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The dynamic behaviour of some fine-grained subgrade soils under traffic load
The flexible pavement is a very important infrastructure asset which normally consists of asphalt or a sprayed seal surface layer and the underlying base and sub-base courses. The subgrade soil is the existing soils and is the foundation of the pavement. It can be said that the performance of the pavement significantly depends on the bearing capacity of the subgrade. Therefore, an understanding of the behaviour of the subgrade soils would increase the confidence of pavement engineers in the design. Under the moving traffic load the behaviour of the subgrade soils contains two parts: resilient and permanent deformation. In order to investigate this behaviour in the laboratory repeated load triaxial equipment is used. Due to the complicated, time-consuming and expensive procedure, it is a challenge to perform the repeated load triaxial test as a routine basic test. Previous studies have reported the significant influence of the subgrade soil properties and loading conditions on the resilient and permanent deformation. In the current paper, the resilient and permanent deformation behaviour of several fine-grained soils collected from various locations in Victoria, Australia were studied. The effect of subgrade soil physical properties and stress conditions on the resilient modulus and permanent deformation for the experimental soils are examined and discussed.
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Geotechnical Aspects Of Dredging And Reclamation Works For The Port Botany Expansion Project
This paper contains a discussion of the geotechnical aspects of the dredging and reclamation design and construction for the Port Botany Expansion (PBE) project in Sydney, Australia. The project involved dredging approximately 11Mm3 of Botany Bay Sands to form the 63 Hectare (Ha) reclamation. Dredging and reclamation works for the project commenced in 2008 and were completed in 2010. The bulk dredging works were carried out using cutter section dredges and various reclamation techniques were used including land discharge (pipelines), spreader pontoon and aerial discharge (rainbow).
This paper examines the dredging work completed at PBE from a geotechnical viewpoint and describes issues faced during design and construction, including methods for identifying suitable source dredging material, practical dredging tolerances, design of disposal areas for unsuitable materials and stability of underwater cuts and fill slopes.
The paper also discusses the specification for ground improvement works completed for the reclamation, including the earthworks testing requirements and fill verification processes adopted. The potential for fines being included in the reclamation was a major risk to future performance of the reclamation and so the methods used to assess and mitigate this potential risk are discussed. The results obtained from different compaction techniques including dynamic compaction, vibrocompaction and impact roller compaction are also presented in the paper.
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Foundation design for underground Metro stations in Dubai
This paper is based upon the investigation and design stages for two of the 30 metre deep underground stations constructed in water-bearing sands and very weak rock as part of the initial development for the Red line of the Dubai Metro, United Arab Emirates (UAE). The paper firstly outlines the geological and hydro-geological conditions encountered at the City Centre and Burjuman underground stations designed by Hyder, with specific details of the geotechnical design parameters and groundwater data. The design criteria and constraints for the structures are subsequently discussed from a geotechnical perspective, in particular the issues of dewatering during construction and the impact of the long term uplift pressure after completion on the design solution. Two critical geotechnical design issues are the use of the tension piles/barrettes against uplift for the station box and load bearing barrettes for the viaducts immediately above the underground station structures. This paper also describes the progression from concept to detail designs and how the uplift issues were resolved and the lessons learnt.
Both empirical design methods and numerical modelling for the design of tension piles/barrettes are presented in the paper to emphasize the complexity of what at face value appears straightforward. The load transfer mechanism of the viaduct load through the barrette panels and their displacement compatibility with the station box slabs were analysed using both 2D analysis and 3 dimensional methods.
The permanent underground station box structures have now been completed and are in operation. The design assumptions were validated through the construction stage using an observational approach/monitoring, reflecting the effective and successful application of the design and decision making process.
