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Thredbo Lessons – Part 2
I was the Coroner’s Adviser on the Thredbo Disaster, a role that filled a large part of three years of my life. Over the past couple of years I have been giving lectures on Thredbo emphasising the technical lessons for the profession. However, in addition, there were also numerous more personal experiences and lessons, including the joys of 22 days in the witness box being minutely examined by seven different parties.
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A Novel Multiple-liner Design For Preventing Desiccation Of Geosynthetic Clay Liners
Geosynthetic clay liners (GCLs) covered by geomembranes (GMB) often constitute a major component in barrier systems. They are used in waste containments systems such as landfills, brine ponds and solar ponds. In many of these cases, high temperatures can develop as a result of exothermic biodegradation or direct solar radiation and can cause significant desiccation of the bentonite in the GCLs. In addition, the self-healing ability of bentonite may be compromised by exposure to chemically aggressive permeants that are commonly found in such applications.
A new multiple-liner design is proposed in this paper, with two GMB-GCL composite liners sandwiching one layer of geocomposite (GC). The new design is able to actively hydrate top and bottom GCLs through the middle GC layer with clean water. A set of column model experiments simulating a typical bottom profile under a brine pond were conducted to investigate GCL hydration before and after continuous heating at 78±1oC for 14 days. The results were compared to the more conventional GCL-GMB designs. The findings revealed that the new multiple-liner system speeds up hydration of bentonite in the GCL by a factor of more than 3, increase its water content at the end of the hydration stage by up to 50%, and prevent its desiccation when exposed to high temperatures.
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Saturated-unsaturated flow and solute transport in engineered liner systems: A new special-purpose finite element analysis software
Engineered liner systems are widely used in various types of waste repositories such as municipal waste landfills, leachate ponds, remediation sites and solar and brine ponds. Designers, practitioners and regulators often need to assess the ability of actual or planned liner systems to perform their function adequately over a long time scale dictated by the slow transport properties in low-permeability soil. The flow and chemical transport equations, either independently or in coupled mode, under either saturated or unsaturated conditions, need to be solved, while incorporating complex liner details in the simulation. General-purpose finite element software able to solve these equations often are cumbersome when analysts use them to build liner systems. This paper presents a new finite element software system developed at the Centre for Geotechnical Research of the University of Sydney over the last 5 years. The software, called Soil Pollution Analysis System (SPAS), has been designed to simplify the model-building process of liner systems, while allowing for a range of flow and transport problems to be simulated in 2D and 3D. SPAS is able to solve 28 different types of coupled or uncoupled problems for water flow and single-phase, multiple-porosity chemical transport, in saturated or unsaturated media, under steady-state or time-dependent conditions. A powerful feature of SPAS is its ability to seamlessly model coupled problems in which the transport of chemical species depends on highlyheterogeneous water seepage velocity fields. Processes such as biological, radioactive or chemical decay, diffusion, mechanical dispersion, advection, sorption (linear or non-linear, instantaneous or time-dependent), multi-layering and interface partitioning can all be represented in the model. In unsaturated soils, a range of commonly used soil water characteristic curves is available. The software has been extensively validated and optimised and, in 2D, typically computes the full history of flow and contamination, in less than five minutes of computing time on a Windows-based personal computer with an i5 Intel processor.
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AGS SA-NT Annual Seminar 2018
Design and construction of earthworks and pavements on expansive clay
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Advances in Ground Monitoring Techniques – A Surveyors Perspective
In essence ‘Surveying’ is simply the science of measuring positions on Earth. Surveying has been a key element in the development of the human environment since we stepped out of the caves. The relationship between surveying and geotechnical engineering principles arguably dates back just as far. There is a real synergy between these disciplines / professions that, in the main, is often not fully appreciated.
The core mathematical foundations upon which surveying is based are essentially unchanged. What has changed enormously over the centuries and dramatically over the past decade or two are the technologies available to Surveyors to aid them in measuring the ‘Earth’, and anything built on / in it.
This paper touches on a range of current survey measurement methodologies, some of which may be considered ‘tried and true’ traditional techniques along with a number of exciting newer technologies such as LiDAR (Light Distance and Ranging), DInSAR (Differential Interferometric Synthetic Aperture Radar), GNSS* (Global Navigation Satellite System) based real-time 3D measurements, with particular attention given to drone (Unmanned Aerial Vehicle – UAV) based digital photogrammetry.
