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Postscript to the closure to the discussion of “Assessment Of The Coefficient Of Consolidation With Queensland Data”
This paper presents a postscript to the closure to the discussion of “Assessment of the coefficient of consolidation with Queensland data” by Burt G. Look. https://doi.org/10.56295/AGJ5846.
The Discusser thanks the Author for providing a detailed Closure touching on several aspects of soft soil consolidation. However, in contrast to the Discussion the Closure (and Paper before it) had no long-term, independently (or at least able to be) validated case histories supporting the claims made.
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A new ring shear apparatus for the determination of the residual shear resistance of remoulded brown coal
Victorian brown coal is a typical intermediate geomaterial, whose behaviour falls between that of soft rock and engineering clay. The intact material exhibits lower permeability and higher tensile strength compared to overconsolidated clay. Large, shallow open cuts are used to mine the coal in the Latrobe Valley, Victoria, Australia, predominantly as fuel for Victoria’s power stations. For batter design the brown coal is treated as clay with high values of cohesion and friction angle. Composite rotational and block sliding is a recognised failure mode for this material and it is apparent from recent observations that failure risk increases with time. During long-term movements of the brown coal behind and below the batters it is anticipated that the material will be crushed and remoulded along sliding surfaces as a result of progressive pre-failure displacements. After periods of decades, the assumption is that for large sections along any incipient failure surface, shear strength will be at or close to the residual shear strength of the material. Thus. it is important to understand whether this assertion is correct and the processes leading to the weakened state. A new ring-shear test apparatus has been designed to determine the variation of shear strength of this material for a range of shear strains under essentially drained conditions. In this paper the design considerations and the resulting form of the test apparatus are presented. The equipment is also applicable to the testing of the interseam clays, silts and fine sands that are also found in the mines.
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Ground Control For A Deep Basement Excavation In Sydney’s GPO Fault Zone
The use of the underground space in major cities often involves complex systems with significant interaction between new excavations and existing structures such as buildings, services and tunnels. Such a complexity significantly increases when excavating in poor quality or unstable rock masses. Such ground conditions can be found in a fault zone or areas with high locked-in horizontal stress, both commonly observed in Sydney. This paper presents the geotechnical design challenges and construction outcomes of a deep excavation for a 38-storey mixed-use tower with 3 basement levels in the Sydney CBD. The challenges included excavating in the immediate vicinity of heritage listed buildings and rail tunnels built circa 1930. Two distinct excavation zones were inferred during the geotechnical site investigation, including both poor rock mass related to the GPO fault zone and good quality sandstone. An additional challenge was imposed by a 14 m deep excavation of a vehicle lift shaft with unsupported horizontal spans of 10 m, i.e. without internal support such as anchors or struts. Details of the design approaches and methods of analysis are discussed. These included a 3-Dimensional (3D) finite element (FE) analysis for prediction of ground movements and impact assessment. A structural frame model was used to simulate the effects of waler beams in 3D; hence it could be used as an input in the 2-Dimensional (2D) finite element model of the excavation. Finite Element Limit Analysis (upper and lower bound theory) was also adopted to estimate global factors of safety. A comparison between Class A predictions of ground movements developed during design and impact assessment stages and onsite measurements taken during and after excavation will be discussed. These include field data from two inclinometers, one horizontal extensometer installed in the vicinity of the rail tunnels and survey targets around the perimeter of the excavation. Photos taken during construction are presented to illustrate the challenges and successful outcome. These include some snapshots of the GPO fault zone, completed excavation with multiple ground support and ground control measures.
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Earthquake Hazard And Risk In Regions Of Low To Moderate Seismicity
Historically building design in many parts of world does not consider seismic loading. While this is clearly not appropriate for regions of high seismicity it is probably sensible for regions of low seismicity. The question addressed by this paper is whether the cut-off level for seismic design as proposed by the US International Building Code (IBC) is reasonable.
