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An evaluation of the tilt test for granular materials
Studies into rockfill have advocated the use of a tilt test to characterise the shear strength of coarse granular materials. The tilt test employs a simple split box, which is filled with rubble and then tilted until the upper box half slides off the lower box half. The angle at which this occurs is related to strength characteristics of the tested material, but the interpretation of this result is less than straight forward. This paper describes a systematic study of the tilt test on a series of gravels and mine wastes. The research shows that the tilt angle is sensitive to the tilt rate and the water content of the spoil, but that if the test is carried out in a systematic way, consistent results can be achieved. The results show that the tilt test is not a good discriminator of shear strength in waste rock materials. The tilt test is very sensitive to particle size, particle shape and relative density, but because of its very low confining stress, it is insensitive to the physical strength of particles. This means that the tilt test fails to discriminate reliably between weaker and stronger waste rock materials, for materials that are subjected to any significant amount of confining (normal) stress. It cannot be used as an alternative to direct shear testing to determine the shear strength parameters of mine spoil materials.
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In-situ Waste Characterisation For Primary Settlement Assessment For High Embankment Built Over Municipal Solid Waste
Due to land restriction, some sections of several highway and railway projects have to be constructed over poor and uncommon foundation such as waste materials placed as part of the preceding landfill operation. Waste/Municipal Solid Waste (MSW) materials especially those comprising high amount of organic and readily degradable materials are highly compressible and have high variability in composition and void distribution. Conventional geotechnical laboratory testing and limited in-situ testing are often insufficient to characterise waste material. A design of field trial to understand the settlement characteristics will also require a reasonable understanding of the properties of waste materials.
This paper presents a basic methodology for in-situ characterisation of waste materials to enable the assessment of geotechnical properties of these materials on the basis of their composition and organic content. This includes the selection of suitable drilling method to allow for a good quality and continuous waste sample recovery. From such characterisation, a dimensionless Waste Compressibility Index (WCI) can then be derived based on procedures given in the published literature. The WCI value can then be correlated with compression ratio used to analyse primary consolidation settlement.
A case study is presented in this paper where a railway embankment was to be built over a landfill foundation consisting of existing Municipal Solid Waste (MSW) in the east coast of Australia. The foundation was treated by means of high surcharge. The abovementioned methodology has been used in the design to characterise MSW materials and assess primary settlements. The back-analysis by using settlement monitoring data indicate a reasonable agreement between the WCI related to the back-analysed compression ratio and the estimated WCI values. This agreement was obtained despite the variability in the aforementioned correlation. It shows that a basic methodology for in-situ waste characterisation on the recovered waste sample was able to provide a reasonable estimate of compressibility parameters for the purpose of analysing primary settlements.
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Settlement characteristics of deep engineered fills
The long-term settlement characteristics of engineered fills are generally not a significant concern where the fill thickness is less than a few metres. With the increasing scarcity of land for urban and commercial development and the availability of large volumes of excavation materials, sites are being considered for development that previously would have been filled with refuse of other uncontrolled material and left undeveloped. For such sites, including backfilled quarries, the long-term settlement characteristics of the fill becomes an important consideration.
In this paper the settlement of engineered fill has been characterised as having four potential components:
- Short-term Settlement, which occurs due to self-weight as the fill is placed and for a relatively short time after fill has reached full height.
- Elastic Settlement, which occurs in the fill when subjected to loads from footings and floor slabs.
- Long-term or Creep Settlement, which occurs over a period of years. In the case of deep fills with light building loads, the creep due to the self-weight of the fill will be the major component of the long-term settlement.
- Hydroconsolidation (Collapse) Settlement, which can occur and is due to saturation of the fill.
This paper presents data on the settlement characteristics of deep fill with emphasis on the characteristics of engineered fill (i.e. fill placed and compacted in relatively thin layers to an engineering specification).
Data derived from laboratory testing and field monitoring is provided for a variety of materials placed as deep engineered fills for a number of projects in the Sydney Region.
Settlement estimates derived from parameters obtained from a desk study of international literature and some data from the Sydney Region are presented and compared with the results of more recent laboratory testing on materials from the Sydney Region.
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Optimising the pattern of semi-rigid columns to improve performance of rail tracks overlying soft soil formation
With Australia facing a rapid increase in population in the next 30 years, the government is being proactive in handling the forecasted growth. The release of 2010 Metropolitan Transport Plan by the New South Wales (NSW) Government shows that the State of NSW will see an increase in commuter travel by rail. The NSW rail system is one of the most complex networks in the world and due to population growth, the network will require further expansion with construction of new railway lines partly on weak and marginal ground and will also require more frequent train running on existing lines. This study seeks to identify the effectiveness of semi-rigid inclusion ground improvement techniques particularly stone columns and deep soil mixing in controlling settlement of soft soils when placed under the dead loads of the rail structure and the large live loads of freight trains. The employed numerical study assesses the relationship between the column position in the track cross section and the overall settlement of the ballasted rail formation. The numerical results show that the overall settlement of the track reduces significantly with the use of columns close to the centre of the track and not just under the rail. In addition, application of one layer of geogrids between sub-ballast and sub-grade assists to reduce the maximum settlement of track decreasing the future maintenance costs.
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Linking Design With Specification Of Geotextiles
Geotextiles usually make up a fraction of the cost of an engineered structure and are primarily incorporated in the stabilisation or strengthening measures in the foundation or base of the structure. As such, the design of these geotextile used in any structure is critical to the long term life of the structure. While geotextile design methodology is reasonably well understood the correct specification of the geotextile is often overlooked or poorly understood and implemented. A poorly constructed specification will often result in installation of a geotextile which bears little or no resemblance to the geotextile which was originally designed. This often leads to poor performance and associated high maintenance of the structure and at worst failure.
