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Standpipe Piezometer Installations β Lessons Learnt
Standpipe piezometer installations are frequently commissioned as part of site investigations to monitor groundwater levels and chemistry. On a recent site investigation for a large tunnel infrastructure project in Sydney, Australia, 15 standpipe piezometers were installed and developed. Some of the well screen depths exceeded 100 m below ground surface. Several of these wells, especially the deeper ones, returned unexpectedly high pH values after development and sampling. The values were potentially misleading for the assessment of infrastructure durability and environmental impacts.
A hypothesis for these high pH readings was the potential ingress of the cement-bentonite grout in the annulus to the standpipe piezometer via the bentonite seal and/or the casing threads. The latter was confirmed by borehole imaging. Following this observation, a literature review and trials were carried out to investigate the impacts of typical well construction methodology and materials on the pH of the groundwater sampled. In particular, threads from several PN18 nominal pressure rated casing were tested, with their elastomeric joints, at different confining pressures. The effectiveness of the bentonite seal above the screened section was also tested by varying curing time and seal thickness for different overburden pressures. This paper discusses the results of these trials and describes measures to reduce the risk of groundwater contamination induced by cement-bentonite grout leakage.
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Road Tunnels In Australia And New Zealand β Getting The Best Value For Money
A brief comparison of the cost of recent road tunnels will be presented to bring focus on the various procurement models that have been used in recent years to deliver road tunnels in Australia and New Zealand. The delivery mechanisms have included Public, Private, Partnerships (PPPs) for the provisions of road infrastructure involving concession holders and design and construct contracts and alliances between builders and government agencies. Most of the PPP tunnel projects went into receivership soon after opening, demonstrating that the cost of tunnel construction vastly exceeded the investment value as serviced by toll income. These projects will be compared with the Waterview Connection road tunnel in Auckland which was undertaken under a competitive alliance model under government finance to complete a missing link on a non-tolled motorway. Comments will be provided on the consequences on design /construction and operations and maintenance arising from the different procurement models based on the authors experience to deliver such projects as undertaken on Lane Cove, CLEM7, Airport Link Brisbane, the cancelled East West tunnel in Melbourne and Waterview Connection in New Zealand. The role of site investigation, geotechnical base line reports, the amount of detail in reference design and scope of works and technical criteria will be commented upon. Other tunnels under construction and potential forthcoming projects and their completion dates will be reviewed to outline the current tunnel construction pipeline.
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Urban salinity scoping study for Greater Launceston area: Part 1 Hydrogeological setting
Before developing salinity hazard maps or proposing management actions, it is crucial to obtain an understanding of the processes governing groundwater movement and salinity at an appropriate scale. Fundamental to understanding groundwater movement is the origin, deposition, weathering and fracture characteristics of the soil and rock that constitute the regolith. This paper describes the process involved in establishing the hydrogeological setting for an urban salinity scoping study carried out on a pilot study area in Launceston. The major factors involved in a typical hydrologic cycle are considered at the level of a desk top study of existing information, including topography, climate, land use and land use changes, surface water, geology, salt sources and salt stores, and possible groundwater flow systems. The end product is a conceptual groundwater model that can be validated by field investigations and measurements.
The companion paper describes the results of an investigation including drilling and laboratory testing.
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South Australian collapsing soils
The study was designed to evaluate and compare typical collapsing soils from South Australia and to evaluate the use of such soil in pavement construction after chemical stabilization with cement and rice husk ash (RHA). The three soils in the study were classified as silty sands, usually with calcium carbonate. Shear strength decreased markedly with inundation. In the natural state, a severe degree of collapse could be reached following saturation. The stabilization of soil from Port Augusta resulted in reduction of the collapse index and an increase of the shear strength. Even after heavy compaction, the soil still had slight potential for collapse upon wetting. On the other hand, the chemically stabilized and compacted soil exhibited minor swelling upon wetting. The saturated shear strength of compacted soil increased when compared to that of undisturbed soil. For evaluation of application of the stabilized soil in pavement construction, the California Bearing Ratio (CBR), unconfined compressive strength and durability were determined. Based on the soaked CBR and strength tests, the non-stabilized, compacted soil was classified as a good sub-grade. The chemically stabilized soil with a low percentage of additives could be used as a sub-base. However durability testing indicated stabilization with either 6% cement and 2% RHA is required. Further work is required to determine the resilient properties of compacted stabilized collapsing soil.
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Soft Soil Engineering In Practice
Engineering development on soft soils has grown rapidly in recent years, spurred by an increasing demand on land space for infrastructure expansion. However, the combination of poor strength, high compressibility and low permeability characteristics inherent to soft soils form a problematic suite of conditions, placing overlying structures at risk of excessive deformation and instability. Managing these conditions is particularly challenging to designers and constructors. This paper presents a summary of the critical findings and conclusions gained through the authorβs own experience in designing embankments over soft soils. Particular emphasis is placed on the interpretation of geotechnical parameters using empirical correlations to validate test results and design assumptions, and specific design considerations that may impact on the performance of embankments built on soft soils. This paper also discusses design criteria, methods for settlement and stability control, commonly used ground stabilisation techniques, and approach to manage soft soil risks. The purpose of the paper is to provide suggestions towards a holistic approach to soft soil engineering based on the authorβs experience. Examples are also provided to illustrate the authorβs views and findings, which are not intended to be exhaustive.
