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The contaminated land industry in Melbourne
Since the publication in Geology of Melbourne (Withers & Lane 1992) there have been significant changes in the assessment, remediation and management of contaminated land in Victoria. These changes have resulted in greater public interest in contaminated land issues, increased regulatory control and, perhaps most importantly, improved technical capability of the contaminated land industry. Specific regulation has also developed around the management of acid sulfate soils.
The purpose of this paper is to outline some of the key changes in the geo-environmental industry since 1992 from a regulatory and technical perspective. Much of these changes have come from significant changes in policy over this period which have been developed in parallel with a growing awareness of the issues presented by natural and anthropogenic contamination of the environment and an increasing awareness of need to protect our environmental resources such as ecosystems, land, surface water, groundwater and the air.
Brumund (1994) in his paper to the First International Congress on Environmental Geotechnics in Edmonton stated:
“Some markets served by civil engineers are relatively independent of regulations, some are influenced by
regulations, and some markets are largely created by and driven by regulations. The field of environmental
geotechnics falls largely in this last category”.The last decade of practice in environmental geotechnics in Victoria has seen the development of extensive policy, regulation and guidelines, to the point where the practice in Victoria is predominantly a regulatory driven industry.
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Transition treatment design for bridge approach embankments – from a practitioner’s perspective
Transition treatments in soft soil are implemented for the purpose of achieving differential settlement criteria between a rigid piled abutment and an approach embankment founded in soft soil. With carefully designed transition treatments, bridge abutments and their supporting piles can be constructed early in the construction program without the need to wait for embankment settlement to conclude – thus, facilitating an efficient construction process.
Methods to reduce or control settlement, include the use of piles/columns in the embankment foundation, and other ground improvement techniques such as preloading/surcharging. Piles/columns are used in varying frequency and quantity within the approach embankment to achieve the desired transitional effect and “protection” for the abutment piles from the lateral movement of the foundation soils. Overburden loads are often transferred to the piles/columns through a gravel mattress embedded with geotextiles, commonly referred to as a load transfer platform (LTP). The design of LTP’s depends heavily on the degree of support provided by the soil matrix surrounding the pile/column treatment.
The success of transition treatments can be measured by the magnitudes of settlement within the transition zone and achievement of differential settlement criteria. Methods to reduce long term creep settlement include the use of surcharging pressures to over-consolidate clay soils. In this paper, the measurement of differential settlement in the form of change-in-grade (CIG), i.e. change of slope between two straight lines, are discussed and clarified – removing some ambiguities and confusion which currently exist in practice.
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The Influence Of Bagasse Fly Ash Particle Size In Controlling Expansive Soils In Combination With Hydrated Lime
Sugarcane is the second largest export crop in Australia. Industrial production of sugar, from sugarcane, results in bagasse fly ash (BFA), a by-product from the cogeneration in sugar milling operations that generate electricity by steam. The chemical and physical properties of BFA highlight its potential as a promising pozzolan for the stabilization of expansive soils, due primarily to a high content and surface area of the amorphous silicate found in BFA. Silicate in bagasse fly ash reacts extensively with calcium hydrate in lime to produce hydrated products via pozzolanic reactions, this results in a hardening of the material to which BFA and lime have been added. This reaction has been studied to be a function of the size of BFA particles and conditions of the curing process.
This study explored the variables that influence the reaction and evaluated shrinkage and compressive strength of the mixtures to which bagasse fly ash, in the form of different particle size distributions, and hydrated lime are added. The maximum BFA particles sizes considered within this study include 75, 150 and 425 ÎĽm; curing times of 7 and 28 days are also explored. A suite of testing, including Atterberg limits, linear shrinkage (LS), and unconfined compressive strength (UCS) tests were completed on the prepared mixtures. The findings indicate that bagasse fly ash with a maximum size of 425 ÎĽm yields a higher UCS and lower LS, compared to finer BFA particle mixtures. The ash with a maximum particle size of 425-ÎĽm also improves the ductility of treated soils and accelerates their strength gain, compared to soil- lime stabilized samples. The results of the study build towards a better understanding of BFA, and the ways in which such a material maybe engineered to replace concrete in road work projects and other applications involving expansive soils.