Like many measurement techniques, digital photogrammetry is a technological evolution of a well understood and developed traditional analogue approach. With the advent of laser scanning (LiDAR) measurement technologies in the late 1990’s, analogue photogrammetry rapidly fell out of favour for all but a few niche measurement applications. However, over the past few years there has been a dramatic shift back to ‘digital’ photogrammetry. This re-emergence has been facilitated by advances in digital photogrammetry autocorrelation algorithms, increases in computing power, relatively affordable PC based software solutions, digital SLR cameras and most recently, the development of commercially available drone (UAV) based digital camera systems. Modern digital photogrammetry solutions are now capable of very quickly capturing high resolution, high accuracy and generally high quality measurements with flexible outputs ideally suited to 3D surface modelling and measurement problems. These technical attributes in tandem with affordable digital cameras and modern UAV platforms has opened up a wide range of applications, many of which are in mining, engineering and monitoring fields.
More important than any particular measurement technology, effective survey monitoring, or any type of monitoring, starts with clearly understanding: what has to be measured (critical parameter(s)), how accurately it needs to be measured, and at what frequency are the measurements required? Only once these factors are crystal clear should we start to consider which technology or combination of measurement techniques is most suitable for the project. In many cases, an integrated approach utilizing a blend of ‘surveying’ and ‘geotechnical’ measurements will deliver the optimal monitoring strategy.
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Excavation Induced Response Of Pile Foundations
In urban areas excavations for construction of basements, tunnels and other underground facilities inevitably influence the existing pile foundations. Due to the release of stresses during excavations, confining pressures around existing piles decrease significantly inducing additional deflections and bending moments. It is important to quantify these effects at the design stage, in order to protect the existing structures during nearby deep excavations. In this paper, the impact of excavation induced ground movements on adjacent pile groups is investigated. Numerical simulations based on the finite element method are performed on free-head and capped-head piles in different pile configurations. The problem was modelled considering the three-dimensional geometry, which facilitates to simulate the arching and shielding effect of piles within a group. The response of both interior and peripheral piles is investigated. Results show that the presence of front piles reduces the detrimental effects on the rear piles within the group. In addition the provision of a pile cap significantly reduces the deflection of pile group due to load transfer to the rear piles, which are located away from the wall supporting the excavation. Outcomes of this research will contribute towards the design and construction of resilient pile foundations.
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Breaking new ground for Geotechnics in Infrastructure Delivery
Technology has had a significant impact on the information available to us in all aspects of our lives. This has allowed us to do things that were previously not possible. Both in our personal lives and in our professional lives.
In the Engineering and Construction sector, technology has allowed for new ways to design and collaborate. Working in a BIM/Digital Engineering based environment changes the way information can be shared and connected. This way of working is mature in the vertical infrastructure (buildings) space and is now also becoming standard practice on civil linear infrastructure projects.
This paper will explore how the technology has changed and what this means for the Geotechnics profession. It will outline how geotechnical engineers take advantage of the information that is being produced. Conversely, how they can utilise similar technology in the way they analyse and communicate their own technical information. It will highlight how technology will allow for improved collaboration between Design, Construction and Geotechnics.
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Managing slope instability hazards affecting local roads within the city of Wollongong
Wollongong has a spectacular setting on a narrow coastal plain between the Tasman Sea and the Illawarra Escarpment. Its temperate maritime climate in combination with this landscape periodically produces both short term intense rainfall and prolonged periods of high rainfall. A consequence of these rainfall events is that Wollongong is prone to most forms of slope instability but especially rockfalls, landslides and debris flows. Some form of slope instability has been recorded in almost every suburb of the city. The vast majority of these locations are within developed parts of the city. Their management is therefore of vital importance to all stakeholders. This paper discusses the role of Wollongong City Council in its management of slope instability as it affects its road assets.
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An Advanced Web-Based Management System for Instrumentation and Monitoring Data
EIC GeoView is an advanced web-based management system for instrumentation and monitoring data that has been developed by EIC Activities, a member of CIMIC Group, for sole use on the Group’s construction projects providing valuable competitive advantage. The System automates the processing of raw data and delivers graphical outputs of the information via an online portal. This system has the capacity to collate information from innumerable sources, then process and store the information via a cloud server. This paper presents how EIC GeoView has been used on three major projects in Australia to collate and process monitoring data to assess the performance and management of built structures. On the Torrens Road to River Torrens Project in South Australia, EIC GeoView was used to manage large quantities of movement data collected along a 3km long soil nail wall designed using unsaturated soil mechanics principles. Use of EIC GeoView allowed large volumes of data to be accurately delegated and processed with ease and minimal human effort. On Sydney Metro Northwest TSC, EIC GeoView was used to collate and process real-time rail track movements and ground surface deformation of existing structures relative to the progress of the underground tunnel, presenting the construction team with the ability to assess the impact of tunnel construction with up-to-the-minute accuracy. On the Frederickton to Eungai Pacific Highway Upgrade project, a considerable portion of the alignment involved construction upon soft soils. The grouping functionality in EIC GeoView was used to cluster different instrument readings on a single output, allowing engineers to observe and compare between linked phenomena, such as piezometer records, fill height, horizontal profile gauges and ground settlements from plate readings, all at the same time.