain design. Comprehensive numerical analyses were also carried out to assess road embankment stability and consolidation deformations. Post construction performance assessment and monitoring have also been carried out. The design and construction have been shown to be a cost effective and technically achievable solution, which is best situated to the existing ground conditions. This paper summaries the key components in the analysis development and outlines innovative soft ground improvement design and construction carried out at the Causeway.
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Slope Risk Analysis Supporting Post-disaster Recovery: The 2016 Kaikōura Earthquake
On 14 November 2016 a M7.8 earthquake caused significant localised damage to transportation infrastructure around Kaikōura, NZ. The strong earthquake-induced ground motions in the near-source region resulted in substantial rockfall, translational landslides, and channelized debris flows. The closure of SH1, the Inland Kaikōura Road and the Main North Line railway effectively cut off all land routes into Kaikōura.
The North Canterbury Transport Infrastructure Recovery Alliance (NCTIR) was established to rebuild and reopen the coastal routes. To better understand current and future risk to road users, slope risk analyses were carried out following the NSW Roads and Maritime Services 2014 Slope Risk Analysis methodology (NSW RMS SRA 2014). Various risk scenarios were considered reflecting the temporal change in hazards, likelihood, and consequences through the post- disaster recovery process. The core approach of the NSW RMS SRA methodology was applied to consider multiple risk scenarios in order to support the post-disaster activities. A total of ~70 slope risk analyses were carried out over 10km of SH1. Due to the large spatial extent of the slopes and source zones, automation of geospatial analysis of LiDAR derived digital elevation models increased efficiencies in the analysis and documentation.
The application demonstrated that rapid post-disaster risk reduction practices like traffic control and temporary barriers were effective in temporarily reducing risk to acceptable levels. The NSW RMS SRA can be used throughout the post- disaster response and recovery process to understand risk to road users in re-opening the road and optimise the balance of proposed risk mitigation options between risk reduction, costs and impact to road users.