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A Case Study On The Design Of Transition Zone For Cement Deep Mixing For A Port Reclamation Project
This paper describes a large container terminal project constructed in reclaimed land comprising deep soft clay that extends to RL-32 m chart datum. The wharf deck is a piled structure, and a 24 m wide area immediately behind it was constructed in 2008 using a Cement Deep Mixing (CDM) technique to improve the soft soil to provide stability. Post-construction settlement in this area was expected to be less than 35 mm in 20 years. However, the container yard some 30 m behind this area was only treated with prefabricated vertical drains (PVD) and surcharge, and post-construction settlement in this area was expected to be over 300 mm.
The design of the transition zone between the wharf and the container yard to limit differential settlement is described in this paper. In the transition zone, the CDM columns were progressively shortened so that the columns were only partially penetrating to give progressively larger post-construction settlement towards the container yard. The project was complicated by the fact that the surcharge design for the container yard was completed by another consultant and the work carried out by another contractor. In addition, the surface drainage within the area was bi-directional, making the design of the transition zone more challenging. To provide confidence to the client, reliability analyses were carried out to assess confidence levels for the predicted post-construction differential settlement to meet the design objectives.
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An Assessment Of Alternative Configurations For DCM Column-Supported Embankments To Prevent Excessive Deformations
T-shaped Deep Cement Mixed (DCM) columns are recently proposed as an alternative for conventional DCM columns with large area replacement ratios (ARR) over the entire depth. They alleviate the requirement of a Load Transfer Platform (LTP) used in conventional DCM column supported embankments to reduce the differential settlements and have the capacity to reduce the ARR significantly compared to conventional DCM columns. T-shaped DCM columns also improve the consolidation performance and reduce overall deformations, compared to embankments with conventional DCM columns. Therefore T-shaped columns are gaining popularity as an efficient alternative for conventional DCM columns in embankment construction. However, the performance of T-shaped DCM column-supported embankments has not been investigated in detail. Hence, in this study, the suitability of T-shaped DCM columns, geosynthetic layers and DCM column walls underneath side slopes of highway embankments in reducing deformations was investigated. The performance of different geosynthetic reinforcement configurations was compared in terms of column efficacy, consolidation performance and deformations in the ground. Although DCM column walls are generally considered as efficient in reducing lateral deformations, results show that T-shaped DCM columns are the most efficient in reducing both lateral deformations and settlements. Also, the results show that geosynthetic reinforcement is efficient only when used with conventional DCM columns with uniform cross sections but not with T-shaped DCM columns.
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A Cylindrical Model Of Pyrite Oxidation In Coastal Acidic Soils
Detailed analyses of acid soils in coastal areas of (New South Wales, NSW) indicate that (FeS2) oxidation occurs very close to narrow root channels. The root channels have been caused by extant organic activity and allow oxygen to diffuse through to pyritic layers. From the wall of the root channels in the pyritic layers, oxygen diffuses laterally into the acid soil matrix oxidizing the pyrite present. Such a simultaneous process can be modeled cylindrically. In this paper, a new cylindrical model is developed and solved using approximations to pyrite consumption kinetics. An adapted PDE2D code based on finite element methods is used to solve a linear approximation and Michaelis-Menten uptake kinetics. Pyrite oxidation produces acid in the soil matrix that is subsequently transported to the estaurine waterways, following high rainfall sessions causing a number of environmental disasters. An estimate of the new acid produced in the field is often required before remediation work is possible, and such an estimate may be determined easily using the new model. The result of pyrite oxidation based on the cylindrical approach demonstrate that the new model can accurately predict pyrite oxidation and acid production. The total acid production calculated using the new approach was found to be close to the actual field amount at the Berry site. The new results also compare well with the predictions made by the previous models developed for the Berry site.
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A review of the newly developed method used to prevent liquefaction of iron ore fines on bulk carriers
Liquefaction is a commonly occurring problem affecting solid bulk cargoes on board bulk carriers. If liquefaction of a solid bulk cargo occurs on board a bulk carrier it can result in the vessel listing or capsizing resulting in the loss of human life and industry assets. Recent incidents involving bulk carriers transporting iron ore fines have initiated research into, and implementation of, a new test method used to determine a safe moisture content at which it can be transported without being at risk of liquefying. The new test method, known as the ‘Modified Proctor/Fagerberg Test for Iron Ore Fines’, has been amended in the 2015 edition of the International Maritime Solid Bulk Cargoes Code and will be entered into force in 2017. The objective of this paper is to provide a review regarding the development of the Modified Proctor/Fagerberg Test developed by the Iron Ore Technical Working Group. The review focusses on the key findings from five publicly available reports released in 2013.
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In situ testing at the National Soft Soil Field Testing Facility, Ballina, New South Wales
The National Soft Soil Field Testing Facility (NFTF) provides a rare opportunity to characterise an Australian soft estuarine clay and to carry out monitored field tests that can be forecast or back-figured using the extensive characterisation data to improve engineering design methods. Several in situ testing campaigns have been performed to characterise the site, to advance full-flow penetrometer technology, to investigate correlations between in situ and laboratory tests and to develop engineering parameters and to assess the variability of the ground. A description of the tools and methods used in the testing campaign is provided in this paper along with a preliminary interpretation from the testing campaigns.
