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Earthquake-induced displacements of earth dams and embankments
This paper presents an overview of some of the available methods to estimate earth dam displacements due to earthquakes, from the simple Newmark one-dimensional displacement method to a complex coupled effective stress dynamic analysis. It discusses the assumptions used, advantages and limitations of each method. The use of pseudo-static analysis for assessing seismic stability of earth structures is critically reviewed. An example on the use of total stress dynamic analysis in the seismic upgrade work of Yarrawonga Weir in Victoria is presented. The dynamic analyses were very useful in providing an indication of possible flow failure, crack development during earthquake shaking and the potential for loss of freeboard of the earth dam. The method was also very useful to assess the most efficient remedial method that satisfies all the imposed requirements from the community and the client.
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Case Study: Mine void investigation and remediation for the West Charlestown Bypass, Newcastle
The completed West Charlestown Bypass project comprises a 6.5 km length of dual carriageway urban freeway south west of the Newcastle CBD, in New South Wales, Australia. This section of State Highway 23 extends from the Pacific Highway at Windale in the south, to Charlestown Road at Kotara in the north. A 1 km length of the Bypass, at the northern extent of the works, traverses old underground mine workings with overburden depths as shallow as 5 m ranging up to 30 m. The mine workings are within the Australasian Coal Seam and they were undertaken by two collieries, initially in the 1800’s by the Australasian Coal Company and later in the early 1900’s by the Newcastle Myall Colliery. The presence of these old mine workings and associated subsidence effects posed a difficult problem for the design and construction of the Bypass.
The Bypass design was required to be safe and serviceable, considering the potential impact of ongoing mine subsidence associated with these workings. A number of treatment options were considered, with the adopted design including a combination of excavate, collapse and backfill of shallow mine workings, and grouting of voids where the workings were located at greater depths. This paper presents a case study of the pre-construction investigations, including discussion of the methodologies adopted and their success, the design requirements and options considered, and the completed mine void treatment works.
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Direct Validation of Design Parameters of Near-Surface Materials during Construction Phase
This overview paper discusses a number of innovative insitu test techniques that could potentially be incorporated into Quality Assurance / Quality Control (QA / QC) for the assessment of near-surface materials during the construction phase of earthworks projects. The limitations of traditional QA test regimes (density-based assessments) and other tests frequently adopted for field assessment during the construction phase of projects (CBR and DCP) are initially discussed, with a critique of the continued use of index tests for such material evaluations provided. A number of alternative test techniques that are capable of rapid, direct insitu measurement of stiffness and strength parameters is made, presenting the Light Falling Weight Deflectometer (LWD), Borehole Shear Test (BST) and Variable Energy Dynamic Cone Penetrometer (PANDA Probe) as viable alternative assessment methods. The insitu parameters provided by these alternative tests can be used to directly evaluate if design parameters are being met onsite and, based on the authors extensive experience using each tool within recent major Australian construction projects, the advantages of using such innovative tools and developing project-specific thresholds for adoption of these tools within a QA / QC test regime, are discussed. Current limitations preventing the widespread implementation of these alternative test techniques are also identified.
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High tension load transfer using bored piles for SOUL Apartments, Surfers Paradise
This paper describes two different methodologies of transferring high tension loads through large diameter bored piles into the ground. The installation of post tensioned stress bars into the piles was considered as one option for the SOUL project however the use of high strength concrete (fc` ≥ 85 MPa) for the pile shaft had some essential advantages.
The use of high strength concrete for bored piles has hitherto been considered to be problematic. Workability criteria have to be maintained for several hours in order to achieve the required quality. Possible concrete shrinkage of the pile shaft causing cracks, concrete bleeding as well as an ongoing quality control of the concrete mix are only a few of the challenges that have to be considered.
This is particularly the case for the foundation piles of a high rise building where extremely high point loads are transferred through the piles into the ground. All piles have to be constructed to extremely high standards. In most cases geometry constraints and the design requirements of the superstructure make it impractical to install additional piles in the event that a pile does not achieve the required capacity and has to be supported or replaced by an adjacent pile.
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Ground characterisation and performance of a sinking motorway, waterview connection project, New Zealand
The paper presents the results and interpretations of an extensive data collected during the procurement phase of SH16 motorway upgrade. The strength and consolidation characteristics are investigated for two prevalent soil units (AH and ATcl). The AH soil is identified to manifest a response which is typical of a sensitive structured soft soil, whereas the ATcl soil is noticed to manifest an over-consolidated behaviour. The estimates based on either CSSM and SHANSEP have limitations to predict undrained shear strength profiles for the sensitive AH soil, but predicting rather well the shear strength of ATcl soil. The undrained shear ratio su/’v at OCR = 1 for AH soil appears to be a consistent indicator of shear strength development with depth. The non-linear one-dimensional compression displayed by the AH soil is proposed to model using a unique relationship between liquidity index and vertical effective stress. The predictive capability of this relationship is demonstrated by numerical simulations of settlement monitored during the construction and post-construction phase of the original SH16 motorway embankment.