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Evaluation of the Tasmanian North-West Coast landslide map series against the AGS 2007 Landslide Zoning Guideline
This paper documents an assessment of the recently produced Tasmanian Landslide Map Series in Tasmania’s North-west Coast region against the AGS 2007 Landslide Zoning Guideline and Commentary. In addition, comments are made on the Guideline and Commentary from the perspective of a practitioner using these documents.
Mineral Resources Tasmania (MRT) welcomes the introduction of the Guideline, and its Commentary, and have striven to adopt them as far as practically possible within the constraints of our project. The Guideline and Commentary provide a conceptual architecture and standard terminology for the practice which has been largely accepted by MRT.
Using the Guideline’s criteria we have classified the MRT maps as suitable for local and regional development because of its medium scale. Our landslide inventory is at the intermediate zoning level and our susceptibility mapping at the preliminary zoning level, which confirms the maps general intention and suitability for regional zoning purposes. MRT has used a combination of largely heuristic and deterministic transforms to create its susceptibility maps. The combined approach is more complex than the conceptual descriptions contained in the Guideline but this is in keeping with other published examples.
The experience gained by the production of regional scale maps at MRT enables the authors to comment on the usefulness of the Guideline and Commentary. Landslide zoning is a challenging exercise that requires considerable effort, skills and resources to put into practice. From the perspective of practitioners, it is the observation of the authors that some aims, realistically, may not be attainable within the constraints of most regional projects. Furthermore, the science underpinning the practice of landslide zoning is rapidly evolving and this requires the practitioner not to rely on the Guideline alone but to keep abreast of developments that are typically only published in the international literature.
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West Pilbara Iron Ore Project, Port off-loading facility, Anketell Point, Western Australia
API Management Pty Ltd (API), a 50/50 Joint Venture between Aquila Resources and AMCI propose to construct a multi-user port off-loading facility at Anketell Point in the Pilbara region of Western Australia, which will form part of the West Pilbara Iron Ore Project (WPIOP). The port off-loading facility will have an initial iron ore handling capacity of 30 million tonnes per annum.
This paper describes the nearshore geotechnical investigations that have been completed at Anketell Point. It outlines the purpose of the investigations and provides a geotechnical account of the planning, occupational health and safety and operational aspects of the investigations that led to the successful completion and factual geotechnical reporting of the investigations within program and budget. An overview of the logging, field testing, on site sub-sampling, laboratory testing and the ground conditions is provided.
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Performance and prediction of marine clay treated with vacuum and surcharge consolidation at Port of Brisbane
During the past decade, the application of vacuum preloading for stabilising soft coastal clay and other low-lying estuarine soils has become popular in Australia. The cost-effectiveness is a major factor in most projects in view of the significantly reduced time for achieving a relatively high degree of consolidation. Due to an increase in trade activities at the Port of Brisbane, new facilities on Fisherman Islands at the mouth of the Brisbane River will be constructed on the new outer area (235 ha) adjacent to the existing port facilities via land reclamation. A vacuum assisted surcharge load and conventional surcharge scheme in conjunction with prefabricated vertical drains was selected to reduce the required consolidation time through the deeper subsoil layers. The performance of the combined vacuum and surcharge fill system and the construction of the embankment are described in this paper. A comparison of the performance of the vacuum combined surcharge loading system with a standard surcharge fill highlights the clear benefits of vacuum consolidation. Field monitoring data are presented to demonstrate how the embankment performed during construction. The paper also evaluates the relative performance of the two contrasting preloading systems (i.e. vacuum and nonvacuum system). An analytical solution for radial consolidation considering both time-dependent surcharge loading and vacuum pressure is proposed to predict the settlements and associated excess pore pressures of the soft Holocene clay deposits.
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Case study: Impact of jet grouted column variability on a base block in sand
To construct an underground rail dump station at a port on a land reclaimed island in Australia, diaphragm walls and a base block designed of overlapping jet grout columns was used, aiming to allow excavation without dewatering. The base block varied between a depth of 8.9 and 19.4 m (surface RL ~6 m AHD) with material mainly consisting of sands. Proximity to the harbour provided a groundwater head boundary, with typical levels of 2 m AHD. Jet grout columns were designed with diameters between 2.1 and 2.7 m and a trial at the site was performed prior to construction. Failure of water tightness tests prior to excavation resulted in a second layer of jet grout columns being installed immediately below the original base block. During excavation of the material within the dump station gaps in the base block led to boiling of the sand, often before the base block level was exposed, preventing further excavation or construction. Ultimately an external dewatering and reinjection system was required to allow further excavation and construction of a concrete base slab on top of the base block. Investigation post construction by PSM highlighted the importance of jet grout column trial interpretation, the influence of column diameter, tilt and position variability and the consequence of small gaps in the base block. Monte Carlo techniques, based on observed as-built column variability, were used to demonstrate the impact of variability on the continuity of the base slab. These indicated that near perfect construction was required if the project objective was to be achieved.