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Behaviour of Clean AI Sand Under Triaxial Monotonic Loading
Adelaide Industrial (AI) sand has been widely used for land development and as a construction material in Adelaide, Australia. However, the mechanical properties of AI sand are not yet well understood. In this paper, the overall behaviour of AI sand is discussed initially, and then its characteristic features under drained and undrained triaxial shearing are evaluated for a wide range of initial void ratio, e0 (1.09 to 0.73) and mean effective confining stress, p’0 (50 to 400 kPa). It was observed that the undrained and drained behaviour of AI sand was significantly influenced by the initial state, i.e., e0 and p’0. Under undrained shearing, AI sand displayed normal soil behaviour, i.e., a higher contractive tendency with increasing p’0 for the same e0.The triggering of static liquefaction was identified by instability stress ratio, ηIS = q/p’ and it was observed that ηIS was influenced by both e0 and p’0. In drained shearing, the samples with low e0 showed higher stiffness as compared to samples with high e0 for a range of p’0 between 100 kPa and 400 kPa.
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Intelligent Prediction Models For UCS Of Cement/Lime Stabilized QLD Soil
The study aims to develop proposed predictive formulas for determining the unconfined compression strength (UCS) of cement/lime stabilized Queensland soil based on Multi-Gene Genetic Programming (MGGP) and Artificial Neural Network (ANN). The models evaluate the effect of three independent variables, including the binder type (cement and lime), the binder content, and the curing time, on the UCS of the stabilized soil. The results show that the selected optimal MGGP and ANN models can predict the target values with high correlation coefficients (R-value approximately of 0.992 and 0.998, respectively), and low errors (e.g., RMSE and MAE). The sensitivity analysis of the MGGP and ANN models provide the same results, in which the curing time has the greatest influence on the UCS value, followed by the binder content and binder type. The performances of the MGGP and ANN models are compared based on statistical parameters, several external criteria, and distribution properties. The study finds that both models show their generalization capabilities with robust, powerful, and accurate prediction ability; however, the ANN model slightly outperforms the MGGP model. The proposed predictive equations formulated from the selected optimal MGGP and ANN models could help engineers and consultants to choose the suitable binder and the reasonable amount of binder in the pre-planning and pre-design period.
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A method for the prediction of soaked CBR of remoulded samples from standard classification tests
Many authors in the past have investigated the ability of standard classification tests to provide an estimate of soaked CBR for remoulded samples across a wide range of materials with most classifications limited to fine grained soils with soaked CBR’s < 20. A method of estimating the soaked CBR of a remoulded soil from a PSD test and an Atterberg Limits test has been developed and tested against field data. It is valid for coarse grained or fine grained soils, or mixtures of both, and is not limited by the CBR value. The method also accounts for modified compaction of the material after soaking as the relative compaction prior to soaking did not influence the correlation. The method is based on more than 400 soaked CBR tests in a wide variety of soils from around Western Australia, South Australian and Northern Territory. The method has been compared against the results of soaked CBR test from several locations around the world and found to be comparable. The method is based on the Fine Material Factor (FMF) of the soil which is the product of the raw Plasticity Index and the proportion of the soil passing the 0.425 µm sieve. This method confirms the long held anecdotal evidence that materials with a FMF < 450 are typically suitable for sub-base use and in some cases suitable as base course. A series of correlations have been developed linking FMF and Soaked CBR for a range of MMDD Ratios.
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Mud pumping under railtracks: mechanisms, assessments and solutions
Mud pumping under railway tracks has received increasing attention from academic and practical perspectives in recent decades, however, the actual mechanisms and possible solutions are still not understood or well established. Frequent investigations in countries such as Japan, Canada, the USA, China, Australia, the UK, and other European regions where railway systems are the largest and most advanced, indicate that mud pumping still leads to high annual maintenance costs. On this basis, a thorough review is therefore essential, so this paper presents a systematic and comprehensive review of mud pumping in railways. In particular three primary aspects of mud pumping are addressed: (i) the phenomena and mechanisms; (ii) assessments; and (iii) solutions. The review shows the three essential factors that trigger mud pumping, i.e., excess fines, excess water, and cyclic loads. While excess fines can be induced by subgrade fluidisation, ballast breakdown and external sources, the excess water is mainly due to insufficient drainage in the foundations. Given these 3 factors, different contexts where mud pumping can be instigated are summarised such as subgrade fluidisation and infiltration, peat boils from soft roadbeds and upward migration of non-subgrade fines. Unfavourable weather condition, poor sleeper-ballast contact and stress/strain concentration at particular sections such as rail joints, switches, crossings and transition zones can accelerate the inception of mud pumping. In all cases, the generation of excess pore pressure is the driving mechanism. The study also summarises the laboratory and in-situ techniques currently used to assess mud pumping. 4 major groups of mud pumping solutions are highlighted with their advantages and disadvantages: (1) clean, modify and renew problematic layers; (2) enhance drainage condition; (3) geosynthetics; and (4) chemical stabilisations.