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Assessment Of The Coefficient Of Consolidation With Queensland Data
Established relationships between the coefficient of consolidation (cv) and index tests are used during both preliminary design and as a cross check during detailed design. The laboratory oedometer test provides compressibility parameters and a lower bound of cv, while the coefficients of consolidation are preferred from the field dissipation tests. However, cv is dependent on the method used to determine its value, stress level, and over-consolidation ratio. In practice, the coefficient of consolidation values obtained from dissipation tests are used to predict settlement time, while oedometer tests are useful in obtaining the parameter required to predict the magnitude of settlement. However, dissipation tests measure the horizontal coefficient of consolidation (ch) which needs to be related back to the vertical value. These standard approaches are discussed using test data from Queensland sites. Inconsistencies in correlations are used to show that design should consider the wide variability in interpretations that can occur, and correlations of cv with index tests should not be used in detailed design. Additionally, the cv values obtained from oedometer testing is a poor predictor of time for consolidation. This could also be due to the size of samples being not large enough for the soil structure. Monitoring data from construction sites are used to assess a “moderately” conservative design value from dissipation and lab tests.
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Geotechnical characteristics of coal mine spoil
This paper presents data on the geotechnical characteristics of the overburden, or spoil, produced during open-cut mining operations in the Hunter Valley, specifically in relation to the stability of spoil piles and the hydraulic characteristics of spoil and post-mining landscapes. A value of 33.4° is reported for the peak shear strength of “typical” spoil. This value is shown to reduce slightly at large shear strains and further when spoil materials are sheared after breaking down on exposure to water. Data on the permeability of different spoil types is presented, showing that permeability decreases with mudrock content. The presence of coal in the spoil is shown to have a significant effect on its hydraulic properties. Due to its hydrophobic tendencies, coal tends to resist the infiltration of water. However, spoils containing coal also tend to resist the storage of water that does infiltrate, causing coal-rich materials to drain quickly. This is demonstrated by considering the water retention properties of washed coal. The spoils are shown to have significant quantities of total leachable salt, but that leaching by a significant volume of water is needed for its total removal. The results show that a significant amount of salt is released upon first leaching, but that the rate of leaching decreases significantly with continued rainfall percolation. The paper concludes with a brief discussion of the potential for salt leaching from mine-spoil landscapes and its consequences for water quality in post-mining environments.
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Geotechnical History And Rehabilitation of the Rhyndaston Rail Tunnel, Tasmania
Rhyndaston Tunnel is located 40 km (73 km by rail) north of Hobart in southern Tasmania. It was the first and remains the longest rail tunnel excavated in Tasmania and in 2021 was the only one still in operation. It was excavated by traditional drill and blast in sandstone between 1873-1876. The 955 m tunnel was recognised as having a small, if not limiting, profile soon after operations began. The advent of containerised freight in the late 1950’s and its rapid adoption across the globe in the 1960’s meant that the tunnel would soon become redundant and a viable and cost-effective alternative was sought.
At about the same time, the Hydro Electric Commission of Tasmania chose emerging tunnel boring technology for the excavation of the Headrace and Tailrace Tunnels for the Poatina Power Station 80 km to the northwest. This was to be the first use of tunnel boring technology in Australia, and it also provided a practical option to enlarge the Rhyndaston Tunnel while maintaining the majority of services on the Main Line between Hobart and Launceston. Consequently, after the completion of tunnel boring activities at Poatina in 1963, the tunnel boring machine (TBM) was transported to Rhyndaston and reamed the Rhyndaston Tunnel in 1964-1965.
The original Rhyndaston Tunnel was largely unlined and unsupported and when, after almost ninety years of operation, it was enlarged, it remained largely unlined and unsupported. A further 50 years on, and an extreme rainfall and extensive flooding across Tasmania saw the Rhyndaston Tunnel on the list of the States many civil assets to sustain damage. The extent of that damage was small, but in the course of remediation, the opportunity was taken to repair and upgrade a number of identified defects with a view to ensuring the Tunnel’s long-term security.
The paper describes the geotechnical history, enlargement and recent remediation and upgrading of the Rhyndaston Tunnel. All photographs are from the period 2016 – 2020 unless stated otherwise.
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Deep Dry Soil Mixing – Performance And Quality Control Acceptance Criteria
The variability in strength and compressibility of in situ deep soil mixing (DSM) of soft soils can be greater than the variability of the natural soil. To achieve economy, sustainability and performance of DSM, it is essential that construction be carried out using an appropriate QA/QC program.
This paper presents the results on the use of DSM columns to support several embankments over soft clay in the Ballina Bypass and Pimlico to Teven Pacific Highway projects. The DSM work was carried out under the Roads and Maritime Services (RMS) Specification, with QA/QC testing procedures developed specifically for these projects. Embankments with contrasting performance are compared to the quality control test results which comprised laboratory testing of core samples as well as in situ test results such as pull-out and push-in vanes and conventional cone penetration tests. Settlement monitoring indicated that where the acceptance criteria are met measured settlements under embankment loading were generally less than predicted settlements. The observed settlement in an area with high organic content was twice the predicted value, although in all cases, post-construction settlement met the performance objectives.
Based on these results, recommendations on QA/QC testing procedures are made with the aim of improving economical and sustainable construction of the DSM ground improvement technique for soft soils.