This paper presents some key issues regarding the nature of seismic ground motion hazard and how to assess whether it is sufficiently large to require it to be considered in the design of buildings. It begins by summarising some observations from the 1985 Mexico City and 1989 Newcastle earthquakes with regard to building damage and site response effects. These observations are followed by an overview of seismic hazard and risk studies carried out by the author for the United Kingdom, Hong Kong and the Malay Peninsula. These studies were carried out in the early 1990’s, 2000’s and 2008 respectively. Partly because of this range of timing, and the widely different nature of the building stock, the methodologies used for these studies have developed. The underlying results however show that the IBC gives reasonable guidance as to when seismic ground motion can be ignored.
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A web-GIS and landslide database for South West Victoria and its application to landslide zonation
The Australian Geomechanics Society’s (AGS) guidelines on Landslide Risk Management emphasise landslide zonation as a key requirement for regulators dealing with landslide risk (AGS 2007a). The basis for zonation is a landslide inventory which reflects the nature and spatial distribution of landslide types in a particular locale, such as a local government area. This paper describes the design and implementation of a web-based landslide database for south west Victoria aimed at disseminating landslide inventory information to regulators, consultants and the general public. Although the 4,581 mapped landslides represent the most complete and extensive data set for the region, the current data quality and resolution does not meet the AGS guideline for landslide zonation at the municipal planning scale. However, with an essential need for landslide planning controls in this region, the data is the best available for the construction of zonation maps, resulting in conservative boundaries at the required map scale. The paper highlights the ongoing need to improve the spatial extent and quality of the landslide database if the statutory planning zonation maps are ultimately to comply with the AGS guidelines.
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Pull Out Resistance Of Geosynthetic Straps From Shale And Silty Sands
This paper presents results from a study of the pull out resistance of geosynthetic (ParawebTM ) straps from two fill materials. The first is sand with variable silt contents and the second is Ashfield Shale. For both materials shear box tests of the fill material, shear box interface (fill material – geosynthetic) tests and pull out tests have been performed for a range of confining stresses.
There has been evidence of the poor performance of reinforced shale fills in Sydney, but the reasons for this are not well understood and many different opinions exist. These include weathering/breakdown of the shale, wetting/pore pressure development, creep and arching. Tests have been performed to evaluate which of the proposed mechanisms is responsible for the poor performance. It is shown that the tendency for even well compacted shale to compress when sheared contributes to arching, which leads to low pull out resistances. It has been found that when the shale is crushed to <75 m the pull-out resistance is greater than when a uniform material with gravel sized lumps is used. This is explained by the arching mechanism and the impact of the grading on the stiffness, density and compressibility of the fill material.
It is widely accepted that reinforced earth walls (REWs) need to contain ‘good quality’ fill i.e. sands and gravels that are well graded. For example, the RTA QA specification R57 (2007) states that soil properties should be granular and contain less than 15% fines <75 m. Tests have been performed to assess the effects of increasing non-plastic fines content by mixing silt with sand. Addition of silt affects maximum and minimum densities, frictional and dilatational characteristics and the pull-out resistance. It is shown that addition of non-plastic fines significantly improves the pull- out resistance for low fines contents and as further fines are added the pull-out resistance reduces. However, even with 26% fines the pull-out resistance is greater than for clean sand.
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Shear Strength and Modulus of Mine Waste Rock – Large Scale Laboratory Testing Results
This paper presents the sampling and laboratory testing results of mine waste rock consisting of limestone, siltstone, and intrusive materials collected from the Ok Tedi open pit mine in Papua New Guinea. The laboratory tests included specific gravity measurements, index testing, large-scale direct shear tests using a 720 mm square direct shear apparatus, large- scale consolidation tests using a 550 mm diameter consolidation apparatus, and shear wave velocity tests conducted on compressed waste rock samples. The obtained strength values, as well as small and larger strain modulus values, were subsequently compared with existing literature data from the literature. These findings can serve as a valuable reference for mine waste materials with similar lithology, particle size distribution, and stress condition, particularly in the context of static and seismic slope stability designs.
