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Monitoring the effects of construction on nearby sensitive structures
The West Gate Freeway Upgrade involved widening and construction of new access ramps for the existing elevated freeway in a congested area of South Melbourne, underlain by the complex geology of the Yarra Delta. There were significant constraints on the locations of the bridge piers and it was often necessary to construct foundations near critical sensitive structures and services, including an old, but still heavily used brick-lined sewer. In view of the risk of damage to such services, a conservative approach to the design and construction of foundations in the vicinity is taken to minimize ground movements and vibrations, for example substituting bored piles for driven piles, but at a significant increase in time and cost. In order to speed up construction and reduce costs, Douglas Partners on behalf of the West Gate Freeway Alliance undertook trials to predict the effects of pile driving on the surrounding ground to allow the use of driven piles in areas adjacent to sensitive structures. Subsequently, monitoring was undertaken during construction to verify the predictions and included inclinometers and a recoverable below ground vibration monitoring geophone. The monitoring demonstrated that ground behaviour was within acceptable limits and subsequent surveys of some of the services confirmed no damage.
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Performance of reinforced soil wall supported by stone columns
A 10 m high reinforced soil (RS) wall has been designed to retain an access road and also the building platform for a mixed development located over a valley terrain. Within the lower part of the valley where the wall is located, the unfavourable ground conditions consisting of approximately 12 m thick soft compressible alluvial deposits overlying a stiff granitic residual formation was revealed during the subsurface investigation. In order to support the high wall vertically and laterally stone columns were adopted for ground treatment as an economic solution. This paper demonstrates the design aspects of the stone column support as a composite treatment for unfavourable ground conditions, the construction QA/QC measures and the verification of the performance using a comprehensive instrumentation scheme. From the instrumentation results the inclinometer and extensometer installed at the edge of the wall show minor lateral squeezing and settlement of the subsoil within the influence depth of the RS wall. However the deformation of the wall as a result of the lateral and settlement movements of the supporting ground is satisfactory and indicates the effectiveness and economy of this proposed solution.
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Monitoring of Mining Induced Movements Between Bridge Components with Fibre Bragg Grating Sensors
This paper outlines a novel use of Monitor Optics Systems’ (MOS) Fibre Bragg Grating (FBG) sensor cables to monitor relative movements between bridge components. Twin bridges that form part of the M1 Motorway in Helensburgh were to be subjected to ground movements caused by subsidence from planned underground Longwall coal mining parallel to the bridges. An engineering assessment was carried out to determine the risk of movements of bridge pier and abutment footings relative to the bridges’ headstocks, abutments and deck. It showed that relative movements of 5mm or more between headstocks and abutments could cause cracking in areas that cannot be visually inspected and that are difficult to repair, and relative movements of more than 16mm could lead to structural failure. A technical committee formed to manage subsidence effects on RMS infrastructure agreed that a surveying accuracy of 2mm was the minimum requirement to determine trends in movements between bridge components. As conventional relative 3D survey has a tolerance of +/- 2.5mm, it was agreed that a more accurate monitoring solution was required.
MOS initially proposed using their FBG sensor cables between bridge footings to measure relative movements, but it was deemed impractical and expensive due to the difficulties associated with installing sensor cables underground. MOS then proposed using their sensor cables held in tension between headstocks and abutments to measure relative horizontal movements. The solution would provide measurements of relative horizontal orthogonal shifts at the corner of each abutment and headstock at an accuracy of approximately 0.02mm. Sensor cables could not be installed between headstocks and the bottom of piers due to the risk of vandalism, so tilt meters were proposed to measure in-plane transverse tilts of the outer piers instead, and traditional 3D surveying for all other measurements. The technical committee concluded that the proposed solution would be adequate for their requirements.
A clamping system was developed for the sensor cables and the monitoring system was installed in 2016. The sensors are monitored at pre-determined times with demodulation equipment that is battery powered. Data is automatically sent to key personnel which is post processed by engineers to determine stresses in key bridge components.
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Rehabilitation of an uncontrolled landfill site for residential development
The project site was originally part of a wetland on the Swan Coastal Plain and subsequently utilised as a market garden. The site was then excavated for peat, and filled with over 120,000 m3 of uncontrolled landfill, predominantly building materials. In April 2004 a geotechnical investigation of the site indicated that about 50% of the landfill material was sand and about 30-40% was concrete and brick fragments. This paper presents an innovative rehabilitation methodology successfully employed at the site, which retained over 80% of the uncontrolled fill material. This was achieved through the re-use of the sand fraction and reclamation of the brick and concrete fragments to form rock fill. Subaqueous placement of rock fill material eliminated the need for dewatering, which might have impacted nearby wetlands and adjacent buildings.
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Precambrian rocks of the Darling Range
Precambrian rocks, consisting largely of granitic and gneissic rocks that have been intruded by dolerites, occur in the Darling Range in Perth’s eastern suburbs. The Darling Fault separates the deep sediments of the Perth Basin from the Precambrian Yilgarn Craton to the east. The geology and engineering properties of the major rock types are discussed and related to development in the area. Important geotechnical factors that affect development include the deep and variable weathering profile, expansive clay soils developed from the weathering of dolerite, faults and contact zones, erodibility, potentially collapsible soils and slope instability.
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The Application Of Permanent Shotcrete And Sprayed Membrane In Soft Ground Tunnels
Short and variable profile tunnels such as cross passages and Y-junction caverns in soft ground require an open faced
‘mined’ tunnelling approach. Traditionally these mined tunnel approaches relied on forward support and temporary
shotcrete with a second pass permanent concrete lining. Advances in forward support, shotcrete and membrane technology has enabled contractors to utilise shotcrete as a permanent lining element in soft ground and low cover environments that have greatly reduced overall construction duration and surface impacts. A number of smaller tunnel projects have recently been built in Australia utilising shotcrete as the permanent lining with extremely shallow cover.The paper focuses on the innovations and experiences gained in adopting this type of approach from the perspective of the tunnelling contractor.
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Annual General Meeting & Annual Dinner
Chris Boyd & Lt Col Dechlan Ellis (ret.)
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Performance of a 7.5m high post and panel wall under a 120t piling rig load
Melbourne Metro Rail Infrastructure Alliance (RIA) project is currently under construction as part of the larger Melbourne Metro Rail Tunnel Project in Melbourne. The works at the Eastern entrance to the Metro Tunnel include construction of a cut & cover tunnel and decline structure which will form the entrance to the metro tunnel when completed in 2025. Restricted site access including proximity to residential properties and operational live rail necessitated a purpose built temporary retaining structure as a working platform to support a 120 tonne piling rig for the installation of 18 m long CFA piles for the cut & cover tunnel structure. A post and panel wall comprising 900 diameter CFA piles with 310UC steel sections was considered a feasible solution for constraint site conditions. The maximum height of the wall was 7.5 m including a piling platform to support a piling rig track pressure of 345 kPa operating behind the wall. Ground conditions comprised cemented sandy soils of Brighton Group underlain by Fyansford Formation and high ground water level.
This paper discusses geotechnical characterisation of the site, design development, challenges and site constraints, monitoring of the wall during construction and performance of the retaining wall during the operation of the piling rig from a design and construction perspective.