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The application of jet grouting for the construction of Sydney International Airport runway end safety area
The Runway End Safety Area (RESA) is part of the upgrade plan of the Sydney International Airport and adds an extension to the end of the runway. As this area passes through a number of existing facilities it will have to be bridged over a heritage listed sewer, an airport perimeter road and the existing highway road.
The area of RESA was previously low lying farming land with major alterations in the ground contours due to previous construction works. The site is on man-made filling up to 4 m thick from earlier dredging works and predominantly marine originated alluvium. Soft mud deposits are extensively spread over the area and groundwater level is quite shallow.
The loads introduced by bridging RESA over existing structures and lowering the road level at the intersection with RESA required specific geotechnical measures.
Jet Grouting has been used successfully in RESA with multiple purposes such as increasing the ground’s bearing, retaining the ground and creating impermeable barriers to cut off the flow of water during construction. Multiple requirements and variations in ground conditions required a detailed design with a number of Jet Grout column diameters, lengths and combinations. Design included finite element analyses using Plaxis and later verified by sampling of grout and installing inclinometers to measure ground deformations.
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An Alternative Approach To Assessing Post Construction Settlement With Incomplete Preload Settlement Data
Soft clays are commonly encountered in construction projects undertaken in coastal alluvial environments and can undergo large settlements when subjected to vertical stresses larger than previously experienced. Building on soft clay sites typically requires geotechnical assessment and treatments to manage the risk associated with excessive total and differential settlement resulting from primary consolidation and creep mechanisms. Preloading or surcharging of soft clays is a common treatment used to induce the majority of primary consolidation settlement prior to construction, and to reduce the magnitude and variability in long-term settlement post-construction. Review of monitoring data captured within the preload or surcharge period is normally necessary to assist in the prediction of post-construction settlement over the design life of the development. The monitoring data is typically used to identify when the surcharge can be removed, allowing a prediction of the long-term settlement based on key parameters including the achieved over- consolidation ratio (OCR). This paper presents an alternate approach to assessing post-construction settlement when settlement monitoring data is unavailable or incomplete. The method relies on in-situ Cone Penetration Test (CPTu) data to estimate the pre-consolidation pressure of the soft clay deposit under the surcharge load and a calculation to consider the resulting OCR after surcharge removal. The resulting values of OCR are used to assess reduced creep settlement rates based on published information to predict the post-construction settlement. The method is demonstrated with data from a site in south-east Queensland.
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Field and laboratory investigation of an expansive soil site in Melbourne
Expansive soils undergo heave and settlement due to soil moisture changes, causing differential movement to light weight structures built on them. These movements may be significant when extreme weather conditions such as prolonged droughts are encountered. Indeed, there have been major concerns regarding footing movements and cracks in houses in Victoria following the breaking of the last prolonged drought experienced in the late 90s to early 2000s.
As part of an ongoing research project at Swinburne University of Technology on damage to residential structures due to ground movements, a field site was established in a western suburb of Melbourne. In situ soil moisture variation and corresponding ground movements are monitored using a neutron moisture probe and magnetic extensometers respectively. In addition, various laboratory experiments including soil classification, suction, swell and shrinkage were carried out on both disturbed and undisturbed soil samples collected from the field site. Suction variations of undisturbed soil along with moisture content have been measured using miniature tensiometers and a Chilled Mirror Hygrometer to develop the Soil Water Characteristic Curve (SWCC). Atterberg limit tests and particle size distribution tests have also been carried out at different depths to classify the soil.
This paper discusses results from both the field and the laboratory investigations. In addition, it presents mechanical and hydraulic properties of the field soil that can be used in numerical analyses.
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AGS NSW Research Award 2020
Davide Guccione, Aruni Abeywickrama, Navid Yeganeh and Ye Aung
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Appropriate Intrusive Site Investigations Save Our Clients’ Money
This paper demonstrates how a supplementary, targeted ground investigation has the potential to considerably reduce construction cost, program and ground related risks. A case study is presented based on the draft final earthworks design of a proposed metro trains stabling facility which was first conducted based on limited site investigation (SI) data and then revised based on a targeted ground investigation. The earthworks design required site levels of a low-lying brownfield site to be raised by up to 3m. The site is underlain by significant depths of superficial deposits and long-term consolidation settlements pose an operational risk. The limited extent of the initial SI led to a large uncertainty in key design parameters and settlement predictions exceeded operational tolerances. This raised the requirement for potentially prolonged and expensive ground improvement works. A targeted SI was designed to reduce parameter uncertainty and the subsequent analysis reduced the settlement estimate magnitude and uncertainty negating the need for ground improvement works.
