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AGS Adelaide Symposium 2023
Novel Solutions in Sustainable Geotechnics
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Managing mine subsidence along railways and highway pavements in the Southern Coalfield
There is a long history of underground coal mining in the Illawarra, dating back to the mid-1800s. In recent times, coal mines have worked closely with the owners and operators of both private and public infrastructure to mine directly beneath infrastructure whilst maintaining their safe operation. An overview is presented of recent methods that have been used to successfully manage potential mine subsidence impacts on railway and highway infrastructure, whose presence in the past necessitated sterilisation of coal resources. Some of these methods represent βworld firstβ technology and have applications beyond the field of mine subsidence management.
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Unsaturated Soil-retaining Wall Interaction: Experiments And Theoretical Modelling
In this paper experimental observations and theoretical modelling outcomes are presented which show the significant effect suction has on the interaction between unsaturated soils and retaining walls. Firstly, a new testing facility and set of procedures for performing retaining wall model tests in unsaturated soils are described. The facility enables a rigid model wall to be rotated into or away from a soil sample about its toe. Results for samples of unsaturated decomposed granite are presented. Suction changes were measured using vibrating wire piezometers. Pressures on the wall were measured by earth pressure cells embedded in the wall face. Integrating the earth pressure profile enabled an equivalent load acting on the wall to be calculated, and was in reasonable agreement with the measured applied load. Soil deformations were recorded using particle image velocimetry. The pattern of soil deformation observed, particularly strain localisations, was similar to those in tests on dry sands. The suction increases measured during the test were consistent the volumetric dilation that occurred in the sample. Secondly, an extension of slip line theory to unsaturated soils is presented and applied to the rigid retaining wall problem. Suction is introduced using the effective stress concept. The predicted effective normal stresses were found to be in reasonable agreement with experimentally measured values.
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A soil mechanics study into the liquefaction of shipped metallic ores
The transport of iron ore and other metallic ores by sea has been of increasing concern in recent years as several ships, their valuable cargo and around 200 lives have been lost because of liquefaction of the cargo. This has led to extensive soil mechanics based testing and analyses into the behaviour of iron ore fines during shipping transportation. In particular, the use of the Transportable Moisture Limit (TML), the maximum allowable moisture content based on a modified Proctor Fagerberg Test (PFT) at which a material is designated as being at risk of liquefaction when loaded into bulk carriers, has attracted considerable interest. The International Maritime Solid Bulk Cargoes (IMSBC) Code has categorised iron ore fines as a problematic cargo, prone to liquefaction because of the presence of moisture as well as fines in the material. The IMSBC code uses the TML to prevent liquefaction of the cargo, however, the rationale behind using the TML has been questioned.
This study investigates the influence of fines on the mechanics behind the liquefaction of well graded materials with similar gradings to iron ore fines that could be expected to liquefy during shipping transportation. The results so far show that as the fines content is increased, the density achieved during the loading of the material onto the ship decreases. However, results from cyclic triaxial tests suggest that density alone is not a good indicator of how resistant a material is to cyclic liquefaction. Using the state parameter gives a better understanding of the overall behavioural trend of the materials when subjected to cyclic loading conditions. The influence that these findings and results from preliminary unsaturated cyclic triaxial testing has on understanding the liquefaction behaviour of ship cargoes, will also be discussed.
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Queensland AGM and Annual Symposium
Recent advance in geotechnical engineering, engineering geology, and testing
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Fatigue performance of asphalt with different conventional binders
A series of experiments has been conducted at Curtin University, Australia to explore the influence of different conventional binders used in asphalt mixes on their fatigue performance. Fatigue cracking is one of the key distress modes occurring in flexible pavements. The different binders used in this research differs in viscosity. Through this study, results showed that the flexural stiffness decreases as the repetitive load cycles are applied. Results in this study also show that the fatigue life varies with the increase of viscosity of binders used in the asphalt mix. The fatigue life found in this study decreases from Class 320 asphalt mix to Class 170 and then Class 600. In addition the tests were carried out in a constant temperature, strain level and loading frequency. In this research, the fatigue life of asphalt mixtures with different conventional binders was evaluated through a four point bending test in strain controlled mode and with harvasine loading. The fatigue life of the asphalt mixtures has been assessed and determined based on the 50% reduction in the initial flexural stiffness.
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Development of Computer Code to Optimise the Production of Hydrographs in Sydney, Australia
Long term groundwater level monitoring has been conducted in support of the environmental impact statement (EIS) prepared for the WestConnex M4-M5 Link project (RMS, 2017). The M4-M5 Link will connect two predominately underground twin drained motorway tunnels and multiple interchanges which will be excavated from the Hawkesbury Sandstone and Ashfield Shale. In order to assess the impacts of the tunnels and associated infrastructure on the local groundwater systems, a groundwater level baseline data set is being developed to characterise natural seasonal and tidal variations in the existing hydrogeological regimes.