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Geotechnical Variability: In the Ground and Throughout a Career
This paper presents three aspects of geotechnical engineering research that have been conducted throughout the author’s career and concludes with a brief treatment of the use of physical models in teaching. The first research topic deals with quantifying the large-scale spatial variability of the Keswick Clay in Adelaide by means of undrained shear strength data acquired from several private consulting companies and government departments, incorporating a large number of site investigations. The mathematical technique of geostatistics is used, and it is observed that kriging with a spherical model, with a range of influence of 1000 m, a nugget of 1500 kPa2, and a sill of 2500 kPa2, is able to generate good estimates of the undrained shear strength of the Keswick Clay that can be used for preliminary design purposes. Secondly, the ground improvement technique of rolling dynamic compaction (RDC) is examined in the field and in the laboratory, and numerically by means of artificial neural networks (ANNs). It is observed that RDC is able to improve the ground to depths in excess of 3 m, and the use of transparent soils in the laboratory provides useful insights regarding the influence of RDC on the subsurface profile. In addition, ANNs facilitate the development of reliable models for the prediction of the level of ground improvement due to RDC. The third and final research topic presented involves ground improvement on the Moon. It is a work-in-progress, and early results are presented in this fascinating and exciting endeavour. The paper concludes with a brief treatment of the use of three different physical models used in teaching. It is observed that incorporating demonstrations involving physical models in teaching is helpful for enhancing student learning and engagement.
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Pressure selections for triaxial permeability testing
It is a common occurrence that geotechnical engineers, geologists and scientists request triaxial permeability testing from Construction Material Testing (CMT) laboratories without specifying the required pressures or detailing the application. This is generally as a result of a lack of understanding of the test procedures and how the pressure selection during the various stages affect the overall test result reported. Some specifiers may also nominate pressures which provide a result which potentially indicates a soil compliance under those test conditions, yet if it were tested under conditions reflective of the engineering application, would in fact fail the required specification. There are three stages of the test which require different pressure selections;
- Saturation pressures based on soil type and plasticity;
- Consolidation pressures to set the specimen equivalent to the insitu condition;
- Running the test at the desired confining stress or the mean effective stress using pressures relevant to the soil type.
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Impact from the construction of a working platform and girder lifting operations on pile/column displacements
To facilitate the initial construction of the bridge pier piles on the bank of Nambucca River in NSW Australia, a working platform was constructed over 25 m thick soft alluvial deposits. Subsequent to the pile installation and the construction of columns and headstock, it was determined that the platform needed to be raised by 1.5 m in order to allow for adequate clearance between the boom and the headstock. The raising of the working platform generated sub-soil flow that caused the piles to displace horizontally of up to 50 mm towards the river. Further, the erection of each 160 tonne girder was carried out by a super-lift operation at the raised platform. This exerted enormous bearing pressure on the platform. Surveying indicated that during the first two girder lifts, the tops of the bridge columns had displaced a further 39 mm towards the river, then recovered by about 15 mm after the lifting operation. To mitigate potential further lateral displacement for the remaining two girder lifts, a 5 m wide berm was constructed on the riverside of the pier. Surveying indicated that the placement of this counterweight had effectively limited further movement of the columns to less than 10 mm. One of the concerns with the lateral displacement of the pier was that the bending moment induced in the piles may exceed the moment capacity. Numerical analysis was carried out to back-analyse the measured lateral displacement and to assess the likely future performance of the piles.
This paper focuses on the geotechnical design of the working platform and the predictions of the lateral displacements of the pier piles, with or without the counter weights at the riverside of the pier. The comparison of the predictions and measurements, as well as the permanent effects on the pier piles are also outlined.
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A New Calculation Approach To Design Flexible Facing System For Soil Nailing
According to the experience of several researchers, under certain conditions the soil nailing facing system can be developed with nails in cooperation with steel mesh (i.e. flexible structural facing). The goal of this system is to improve the slope face stability and allow the vegetation to grow. A simple design approach was introduced a few years ago that analysed the behaviour of the mesh by comparing the maximum volume of debris that can move among the nails to the maximum volume that can be held by the mesh. Even if it took into account the real interaction between mesh and soil, such procedure was quite rudimental by solving the non-linearity of the load-displacement problem. Recently, a new design approach using forces generated by the soil pushing on the mesh was proposed considering the most unfavourable case between the two wedge analysis and the single wedge, one for slope failure mode (according to the standard BS 1006 – 2010). Concerning the mesh resistance, the new approach overcomes the non-linearity of the problem and allows a more realistic calculation approach. This has been feasible thanks to the interpretation of the load-displacement curves generated in accordance to the UNI 11437 (2012) Standard as well as to the introduction of the “scale effect” that modifies the nail spacing and mesh behaviour accordingly.
For sure the methodology is not perfect, but at least it allows appreciating the Ultimate Limit State and the Serviceability Limit State with a simple calculation. This paper analyses the main calculation steps and concepts of this new approach implemented in the new Bios 2 software which is used by Maccaferri for the design of flexible facing of cut and natural slopes.