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Analysis of soil-foundation-structure interaction to load transfer mechanism in reinforced piled embankments
The scope of this paper is the analysis of a piled embankment reinforced geosynthetic with discrete element method and soil model at the microscopic level. The vertical stress distribution, load transfer mechanism, efficacy, differential settlement and tension in geosynthetic were chosen for comparison and interpretation of results. The contribution of tensioned membrane effect by geosynthetic reinforcement to load transfer mechanism is elucidated through the numerical analysis, which is generally neglected in the most current design procedures. Additionally, a new analytical approach was proposed to analyze the load-deflection behavior. This method is the results of the combination of the tensioned membrane theory and soil arching theory, thereby providing a more suitable design approach and believed to be a useful tool for engineers in designing the soil-geosynthetic system. The validity of the analytical method is compared to the numerical results by using the discrete element method. Thus, the results of this study are intended to provide some guidelines for designers and to bring insight about the interacting mechanisms into the design process.
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The interplay of site reactivity, design practice and construction procurement in structural failures on expansive clay sites
The expansion of housing into the Western suburbs of Melbourne has involved, effectively, mass-production of conventional, masonry veneer dwellings on highly reactive sites. The design favoured by constructors for reasons of cost and speed is the “waffle pod” system, typically 385mm deep on highly reactive sites, with the performance of such footings generally predicated on adequate control of soil moisture in the foundations close to the footprint of the building, both during construction and in the permanent condition.
Damage to masonry facades and excessive floor slab deformations, evidently due to serviceability failure of footing systems, have led to recent publicity and litigation. Whilst the underlying geotechnical characteristics may be causative of soil heave, the unique characteristics of waffle pod footing systems and the associated landscaping and drainage provisions stipulated by the designers, along with the method of procurement of the house itself point to the contribution of systemic and contractual factors in footing failures.
A further aspect is the interplay of differing deformation criteria between AS2870 (“the Standard”) and the structural design standards such as AS1684, whereby, again, dissociated procurement and design of building components (footings and roof trusses in this instance) can lead to incompatibilities in structural behaviour and consequent damage to cladding and finishes. This paper examines the interplay of geotechnical, structural, construction detailing and contractual aspects that can lead down the path to poor footing performance, dispute, and litigation. The question is raised as to whether, given these relatively gross uncertainties relating to the input parameters for codified standard designs and design methods, the degree of refinement and accuracy implicit in the Standard is warranted, and whether more robust standardised designs are justified.
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The use of early-works embankments in soft soil areas to optimise detailed design: Gateway motorway case study
This paper presents a case study on the use of early-works preload embankments in soft soils areas to provide information to optimise detailed design. The Gateway Upgrade North (GUN) project involved the widening of the existing Gateway motorway from four to six lanes with some areas of re-alignment. Early-works for the motorway upgrade involved construction of sections of embankment located in areas of soft soils. From a geotechnical perspective, the early-works were essentially instrumented trial embankments constructed 9 to 12 months ahead of the main package and therefore provided an opportunity to observe embankment and wick drain performance and back-analyse soft soil consolidation parameters used for the detailed design for the final motorway construction.
Data from settlement plates, vibrating wire piezometers and inclinometers was used in conjunction with site investigation and laboratory data to assess consolidation parameters of highly compressible Holocene-age alluvial clays. Asaoka’s method and Terzaghi’s theory of one-dimensional consolidation were used in the back analysis of primary consolidation parameters. Secondary settlement was also observed allowing back analysis of secondary compression parameters. Using consolidation parameters derived from the back analysis, design parameters were allocated to relevant geological units which were then applied in settlement modelling for critical sections in the detailed design.
Assessment of the early-works embankment monitoring data enabled a more robust prediction of embankment behaviour during and post-construction. This resulted in a more cost-effective and optimised embankment design with higher confidence in predicted post-construction settlements.