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Numerical modelling of soil-infilled rock discontinuities
Numerical modelling often form an essential part in the design of urban tunnels in order to evaluate the interaction of the geo-structure with other structures in the vicinity of the excavation (buildings, public services, driveways etc.), the design of the support and to establish limits of alert during the construction. With the understanding that rock joints play a key role in a rock mass, the approach used for such prediction should be able to describe all important mechanisms characterising a discontinuous medium. In this scenario, rock joints that are filled with fine materials are likely to be the weakest elements in a rock mass, having a dominant influence on its overall shear behaviour because of the low frictional properties of the infill. This paper presents a discussion on some of the relevant factors affecting the shear behaviour of soil-infilled rock discontinuities. To illustrate the effect of some of those factors in a class A prediction, a hypothetical example of a cavern excavation in a jointed medium is presented. The analysis is based on a discontinuum approach and performed using the distinct element program UDEC. A new semi-empirical yield criterion for soil-infilled rock discontinuities under constant normal stiffness conditions has been employed and compared to the conventional Mohr-Coulomb slip model. The new criterion better describes the shear behaviour of the rock joint resulting in a difference of approximately 50% in the induced settlement at the surface.
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Shaft design for large-diameter microtunnelling in soft ground
This paper examines parametric studies in the geometrical dimensioning, configuration and spatial efficiencies of large diameter shafts. Structural design aspects, construction solutions for excavation stability and parametric studies on ground improvement for deep shafts are also discussed.
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Applying the Engineering Geological Model Approach to Quaternary Glacial Geology in Western Tasmania
Tasmania is unique in Australia for its extensive, preserved glacial landscapes, which are concentrated in remote areas. Numerous high-value mining and hydroelectric assets in those settings necessitate understanding of glacial features, including their geomorphological indicators, stratigraphical complexity, and geomechanical conditions. At least five Quaternary glaciations of progressively more limited extent have been differentiated in Tasmania. They span from at least the Early Pleistocene (ca. 1 Ma) to the Last Glacial Maximum (ca. 20-18 ka) with all glaciers having disappeared by 14 ka. Glacial deposits can be geotechnically challenging due to high heterogeneity and anisotropy, producing complex lateral and vertical variations in geomechanical properties. The wide age range of Tasmania’s glacial deposits contributes further complexity through variations in weathering and cementation. The Engineering Geological Model (EGM) approach helps firstly to effectively identify and assess geological relationships and geotechnical properties, and secondly to adequately address these conditions during engineering design and construction. In previously glaciated landscapes, this approach provides an important framework to enable thorough understanding of complex deposits, consequent geomechanical behaviour, and potential hazards. This paper outlines the geotechnical investigation methodologies that are potentially suitable for diverse glacial units and demonstrates the utility of the EGM approach through its application to a new tailings storage facility at Renison Bell in western Tasmania. There, three glacial units were encountered: surficial, glaciofluvial sandy gravel of variable thickness and permeability; weak, liquefiable, rhythmically laminated glaciolacustrine silt and clay; and previously unidentified, locally indurated till draping bedrock. Their properties, stratigraphical relationships, and geographical distributions suggest that these units record the first two glaciations to affect Pieman Valley. A desktop study and conceptual model, substantially refined as an observational model, provided interpretation confidence and enabled completion of construction on time.
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Managing a ground stability hazard in a residential area
Landsliding was discovered to be the cause of longstanding periodic disruption to roads and services in a coastal residential area on the Coromandel Peninsula of New Zealand’s North Island. Investigations and monitoring of the landslide complex, which covers about 50 hectares in area, commenced in 1996 and continued through to 2011. The investigations showed both inactive and slow moving landslides in volcanic geology, and movement is maintained by high groundwater pressures and the slow removal of toe material by coastal erosion. The landslides are ancient and include shallow and deep seated components. Stabilising the main landslide feature is deemed not to be feasible due to the depth of the slide plane, and a method of assessing and managing risk to properties was developed in conjunction with landowners and the local council. The geology, ground and groundwater conditions, triggers for landslide movement, landslide effects on infrastructure, movement monitoring and risk management strategy adopted are described.
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A large diameter ring shear apparatus and the effects of long distance shearing on interface friction angles and grain crushing
A large diameter ring shear has been constructed at the University of Sydney. A brief description of the apparatus is presented in this paper. The ring shear is particularly suited for large displacement shearing of sand against an interface. Some data is presented from tests shearing silica and calcareous sands against rough and smooth steel interfaces to show the effect that large displacement shearing can have on the interface friction angle and grain crushing.