Many of the geotextile test methods have been adapted from the general textile industry and can not be directly related to the engineering functions that geotextiles are designed to perform. Different test methods throughout this document are described as either an Index test or a Performance test. Index test results are obtained quickly, with good reproducibility, which permits the comparison of one product to another and are ideally suited to the manufacturing quality assurance process. Performance tests allow direct assessment of the likely in-situ interaction between the soil and a geotextile.
Therefore, understanding the intricacies of the test methods and how they relate to the application of the geotextile is the key to the project. This document will attempt to improve the understanding of the relevant test methods and their application.
Understanding the test method alone is not sufficient to ensure the correct product is supplied. The designer must understand how the information presented in manufacturer’s data sheets is compiled and how this relates to the product supplied to site. It is critical that designers can interpret individual test results obtained as either Manufacturing Quality Assurance (MQA) or Construction Quality Assurance (CQA) as failure to correctly interpret results can lead to incorrect acceptance or rejection of products supplied.
In an attempt to cover all the issues raised above the following topics will be discussed in some detail
- Relating function to test method
- Test methods overview
- Data sheet interpretation
- Conclusion
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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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Elements of expansive clay roadway specifications
Technical specifications provide guidance on quality levels and documents the procedures to be followed to achieve an acceptable standard. Road specifications sets out the precise requirements of the road authority and varies between Australian States and Territories, and internationally. A road construction specification cannot be overly prescriptive as it must integrate standard procedures, with varying climatic and material conditions as well as the significant testing variability. Elements used in developing road specifications using expansive clay material is presented.
A key quality control parameter is density. Soil compaction control requires a lower characteristic value to obtain the required density (and associated implied increase in strength and modulus with increased density). However, increased density can result in higher suction and swell for highly expansive clay soils. An upper characteristic value needs to be considered for such materials. The Optimum Moisture Content (OMC) is associated with the Maximum Dry Density (MDD). For expansive clays, the Equilibrium Moisture Content (EMC) is more important than an OMC placement target. Thus, the standard compaction approach which applies to non-expansive material cannot be directly used to expansive soils because such soils are dependent on climate, which influence its soil suction and movement potential. Movement rather than strength often governs for expansive soils. Zonal strategies are appropriate for embankment constructed of expansive clays.
Additionally, residual soils are very common in Australia, with a high granular content in “clayey” soils. The commonly used Plasticity Index (PI) used as an initial indicator of likely expansive behaviour, is not representative of the whole sample, with a significant “error” in this most basic of classification tests when used as a screening measurement to identify expansive clays in Australia. This screening is the first step in establishing appropriate design and construction procedures. The weighted plasticity index (WPI) accounts for the portion used in the PI test and this is more relevant for classification of residual soils. A simple ± 2% of Optimum Moisture Content (OMC) which may be relevant to nonexpansive materials cannot be applied to expansive clays. Additional testing variabilities also apply, which influences the interpretation of the reference maximum dry density (MDD) and even the CBR values used.
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Spatial and statistical distribution models using the CBR test
The California Bearing Ratio (CBR) is the most common test used in the design of pavements. This simple test has many pitfalls in its application. This is an empirical test, and one must be aware of its many considerations if the design value is to be appropriately applied.
A design value must consider its spatial variation, level of compaction and its relationship with its surrounding layers. The design risk is used to determine the characteristic value for a given project. Characterisation using the spatial and statistical variation of a CBR is used for a project site in Queensland to illustrate the requirement to use an appropriate prediction model. The results of this curve fitting show the normal distribution is inappropriate due to negative values and the lognormal distribution is an appropriate statistical model to characterize the design CBR.
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An Innovative Geotechnical Monitoring System For Soft Ground Treatment On W2B Pacific Highway Upgrade Project
This paper presents an innovative geotechnical monitoring system for soft ground treatment for the on-going Woolgoolga to Ballina (W2B) Pacific Highway Upgrade project. This $4.3 billion project is Australia‟s largest regional infrastructure project and will upgrade about 155 kilometers of highway to four lane, divided road. The project starts about six kilometers north of Woolgoolga (north of Coffs Harbour) and ends approximately six kilometers south of Ballina.
One of the major challenges on this project is the construction of road and structures over soft compressible ground with a total length of over 25 kilometers in 1 to 2 years‟ time. During construction, the short term slope stability and settlement performance will be monitored by a total of 1500 instruments taking up to 10 million measurements. This will enable the team to take early preventive actions to maintain slope stability, to protect public safety and existing structures during construction, and to ensure that the projected long term settlement is within acceptable limits.
Following the standard file based approach, the instrumentation data was estimated to produce up to 80,000 files to be manually handled. To efficiently process the data, limit the potential for manual errors and reduce the turnaround time, Pacific Complete developed an instrumentation and monitoring (I&M) system using its project integration platform, automatically warehousing the data on the project servers and presenting real-time dashboard to the team using Qlik Sense and its GIS extension. In addition to providing high availability, transparency and reliability of the information, this system is expected to realize savings of $2.5M in manual handling of the information alone. The system can be progressively extended to support direct data download from automated instruments, more instrument types, single and multiple instruments alerts, and refined graphs to suit the requirements of linear infrastructure geotechnical monitoring.
Compared to the traditional copy and paste method using Excel, the benefits of this I&M system include fast processing of massive data on a daily basis, automatic integration with GIS maps, chainage, instrument type and locations, lateral displacement plots, settlement plots (both predicted and measured) in longitudinal sections, ratios of lateral to vertical displacement and fill height plots, pore pressure plots and existing road/structure movement plots.