The term preloading is used in this paper to refer to both ‘preloading’ and ‘surcharging’. The former is the application of a temporary load, usually via fill, equivalent to the future fill plus in-service load, for inducing a substantial fraction of the expected settlement prior to construction. The latter refers to applying extra load to enhance preloading.
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Practice Note No. 8
This Practice Note must be read in conjunction with the other Practice Notes from FFSV.
The following is a discussion on the methodology to be used by FFSV members when undertaking the investigation and reporting of movement and distress in lightly loaded structures. The methods and procedures relating to the investigation and reporting of distress in lightly loaded structures are not limited to this Practice Note.
A distressed building investigation report must provide a sufficient evidentiary base in order to establish a reliable professional opinion. While such reports are commonly used in insurance claims and legal cases, to help determine liability, it is critical that the reports themselves remain completely objective and independent. Damages awarded in building disputes can be very substantial, therefore objective independence is the key component in these reports. Such impartiality will help ensure a better understanding of the relevant issues by all parties. In the preparation of an expert technical report, there is no obligation to make findings that are favourable to anyone, or other, of the involved parties. In fact, this Practice Note requires that all such reports are undertaken in accordance with the existing Practice Notes relating to the provision of expert evidence of the various Tribunals and Courts in Victoria. These existing Practice Notes make it clear that the expert’s paramount responsibility is to provide an independent, expert opinion to the Tribunal or Court; the expert does not have a responsibility to provide an opinion that supports their client’s case.
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A new application of radar in improving pile dynamic formulae used in the quality control of pile foundations
Installing piles into the ground is a very complex if not uncertain activity. This is particularly true from the point of view of proofing piled foundations. One of the methods currently available is the Dynamic or Energy Formulae that are the oldest and frequently used formulae in determining the bearing capacity of piles. The more recent methods are based on the Wave Equation Analysis and different formulations such as Case Method, TNOWave, CAPWAP® and TEPWAP were developed for pre-driving analysis and post-driving measurement applications. The energy or dynamic formulae, which were developed based on the Newtonian Impact theory, have been regarded as being unreliable and less accurate than the more analytical Wave Equation Analysis methods. The two main reasons for the poor performance of the dynamic formulae are that the hammer energy is assumed and that they do not take the dynamic resistance into account. The advent of new technologies in the construction industry has produced gradual improvements that have resulted in the dynamic method to be used on many projects with greater reliability. In this paper, a new application of radar called IBIS-S is proposed as well as site test results are presented using the Hiley, Gates and MnDOT formulae. The comparison of the results with the more rigorous PDA, CAPWAP® and the GRLWEAP™ analysis show that with the application of new and precise testing equipments, the dynamic formula can be used with greater accuracy than the Case method. It is also shown that the IBIS-S unit may also be used to estimate and evaluate the empirical parameters used in the CAPWAP® and GRLWEAP™ analysis. This approach enables evaluation of the pile capacity to be made more accurately using the dynamic equations.
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BIM to Numerical Modelling Interoperability for Geotechnical Design of Underground Metro Station
Building Information Modelling (BIM) is one of the important processes being adopted by the construction industry as it provides a collaboration platform in conjunction with technical standards for interoperability over the lifecycle of an asset. However, geotechnical analysis engaging numerical tools has yet to leverage the BIM benefits due to the lack of effective interoperability means, which not only results in unnecessary remodelling and rework at a cost of labour and computational waste, but also with possibility of errors, misinterpretation and omission of information. Using a trinocular underground station as an example, a workflow underpinned by heuristic techniques is proposed to enhance the interoperability between a BIM design authoring tool (Revit) and a numerical modelling tool (FLAC3D) for geotechnical analysis. A BIM-based multiple LoD (levels of detail) model framework is proposed to represent different information requirements for different purposes of BIM use throughout the project lifecycle. Leveraging the associated geometry and semantics, techniques of parametric modelling, data manipulation via visual and traditional programming are engaged to bridge BIM and numerical modelling for geotechnical analysis on different design scenarios. The simulated results are visualised through a backward automation cycle to Revit for design optimisation. The presented solution offers and automates an error-free design-to- design workflow solution and therefore enables efficient exploration of design scenarios and design optimisation.