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Responses Of Free-Standing Railway Embankments As A Consequence Of Mine Subsidence In The NSW Southern Coalfield
To support our civilisation’s requirement for carbon steel, longwall mining of the Bulli Seam at Appin and Tahmoor Collieries has occurred to recover high quality coking/metallurgical coal, being for steelmaking. The Main Southern Railway crosses the footprint of both mines, and it was therefore important to manage the risk to infrastructure and public safety during longwall retreat in this strain-driven environment. One technical issue is the response to subsidence-induced ‘valley closure’. This has occurred in both gently undulating Wianamatta Group Ashfield Shale and the steeper upper Hawkesbury Sandstone valleys.
This paper covers the observed responses of embankments on the Main Southern Railway and the heritage railway Picton to Mittagong Loop Line, and illustrates the responses of the embankments to valley closure that produced up to 11% strain, as well as illustrating displacement field development and derived principal strain vectors. The responses of four embankments are presented beneath which longwalls have been successfully extracted, and done so without adverse impact upon public safety. An understanding of the strain-driven responses of the embankments is presented.
This paper is adapted from and builds upon a submission to 11th Triennial Conference on Mine Subsidence – refer to Leventhal et al (2022).
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Design and Installation of Mobile Offshore Drilling Unit Mooring Piles Using Innovative Drive-Drill-Drive Techniques
The North West Shelf, which is Australia’s largest offshore oil and gas province, is well known for the engineering challenges posed by the calcareous seabed sediments present and its exposure to extreme weather associated with tropical cyclones. Mobile and fixed platforms are used to tap into the hydrocarbon reserves and these need to be secured to the seabed using substantial foundations and anchors, which must resist onerous cyclic loads. This paper describes a project where an innovative drive-drill-drive installation approach was adopted to enable the installation of twenty-four anchor piles to moor a mobile offshore drilling unit (MODU) at two drilling sites. The two sites encompassed a wide range of complex seabed geologies, from high strength limestones to uncemented silts, where conventional drag anchors or driven anchor piles would not prove entirely suitable. Installation was carried out using a dynamically-positioned vessel, oper- ated by Fugro, on which an inventive purpose-built drilling tower had been erected specifically for the project. The in- stallation also included development and deployment of an ingenious seabed frame that could grip and release the piles progressively, plus casings to temporarily stabilise the drilled holes from collapsing sands. This project provides an ex- cellent example of how multidisciplinary collaboration can embrace innovative solutions to successfully deliver complex projects safely, on budget and to an accelerated schedule.
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Hoover Dike USA – Experiences with the use of a digital twin in specialist civil engineering
Clewston, USA. Paper is outdated, the digital twin is reality!
This is how evaluations and production optimisations run in a matter of seconds in digital form. The customer is aware of that as well and that is the reason why the customer demand data management on the Herbert Hoover Dike contract. Production parameters are recorded every second by the CSM rig using various sensors and saved in a production file. In addition, all project-relevant data (reports, images, videos …) are stored centrally and are made available for the customer on a daily basis. All project parties have the possibility to follow the process of the construction site on a digital replica and are able to start control measures for the execution or planning.
The production data are read into the relevant production data management system “b-project”, processed, and stored in a standardised database. The production logs, quality checks or overlap calculations generated from this twin are created completely automatically by b-project. The overlaps between the individual constructed Cutter Soil Mix (CSM) elements are required by the customer in three different levels and every 10 feet (approx. 3 m).
No 2D/3D modelling software or other programs are required for the visualisation and calculations. The data and tools are implemented in the software. A data manager sets up the system on the construction site and raises an alarm if there are any quality defects. As a result, location-independent control measures can be initiated in the shortest possible time after the element has been manufactured. All data can be accessed worldwide. In this way, the efficiency of the measures initiated can be traced directly on the digital twin.
A 3D geographical information system (GIS) system opens another form of visualisation and documentation for the digital image of the project. This enables a uniform understanding of the project and visual monitoring of target/actual states.