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Suction caissons: A new offshore foundation concept
Suction caissons have been used increasingly as a new offshore foundation system in the last decade. This paper goes through a number of different practical uses of suction caissons to date, which demonstrate the advantages and benefits of suction caissons and explain the reasons behind their popularity in the offshore industry. Some results from an experimental study aiming to investigate the possibility of installing suction caissons in layered sand-silt soil conditions are also presented. In particular the soil deformation is discussed which, when suction is applied, can be traced using an image-based technique in a half-caisson model test.
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Three dimensional geotechnical modelling of abandoned bord and pillar workings
The paper reviews the results of investigations of the Borehole Seam with reference to the available historical data. The results show that the method of working and the height of the working section in some areas vary significantly from that reported in the 1908 Royal Commission on Earth Subsidence at Newcastle. Pillar stability analysis indicates a significant difference in the factor of safety (FoS) in areas of known instability and those where the workings have remained stable.
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Technical note: Tasmanian Rock Temperature
A side benefit to the measurement of rock stress using Hollow Inclusion (HI) Cells is the opportunity they present to gather data on rock temperature. In the course of compiling a recent summary of Tasmanian rock stress from HI Cell measurements undertaken over a 40 year period from 1975-2015 (Hills, 2020), a database of 33 measurements from nine sites across Tasmania was compiled. The data covers a depth range from 78-1625 m below surface at a vertical interval generally less than 40 m, with most data points the average of two or three separate observations.
This technical note serves to make the data available in the literature. It does not seek to discuss the potential for geothermal energy in Tasmania although it does provide a comparison with some published data that was obtained for that purpose. There is no associated heat flux or thermal conductivity information associated with the HI Cell data. However, it might prove useful in future planning of ventilation requirements and systems for underground mines and civil engineering projects in Tasmania.
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A Geotechnical Investigation Of Geomechanics In Queensland
A few common features in the practice of geotechnical investigations and reporting in Queensland are presented in this paper. The intent is to highlight some areas where the practice can be improved and /or to make others not from Queensland aware of some key geotechnical features underlying the practice.
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Pavement engineering in Perth
This paper presents an outline of pavement design and performance in Perth. Favourable subgrade conditions, relatively low cost pavement materials and thin surface treatments are typical in the Perth area and can result in relatively low cost pavements.
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A Geostatistical Method For Predicting The Spatial Variability Of Rainfall In Landslide Hazard Assessment: A Case Study On The Southern Fleurieu Peninsula, South Australia
This paper presents four methods for predicting the spatial variability of rainfall: the theissen polygon, inverse distance squared, isohyetal and kriging. These techniques were applied to an area on the southern Fleurieu Peninsula for use in landslide hazard assessment.
The theissen polygon and isohyetal methods recorded the largest prediction errors due to their dependence on having a large number of rainfall stations not available in the area. The inverse distance squared technique was more successful but was primarily restricted by the difficulties involved in incorporating elevation into the model.
The most successful technique was the multivariate geostatistical algorithm: kriging with an external drift (KED). This technique was able to account for spatially dependent rainfall values and elevation. Predictive monthly rainfall plots were calculated between 1997-2000 using the technique, based on data from the past 74 years. Rainfall values were largest in areas of high relief (Mount Lofty Ranges) and lower in the valley system (Inman Valley). High rainfall variability was shown to have a significant impact when predicting the likelihood of rainfall-triggered landslides in the area.
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Geotechnical aspects of karst within the Swan Coastal Plain, Western Australia
The occurrence of karst limestone conditions within Western Australia is not well recognised within the general community but can be of major engineering significance for developments that are impacted by it. The presence and engineering significance of karstic limestone on the Swan Coastal Plain has been recorded by local Engineering Geologists with the first officially published recognition presented in the 1:50,000 scale Environmental and Engineering Geology Series Yanchep Sheet in 1986. The Geological Survey of Western Australia (GSWA) mapping highlighted a significant, well defined zone of karst phenomena within Tamala Limestone extending from Joondalup to Two Rocks. Increasing pressure from urban development along Perth’s northern corridor lead to several “near miss” incidents which precipitated the incorporation of a requirement for all development applications within the City of Wanneroo to include consideration of the potential for karst.
To date, the published literature relating to karst on the Swan Coastal Plain has been limited to geological descriptions of the phenomena. Although the potential karst hazard is now widely recognised within the geotechnical community there has been very little published information relating to geotechnical design considerations and strategies for urban development within areas affected by karstic limestone relating specifically to the Swan Coastal Plain. Considerable work has been completed over the past decade relating to the identification of karstic ground conditions and geotechnical design strategies to manage potential risks. In addition, the existence of additional areas of karstic limestone has been identified within the City of Cockburn and City of Mandurah.