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Professional tasks, responsibilities and co-operation in ground engineering
In July 2002, a Joint European Working Group on the professional competencies of engineering geologists and geotechnical engineers was formally established by the then Presidents of the ISRM (Panet) and ISSMGE (van Impe) and by the President designate of the IAEG (Rengers). IAEG, ISRM and ISSMGE are learned societies in the broader field of ground engineering.
The need for such a Working Group stemmed from the fact that in recent years and across several European countries there was a debate on the particular contribution and responsibilities of Engineering Geologists and Geotechnical Engineers in the solution of problems in ground engineering. This was emphasised by differing professional definitions and accreditation rules that existed for geologists and engineers within different European countries, and by the growing demand for geologically and technically sustainable, cost effective and safe geo-engineering solutions. Internally, the Joint Working Group was seen as a means of strengthening the co-operation across the three international societies and to identify common ground.
The members of the Joint Working Group were nominated by each of the three international societies involved. The European Federation of Geologists (EFG) is represented on the Working Group as observer at present.
The Working Group was established on the 20-21 March, 2003 in Brussels. The inaugural meeting agreed the Terms of Reference. It identified the need for two documents, namely:
- A document for the three international learned societies on the professional competencies of engineering geologists
and geotechnical engineers, including a specification of the interfaces and areas of co-operation between them and - A document with relevant recommendations for an input to EU Directives.
This Report represents the outcome of the Working Groupβs deliberations on the professional competencies of Engineering Geologists and Geotechnical Engineers within civil or structural engineering. For the purposes of this Report, Geotechnical Engineers are Soil or Rock Mechanics practitioners. After approval by the three international societies involved, this Report will be the basis for the second document of the Working Group to be prepared for the appropriate EU Authorities. It is intended to have representatives of both EFG and FEANI involved as full members of the Working Group in the preparation of the second document.
- A document for the three international learned societies on the professional competencies of engineering geologists
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Alliance Enhances Geotechnical Outcomes Port Of Brisbane Seawall
One of the largest infrastructure projects handled by Port of Brisbane Pty Ltd (formerly Port of Brisbane Corporation) in the last two decades is the construction of a 4.6km long seawall extending 1.8km into Moreton Bay. The perimeter seawall constructed encloses an area of 230 hectares immediately north-east of the current Port area. The area contained by the wall is being reclaimed in a progressive manner and currently 40% has been fully reclaimed and a further 20% partially reclaimed.
The Future Port Expansion (FPE) seawall was designed and constructed by an Alliance comprising Coffey Geosciences (Geotechnical Consultant), Leighton Contractors (Contractor), Parsons Brinckerhoff Australia (Civil Consultant) and WBM Oceanics (Hydraulic Consultant) along with the Client, Port of Brisbane Corporation (PBC), a semi-government organisation. After studying several delivery methods, the Alliance delivery method was adopted by PBC to best meet the potential risks associated with the construction of the seawall on a site underlain by more than 30m of deep soft compressible soils and concerns over impacts of construction on the sensitive environment of the adjacent Moreton Bay Marine Park which surrounds the site. The complexity associated with the project also involved the variable water depth to the seabed, significant tidal variations over 24 hours, weather conditions, timelines and turbidity issues related to construction. From Day 1, the Alliance committed to risk management related to geotechnical and environmental issues which led to several innovative solutions and outcomes. The positive outcomes achieved could be directly related to the collaboration between a semi-government organisation, a major contractor and several consultants through the Alliance delivery mechanism which helped to streamline the design and construction work and removed the inflexibility usually associated with other contracted forms of project delivery.
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AGS Victoria Symposium 2023
Novel Solutions in Geotechnical Engineering
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Comparison Of Different Hard Rock Drilling Methods For Bored Piles
Drilling penetration into rock becomes more difficult with increasing hole diameters and rock compressive strength. In piling applications, hard rock formations have to be cut and excavated prior to the installation of the foundation piles and/or piled retaining walls. Commonly, conventional rotary drill tools are used for bored piles in medium to very high strength rocks. For harder rock formations different methods have to be adopted as much larger cutting energy and force input are normally required to break the material at the rock tool interface.
Cluster drilling is a proven method to penetrate rocks with strengths exceeding 100 MPa. The method has been used successfully for decades in America, Asia and Europe for applications in the mining and construction industry with diameters usually ranging from 600 to 2400 mm. In Australia cluster drilling has recently been used for mining and modest construction applications. However, in 2010 Piling Contractors Pty Ltd has started utilizing innovatively designed and built cluster drills for the penetration of extremely high strength rock formations. Since then, more than 1,000 linear meters of extremely high strength rock (most of it with UCS in excess of 200 MPa) was successfully excavated using this technology for the installation of bored piles.
Air roller core barrels were also utilized in the past for various projects involving hard rock drilling. Basic working principles and limitations of these two traditional techniques compared to cluster drilling are identified and discussed in this paper.
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Fibre Reinforced Soils For Geotechnical Infrastructure
This paper presents the results of recent laboratory studies on fibre reinforced soils. Drained and undrained triaxial test results highlight how soil stress-strain behaviour may be altered by mixing with discrete flexible fibres. In triaxial compression a considerable strength increase is induced by the presence of fibres, while in extension the strength increase is very limited. This is attributed to the fibre orientation distribution with respect to the tensile strains developed. Also presented in the paper is a framework for introducing the effects of fibres and their orientation into a constitutive model to describe the anisotropic stress-strain behaviour of fibre reinforced soils. Model simulations of selected test results are shown. Also described are examples of future investigations and trials required to make the soil reinforcement technology ready for use in industry.