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Slope design process in a mining context
William Sarunic
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High-speed Railway Geotechnical Problems
Distinguished Professor Daichao Sheng
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Simulation of the cone penetration test: discrete and continuum approaches
The paper presents the modelling of the cone penetration test using two procedures: a discrete approach and a continuum approach. The discrete approach is based on the Discrete Element Method where a granular material is represented by an assembly of separate particles. Cone penetration has been simulated for both uncrushable and crushable sands. For the continuum approach, the Particle Finite Element Method has been adapted in order to overcome the difficulties posed by the occurrence of large displacements as well as by the geometrical, material and contact nonlinearities of the problem. Both single phase and two-phase (coupled hydromechanical) formulations have been developed and applied. Although not exempt from problems, both approaches yield realistic results leading to the possibility of a closer examination and an enhanced understanding of the mechanisms underlying cone penetration.
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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.
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Geotechnical characteristics of aged biosolids stabilised with cement and lime
Biosolids are the remains of the sewage treatment process, which are a mixture of both organic and inorganic compounds including household and industrial wastes. Recent attempts have been made to stabilize biosolids with special admixtures, in order to improve their geotechnical properties. The aim of this paper is to report the results of a geotechnical laboratory investigation on waste-water biosolids stabilized with different percentages of cement and lime. Biosolids were sourced from the Western Treatment Plant (WTP) in Melbourne, Australia. Compaction, California Bearing Ratio (CBR), swell, hydraulic conductivity, consolidation, creep and triaxial tests were carried out on the compacted specimens. Both static and standard proctor compaction methods were used to prepare the test specimens in this research. The results suggest that the permeability values of biosolids decrease consistently by increasing the amount of lime and cement. In addition, increasing the amount of additives decreased the compression potential of biosolids. The strength of the biosolids samples increased with the addition of lime and cement but the highest shear strength was achieved with 3% cement. This paper concludes with a discussion of possible applications of the stabilized mixture in road embankments.
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Numerical modelling of ground loop configurations for direct thermal applications
The rigorous design of direct geothermal heat pump systems that use concrete piles or boreholes as heat exchangers to extract or reject heat with the ground needs a model for the thermal process in the ground, the ground heat exchanger (GHE) and the carrier fluid circulating within. Thermal interference between pipes in the GHE is an important factor which may significantly affect system efficiency. Different pipe configurations including single U-Pipe, double U-Pipe and double cross U-Pipe, are modelled using finite element methods to investigate the thermal interference that occurs between the pipes within the GHEs. In this work, water is the carrier fluid circulating through the pipes and exchanging heat with the ground. Water inlet temperatures and ground far-field temperatures were chosen as being typical for Melbourne conditions. U-Pipes are located vertically in concrete piles or grouted boreholes surrounded by the ground. The efficiency of the GHEs is investigated in heating mode. The results presented confirm the importance of geometry in design and the significant variations in performance that can be obtained using different pipe configurations.
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Effects of geotextiles on drainage performance of ballasted rail tracks
Naturally soft soils are mostly found around coastal regions, where the construction of ballasted rail tracks is required to have a more thorough consideration regarding filtration. Any poor filter design on weak ground inevitably leads to a critical change in ballast characteristics. It is noticeable that such a change results in several issues including significant migration of finer particles about the subballast-subgrade interface and the deficiency of subballast filtration. These problems eventually reduce the drainage ability of the rail sub-system and may cause severe damage which can only be remedied by frequent and costly track maintenance. It is therefore important that geosynthetics such as geotextiles are introduced to the rail track system as an additional filter layer, which is able to retain the desirable filtering characteristics. This paper investigates the impact of non-woven geotextiles on filtration behaviour of subballast in the laboratory, while adopting different granular filter (subballast) thicknesses varying from 0 mm to 50 mm. The research findings demonstrate a notable difference in the cumulative fine loss per unit volume within a given period of time between two distinctive tests – with and without geotextiles, thus emphasising the beneficial application of this geosynthetic material. Empirical estimation of permeability and properties of subballast, including grading curves after testing, are carefully carried out and the results are presented in this paper. The results indicate that the thickness of granular subballast can be significantly reduced by including geotextiles. This paper, in turn, evaluates the potential combination of the track substructure and geotextiles to achieve the optimum filter design and more importantly, alleviate the cost of track maintenance.
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Rockfall risk and remediation on the Lake George Escarpment
In 2005 a rockfall occurred on the Lake George Escarpment, north of Canberra in New South Wales causing rocks to be strewn across the Federal Highway. Although vehicles were not hit by the fall, a significant traffic accident ensued as vehicles attempted to avoid the debris on the highway. The escarpment had not been previously recognised as a site prone to rockfall with no recorded or published history of rockfalls. A subsequent investigation involved the use of photogrammetry, geomorphological and geotechnical mapping, and computer rockfall simulations to assess both the extent of rockfall hazard across the escarpment and the risk to road users. The assessed risks at the site exceeded the tolerable risk level stipulated by the NSW Roads and Traffic Authority (RTA). Slope remediation works involved the partial removal of the rockfall hazards by blasting and manual removal in conjunction with the construction of a series of rockfall fences to reduce rockfall risk to tolerable levels. This paper provides a commentary on rockfall trials filmed with high-speed motion cameras that were conducted to calibrate rockfall simulation software and assess the fence requirements. The paper also provides insight into natural hazards with the potential to affect transport corridors that should be considered at route selection stage.
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Geotechnical design of Main Creek Tailings Dam
The Main Creek Tailings Dam at Grange Resources Savage River Mine is a good example of a large tailings dam being constructed using the upstream construction method.