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Subgrade ground improvement using in-situ stabilisation for track formation in Melbourne
The Southern Program Alliance (SPA) is one of the alliances formed in Melbourne to remove level crossings, construct track duplications and upgrade the rail network as a part of the Victorian government initiative to improve rail infrastructure. An integral component of a rail infrastructure project is the construction of track formation. The essential requirement for rail formation is to satisfy the bearing capacity (strength) and settlement (serviceability) requirements for rail loading. The strength and serviceability requirements are a function of track design, axle-load, speed, and, notably, subgrade characteristics. For the SPA projects to date, where existing subgrade conditions could not satisfy these requirements, either the weaker subgrade was excavated and replaced by structural fill material, or subgrade improvement using in-situ stabilisation was explored. Subgrade improvement typically minimises the excavation and earthworks required for the construction of track formation and provides significant sustainability, cost, and time benefits to the project, without compromising the functional requirements. Subgrade stabilisation methods using admixtures (lime and cement) were considered and/or adopted for differing surficial geological deposits, including alluvial deposits, residual soil of Silurian origin and Tertiary sediments of South-East Melbourne. The design strategy was to verify the applicability of admixture ratios through laboratory testing, whilst further undertaking quality assurance (QA) measures through the construction phase. To assess the depth of stabilisation required, both empirical and finite element analysis design methods were undertaken. This paper summarises key design, laboratory testing and construction considerations for subgrade improvement works undertaken for a rail track duplication between Diamond Creek and Wattle Glen in Melbourne’s North-Eastern suburbs.
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Earthquake-induced landsliding in New Zealand and potential for landslides during earthquakes in Adelaide, South Australia
A study of landsliding caused by historical earthquakes in New Zealand was completed at the end of 1997. That study showed the minimum magnitude for earthquake-induced landsliding (EIL) in N.Z. to be M 5, with significant landsliding at M 6 or greater. The minimum MM intensity for landsliding is MM6 and the most common intensities for landslides are MM7–8. The threshold for liquefaction is MM7 for sand boils and MM8 for lateral spreading. Environmental criteria (landslides, liquefaction) were also defined for the MM Intensity Scale.
In this paper the EIL relationships and MM Intensity criteria are described and then applied in Adelaide. This indicates that an M 6–7 (MM8–9) earthquake in the Adelaide area could cause moderate to large rock falls and slides on high unsupported cuts, river banks, terrace edges and coastal cliffs. Liquefaction damage could also occur in areas of saturated sandy alluvium and estuarine deposits. The historical seismic record, however, suggests that the probability of an M 6 or M 7 earthquake in Adelaide is relatively low; hence the potential risk from earthquake-induced landslides and liquefaction is also likely to be low.
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Application of Statistical Techniques for Geotechnical Site Investigation and Design
Uncertainty is a universal and important aspect of geotechnical engineering and it is comprised of several different aspects. The most significant is likely that derived from spatial variability, where the properties vary from one location to another as a result of the processes that form the ground. Secondly, statistical uncertainty is a critical element of geotechnical engineering. Other important sources of uncertainty are those associated with the testing process itself, the transformation of the test results to design values, and uncertainties derived from human error. The paper discusses each of these uncertainties in some detail and provides examples and guidance on how to quantify and account for these in the geotechnical design process. The paper also presents two examples that demonstrate the power of statistical simulation in geotechnical engineering practice.