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Shortland Esplanade, South Newcastle Beach, Australia: A case study in rockfall risk management
Shortland Esplanade at South Newcastle Beach traverses a stunning scenic location, at the base of an imposing coastal cliff line and defined by a sea wall that adjoins the Pacific Ocean. The cliff line and the sea wall comprise constraints that dictate the geometry, operation and management requirements of the esplanade alignment.
The subject section of Shortland Esplanade has had a history of rockfall activity from the overlying coastal cliffs, one such episode of which prompted Newcastle City Council to close the esplanade to protect the public from ongoing rockfall hazards. GHD Geotechnics were subsequently engaged to provide the following services:
- Identification of rockfall risk mitigation options
- Quantification of rockfall risk (QRA) before and after mitigation
- Design and supervision of Council’s preferred mitigation strategy.
These aspects of this notable case study are described herein.
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Residential development on the New Volcanics: A case study of suspected barium contamination and soil amendment
As Melbourne expands to the north and west in response to growing demand for residential accommodation, soils developed on the Lava Plains (Geological Survey of Victoria, 1967), otherwise known as the New Volcanics (Cochrane, Quick & Spencer Jones, 1999), will be exploited. These soils are commonly shallow, alkaline and duplex, whilst the interspersed grey cracking clays pose significant constraints on building foundations and urban infrastructure due to their high “shrink-swell” nature. Rock floaters, clay fissuring, calcareous layers, sodicity and high electrolyte levels can serve as additional impediments.
The aforementioned soil characteristics also constrain garden development, landscaping and revegetation due to the presence of relatively heavy B-horizons with poor internal drainage, a relatively flat landscape with poorly-defined surface drainage, shallow heavy finely-textured topsoils and shallow calcareous bands which limit root propagation. The range of native and exotic plant species that can be planted in this landscape is limited, despite the need to improve aesthetics in order to attract residents.
Whilst the geological characteristics of soils on the New Volcanics are well understood and their limited potential as plant growth media recognised, the impact of soil chemical properties on some foundations, plant growth and heavy metal availability is not.
This paper describes the outcome of an investigation into potential barium (Ba) contamination of a 15 ha site located 18 km west of the CBD which threatened to stop the proposed residential development. Barium, as a trace element, concentrates in intermediate and acid magmatic rocks and its occurrence is linked with alkali feldspar and biotite (Kabata-Pendias, 2001). In soils in the natural environment, barium will generally occur as barium sulphate (BaSO4) due to the ubiquitous presence of sulphate ions. Some paint pigments contain barium salts and thus barium levels can be elevated on derelict land (Bridges, 1987). Barium is also associated with radio-active fall-out and nuclear waste. Barium sulphate is widely used as a safe tracer in medical practice due to the insolubility of the compound.
In conducting a soil survey for residential development where barium levels are found to be high it is essential to determine if possible why the levels are high, how widespread is the area impacted and whether anthropogenic input is likely. Of particular interest are the distribution of barium concentrations with depth and the association of barium with appropriate anionic concentrations. Evidence of site disturbance or encapsulation is also important as is the prospect of pseudo-stratification.
Knowledge of the availability of heavy metals for plants can assist the assessment of risk to humans from food chain transfers and contact with soil barium; fortunately there are well-defined relationships between pH and soil electrolytes that dictate this availability.
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Compaction trial for comparison of impact rolling and conventional rolling techniques for a large earthworks program in The Pilbara
As part of the development of a project site in the Pilbara, a large earthworks program will take place involving the placement of up to six metres of fill above the current ground level. Prior to commencement of bulk production filling, a compaction trial was carried out at the site to compare the effectiveness of impact rolling compaction techniques with conventional compaction techniques. Two different rollers, a 12 tonne impact roller and a 21 tonne single drum vibratory roller, were applied across two prepared fill pads.
Variables considered in the trial included: compactive effort, lift thickness, number of roller passes, and moisture conditioning. Significant geotechnical field and laboratory testing was carried out across the two pads to assess density with depth, prior to compaction and at various stages of compaction. The test methods used included density testing (nuclear density gauge and sand replacement methods) and in situ penetration testing including cone penetration testing (CPT), dynamic cone penetrometer (DCP) and Perth sand penetrometer (PSP). Settlement monitoring was also carried out prior to and following compaction.
This paper presents an overview of the trial methodology and results of the compaction trial in terms of compaction achieved by the impact rolling and conventional methods.