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Melbourne Metro Tunnel Project – Numerical Analysis Of Anisotropic Rock Mass For State Library Station
The Metro Tunnel Project is delivering twin nine-kilometre rail tunnels in Melbourne, Australia. In addition to the tunnels, five new underground stations are being constructed. Two of the new stations – State Library and Town Hall – are complex cavern and adit excavations located in Melbourne’s City Centre which will directly connect to the existing City Loop Stations.
The State Library station, located predominantly underneath Swanston Street and a busy tram route, was surrounded by a mixture of modern, educational and heritage developments requiring the excavation sequence and primary support to be designed to ensure minimal surface impacts.
To simulate the anisotropic rock mass response to the excavation of the State Library Station, FLAC3D numerical analysis was undertaken. The analysis adopted the ubiquitous joint constitutive model approach and was used to assess the performance of the primary lining design and to determine the impacts the predicted ground displacements may have on the surrounding structures.
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Challenges to Digital Transformation in Geotechnical Engineering
The application of digital data and technologies in geotechnical engineering is not new; however, the use is sporadic and inconsistent among geotechnical engineering specialists and firms across the world. Further, this use is often limited to specific areas such as processing of field data during ground investigations and detailed numerical analyses of complicated foundation systems during design. There is a general lack of interoperability among the various digital tools and systems, which is inhibiting efficiency that could have been achieved otherwise using compliant platforms which can readily transfer data and models. This paper examines by way of examples where digital data and technologies are being used to increase efficiency in design and construction and enhance collaboration on construction projects. The paper explores the current state of the art and future potential opportunity to automate the whole geotechnical design process of capturing field data, generation of ground models, analyses and design, and visualisation of final solutions without the need for manual data entry at any of the intermediate stages. The level and stages where human input would continue to be required in geotechnical engineering are also reviewed, given the level of empiricism we still adopt due to significant gaps in our understanding of the variability of natural materials, behaviour of ground under loading and due to its complex interaction with other man-made materials and structures. In addition, a view is taken of the market driven barriers that might be limiting the efficiency of the geotechnical industry and the society in general, which could gain from the ongoing digital transformation.
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CPT in Antarctica
CPT is used extensively to determine material properties in soils and clays, however, it has not previously been used in hard polar snow. Therefore, existing CPT equipment was adapted for use in Antarctica to assess polar snow to depths of 10 m or more where resistances may exceed 10 MPa. Snow is a rate dependant material and numerous factors must be considered when interpreting CPT in polar snow, but valuable parameters such as snow shear strength, stratigraphy and relative density may be obtained using CPT in polar snow.
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Landslide impacts on the South Coast Railway during the 1988-90 El Nino event
Major landslides occurred along a 25 km length of the railway connecting Sydney and Wollongong, on the south coast of NSW, as a result of significant and long duration rainfall during the El Nino event of the late 1980s. The impacts commenced with the tragic event at Coledale in April 1988, involving a major embankment failure with two fatalities, and culminated in over 100 individual sites being activated along the route. These sites were mainly embankment failures, but also included rock cutting instability, which were identified and treated progressively under a risk priority and safety management system. The repairs, which cost in excess of $70M, were implemented over a number of years, and included an intensive track closure (track possession) of the South Coast Railway during January 1990. The management system was developed, in close association with SRA personnel, with an over-riding early-warning system linked directly to the railway control co-ordinator in Wollongong.
The paper presents an overview of the instability experienced on the South Coast Railway, and its remediation at the time, the links to antecedent rainfall, and the philosophy of the risk management system. A selection of case histories is given, with their associated monitoring, and a listing of back-analysed geotechnical parameters is provided for reference purposes.
The paper serves to document a presentation given to the Sydney Chapter of the Australian Geomechanics Society in June, 1991 and is intended to be factual as at that time.