A network of data loggers have been installed in groundwater wells screened in alluvium, Ashfield Shale and Hawkesbury Sandstone and are programmed to monitor groundwater levels through hydrostatic pressure fluctuations at an hourly interval. Barometric monitoring was also undertaken to correct for atmospheric pressure variations. Due to the large amount of data generated by the project and the shortcomings of Microsoft Excel as a streamlined graphing tool, innovation was required on the traditional method of using Excel for data analysis. As such, a custom R code was created to automate the process of hydrograph generation. The code imports folders of raw data logger files, barometrically corrects the data, identifies the groundwater well location of each raw data logger file, matches each file to the manually recorded standing water levels, and converts the groundwater level to m AHD from the raw pressure files. The code then produces hydrographs, plotting the reduced standing water levels against rainfall, exporting a fully formatted combined PDF of each hydrograph. This process significantly reduces the time spent on data manipulation and graphing and the potential for human error during the data manipulation phase.
This visualisation of the data has allowed groundwater trends within the measured time to be observed, including the tidal and rainfall dependant nature of recharge. In the Hawkesbury Sandstone, groundwater fluctuations shown in the hydrographs display a high correlation with rainfall patterns observed over the monitoring period. The alluvium is primarily controlled by local recharge and discharge conditions within the measured time. Several hydrographs also show tidal oscillations, suggesting hydraulic connections with nearby canals, creeks and Sydney Harbour. The creation of this data processing code has greatly reduced the time required for data manipulation in assessing groundwater patterns in the area of the M4-M5 Link WestConnex project. For other large groundwater monitoring projects, investing time early in the development of data processing codes could add similar benefits.
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Collaboration In Finding Alternatives To Lime Stabilisation Of Reactive Soils
Sustainability has been an active theme in recent years in the Australian construction industry and various specialist publications have highlighted the fact that everyone in the industry has a role to play.
This paper outlines the collaboration work involving geotechnical engineers from EIC Activities, a senior civil engineer from CPB Contractors, both members of CIMIC group, and academics from the University of Western Sydney to create a sustainable and reliable alternative for the stabilisation of reactive soils. It will provide an overview on the various stages of the collaboration from an initiative to reduce lime in concrete, that was the genesis of the idea, up to the recently submitted ARC linkage grant between the University of Western Sydney and the CIMIC Group. The focus on sustainability relates to lime, reactive soil, and the authorsβ attempt to contribute in a sustainable and productive geotechnical practice. Detailed technical accounts will be provided at the various stages of the collaboration.
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Case Study Of Railway Embankment Stabilisation Works At Moor Park Station With Progressive Slope Failure
Two railway embankments which are located next to Moor Park station, approximately 30 km northwest of London, support the southbound and northbound London Underground Metropolitan Line tracks. The embankments were identified as showing various signs of progressive slope failure and required implementation of stabilisation works. The earthworks originally constructed in the late 19th century were subject to embankment widening works in the 1940s and have had a complex history of construction and modification with evidence of past instability.
For the remedial works, there were a number of geotechnical and construction issues which included highly variable ground conditions, environmentally sensitive sites surrounding the embankments including a man-made river and existing rail structures along the embankments. This paper describes the measures taken to manage the geotechnical risks.
The adopted design criteria, the slope stability assessment and the proposed remedial works which include a bored pile wall with precast concrete capping beam, a discrete bored pile wall, a slope regrade and toe berm are presented in this paper. For the design and slope assessment, modified soil strength parameters for high plasticity index cohesive embankment fill or weathered London Clay identified from soil investigation was used.
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Parametric Study On Behaviour Of Reinforced Soil Walls With Combined Horizontal And Vertical Geosynthetics
The reinforced soil system employing geogrids, as a cost effective reinforcement technique, has come to play an important role in a variety of civil and geotechnical engineering applications. In regular reinforced soil walls, the reinforcements are usually laid horizontally in the soil. In this study, the behaviour of reinforced soil retaining walls with combined horizontal and vertical reinforcements are investigated experimentally as well as numerically. The results, indicating the effects of vertical reinforcement inclusion, are compared to conventional reinforcing types under static and dynamic loads. The performance of retaining walls employing vertical reinforcement in conjunction with horizontal reinforcement is convincing from the results of the shake table tests conducted by the authors. In this paper, PLAXIS, well-known geotechnical software, is used for conducting a series of parametric studies on behaviour of reinforced soil walls under construction and subject to earthquake loading, incorporating the vertical reinforcement. The vertical reinforcement layout and its strength are among the major variables of the investigation. The geometry of the model, soil properties and reinforcement characteristics have been kept identical in all different cases selected for parametric studies. The performance of the wall is presented for the facing deformation and crest surface settlement, lateral earth pressure, tensile force in the reinforcement layers and acceleration amplification. The vertical deformation, horizontal deflection, reinforcement force and earth pressure develop drastically under earthquake loading compared to the end of construction. The results show that these variables are considerably reduced when incorporating the vertical reinforcement in the system. In addition, the findings suggest better performance and higher structural safety for reinforced soil walls, when employing this proposed orthogonally horizontal-vertical geosynthetics.