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Soil failure mechanisms associated with spudcan foundations on clay
In soft offshore deposit sites, the spudcan foundation used in jack-up rigs can penetrate up to 2- 3 times its diameter. The bearing behaviour of spudcans is directly related to the soil failure mechanism during penetration, hence the understanding of the soil failure mechanisms is important. In this study, a novel method has been developed in a drum centrifuge to examine the progressive soil failure mechanism during continuous spudcan penetration. This technique involves a model half-spudcan, a strong box with a transparent window and subsequent Particle Image Velocimetry (PIV) analysis to display the soil flows associated with spudcan penetration. A camera was also fixed above the spudcan to show the plan view of soil deformation. Two soil conditions were examined: (a) normally consolidated clay where strength increases linearly with depth and (b) clay with uniform or constant strength with depth. From this study, it was found that three distinctive soil failure mechanisms can be identified for the uniform clay: (i) surface failure; (ii) soil back flow; (iii) deep failure. The cavity formed during the initial penetration remained open until soil back flow occurred. There was no cavity formed when spudcan penetrated into normally consolidated clay. The lateral extent of soil deformation was 1.8 times the spudcan diameter in both uniform and normally consolidated clay.
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Volume 38, Number 2 βΒ Editorial, View from the Chair, and News
Table of contents, editorial and chairman’s column for Australian Geomechanics, Volume 38, Number 2.
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A study on the effects of abutment cyclic movements on the approach of integral abutment bridges
Abutments in integral bridges experience rotational cyclic movements as a result of the temperature induced changes in the longitudinal dimension of the bridge deck. Cyclic movements of abutments against and away from the retained backfill result in densification and volume contraction of the soil adjacent to the abutment wall. Consequently, the retained soil will experience settlement in the vicinity of the bridge approach in addition to an increase in the lateral earth pressure exerted on the abutment. The settlement of bridge approaches causes rideability and safety issues for bridge users while the escalated earth pressure may result in structural damage to the bridge abutment in the long term. This paper used the finite element method to investigate an integral abutment wall subjected to cyclic perturbations using the ABAQUS software. Two primary modelling cases were investigated. In Case 1, a finite element model was developed and verified against centrifuge test results of an integral bridge abutment before using it to study various factors influencing the response of the approach backfill subjected to cyclic rotational movement of the abutment. In Case 2, the finite element model was modified to incorporate the use of expanded polystyrene (EPS) geofoam in the approach backfill and it was once again verified against results from a laboratory experimental study. The modified finite element model was applied to study potential solutions using EPS geofoam to mitigate the soil settlement and to prevent the stress ratcheting at the interface between the backfill and the abutment. Results from the finite element study without and with EPS geofoam (Case 1 and Case 2 respectively) in the approach backfill subjected to cyclic rotational movement of the bridge abutment are discussed.
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Continuous Monitoring of Landslides and Infrastructure for Asset Management
The University of Wollongong Faculty of Engineering and Information Sciences Landslide Research Team (UoW), with our industry partners, Wollongong City Council, Roads and Maritime and Sydney Trains, has developed a network of thirty one currently active Continuous near Real-Time Monitoring (CRTM) stations within NSW.
This paper provides a general overview of the field monitoring equipment used, the monitoring strategies employed, wireless and mobile communications employed and a brief mention of the monitoring server setup and the related IT setup. The second part of the paper focuses a more detailed summary of two site installations, the acquired monitoring history and how this has expanded our knowledge and understanding of the site geological models and allowed progress towards site remediation and ongoing management. A brief mention of several interesting and emerging technologies in the fields of the Internet of Things (IoT) and Low Power, Wide Area Network (LoRaWAN) instrumentation is made.
The paper concludes by highlighting some critical issues related to the development of site monitoring strategies that experience has shown are sometimes not well managed. These include the reason for monitoring, the awareness of ongoing maintenance costs for the life of the monitoring, the duration of monitoring and reasons to either continue, modify and cease a monitoring program.
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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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Lateral behaviour of pile located on top of a slope
The study of a pile behavior on top of the slopes is one of the cases that has been attracted more attention these days. Usually, the behavior of lateral loading piles is studied on the slopes with a range of angles. One of the more important parameters in this field is the lateral bearing capacity of piles. The main aim of this research is to evaluate the lateral bearing capacity of piles under lateral loading. Evaluation of different situation is accomplished by changing the pile length and the pile distance to the slope crest in various slope angles. The pile lateral bearing capacity, horizontal and vertical displacements of the pile head in different slope angles are compared with the flat ground. It is shown that the lateral bearing capacity changes in different slopes are dramatically affected by both the length ratio of the pile to the slope height (L/H) and the distance ratio of the pile from the slope crest (X/D). When the distance ratio of the pile from the slope crest is equal to zero, a great difference is observed from all other cases.
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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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Understanding The Hydrogeology Of A Bauxite Residue Disposal Area
Worsley Alumina Pty Ltd (WAPL) has bauxite mining and refining operations in the Darling Range, near Collie, Western Australia. Bauxite ore refining residue (bauxite residue) is a waste product from the refining of bauxite ore to alumina.
Bauxite residue is a by-product of the Bayer process in which bauxite ore is physically and chemically transformed to extract alumina, leaving a viscous slurry by-product. The bauxite residue is dewatered to give a slurry of approximately 62-64% solids. The solids consist of combined sand and fine silt to clay sized fractions, of which iron (oxy) hydroxides are the dominant mineral. Before and after drainage, the residue remains alkaline, sodic and saline. Consistent with residue chemistry, the drainage liquor is alkaline, saline and contains humic substances.
Environmental legislation demands safe containment of the bauxite residue, which in this case is achieved by deposition into large dams, known as bauxite residue disposal areas (BRDAs), situated within the refinery lease. Worsley Alumina is legally bound to develop a decommissioning plan for their BRDAs. One BRDA in particular (BRDA1) is approaching decommissioning stage. A sound knowledge of the hydrogeology of this BRDA is essential for the development of a satisfactory decommissioning plan.
When BRDA1 is closed and rehabilitated, it will be capped with between 300 to 500 mm of soil and re-vegetated. An interception drain and capillary break will underlie the soil cap, so that it will be non-infiltrating (rather than “impermeable”).