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Geotechnical modelling of station caverns for the Epping to Chatswood rail line project
The Epping to Chatswood Rail Line project comprises a twin rail tunnel, three new underground stations and the upgrading of one existing station. The station caverns intersect a sequence of horizontally bedded shale and sandstone. The major rock defects consist of bedding planes, bedding plane seams, low angled cross bed partings and sub-vertical joint sets. Local experiences in the Sydney Basin have indicated that the behaviour of the defects and their interaction with the roof support system are critical to the performance of underground excavations. Another key geological feature that can have significant performance impact is the relatively high locked-in in situ lateral stresses.
Each of the new stations comprises a large span platform cavern, an adjoining concourse cavern, associated escalator shafts and service buildings. The design roof support system is cable bolts with cement grouted end anchorage. The interaction between the bolts and the jointed rock mass within the influences of the various facilities is complex and thus rigorous modelling was employed. This modelling included 3D distinct element and boundary element analyses and 2D finite element approach. The complexity of the numerical models varied from homogeneous rock to layered rock with various discontinuities. Furthermore, both end-anchored and fully grouted bolts have been incorporated.
Various parametric studies were undertaken to assess the effects of various model components (rock mass, defects, in situ stresses, sequencing and roof support installations) on cavern performance. Based on the modelling results, a system of rock bolts and construction staging has been adopted to optimise the permanent support system.
This paper is confined to the geotechnical modelling aspects of the project and presents the geological setting and the various analytical procedures undertaken. The results of the parametric studies and their impact on the final selection of the support systems are also outlined.
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Nonlinear response of 20 laterally loaded piles in sand
Closed-form solutions and their associated spreadsheet program (GASLFP) were developed by the first author for laterally loaded free-head piles in elastic-plastic media. The solutions show behaviour of a laterally loaded pile is dominated by net limiting force per unit length (LFP) fully mobilised along the pile to a depth called slip depth. They are characterised by three parameters of Ng, αo and n (to describe the LFP) and the soil shear modulus (Gs). Conversely, these parameters may be deduced by matching the predicted with measured response.
To facilitate practical design, in this paper, the input values of Ng, αo, n and Gs were deduced in light of measured response of 20 piles tested in sand. The result allows effect of pile types, installation action, and dry or submerged sand to be clarified. In addition, using analogy to pipeline-soil interaction, a new alternative expression described by the parameters kp, αo and n is proposed to construct the LFP. The use of the previous parameter Ng and the new kp is discussed at length. Critical responses for typical deflection levels have also been provided. This back-analysis is elaborated via three typical cases.
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Recent experiences in design and construction of high consequence temporary soil nail walls
This paper describes some of the authors’ recent experiences in the design and construction of high consequence temporary soil nail walls.
Various approaches to designing soil nail walls are discussed, including an approach recently adopted by the authors which is considered to be consistent with a limit state design intent.
However, it is reasoned that, regardless of which design approach is adopted, often “construction” aspects are far more significant than “design” aspects in determining how a soil nail wall performs. Three examples are used to demonstrate this point. By “construction” aspects the authors mean effects and deformations resulting from construction activities that are not typically explicitly accounted for in the analysis process, for example deformations from drilling and cleaning holes, vibrations, and small scale / temporary face instability e.g. slumping of interim unsupported excavation faces prior to shotcreting. By “design” aspects the authors mean the deformations of the soil nail wall due to stress relief resulting from progressive excavation of material in front of the wall, i.e. those that can be calculated using analysis.
The paper concludes that a complete soil nail wall design should consider not only the results of the analysis undertaken, but also address issues that may arise related to the construction of the wall, in order to achieve a successful outcome. Some observations and recommendations are made regarding how a design can address these “construction” aspects. It is concluded that the success of a high consequence temporary soil nail wall depends not only on the interaction between the soil and the structural elements, but also their interaction with construction aspects, and therefore a design should seek to address these aspects so far as practical.