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Geotechnical and chemical characteristics of ETP and WTP biosolids
Stricter regulations on the quality of wastewater treatment by-products are giving rise to an increasing volume of stockpiled biosolids. The annual production of biosolids in Australia is approximately 300,000 dry tonnes, which involves a biosolids management cost of about $A90 million. Biosolids are the end product and the main solid component collected from the wastewater treatment process. This paper presents some of the geotechnical and chemical properties of two samples of biosolids collected from Melbourne Water’s Eastern Wastewater Treatment Plant (ETP) stockpile No. 22 and the Western Wastewater Treatment Plant (WTP) stockpile No. 10. Various geotechnical tests – liquid limit, plastic limit, particle density, particle size distribution, organic content, and linear shrinkage – were undertaken. In addition, chemical tests comprising leachate analysis for heavy metals and chemical composition were conducted on the samples of biosolids. From an environmental perspective, all the samples of biosolids were found to be safe in terms of leaching for use as a landfill application material. The experimental results showed that the ETP biosolids have about 7% of organic content with some of the geotechnical and chemical properties similar to a conventional soil with similar particle size distribution. In addition, empirical relationships were obtained for the compaction behaviour of the ETP biosolids and a comparison soil used in this study. The results obtained in this study can be used as a guide for the use of ETP and WTP biosolids in different civil engineering applications.
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Green Square — Enabling Urban Renewal Through Smart Retaining Wall Design And Trenchless Construction
Green Square is one of the City of Sydney’s key urban renewal precincts, which is being transformed from old industrial land into a major new residential, retail and cultural hub. The Green Square Stormwater Drain (GSSD) is the culmination of a strategic alignment between City of Sydney and Sydney Water to provide flood protection in the Green Square area. Through a process of optioneering and hydraulic analysis, a new 2.5 km long underground drain consisting of multiple 1800 mm diameter pipes was installed by microtunnelling, and an open trench box culvert was replaced with channel widening via an anchored retaining wall in the final 300 m from Maddox St to Alexandra Canal. The new drain augments the existing trunk drain system and reduces flood hazard, allowing Australia’s largest urban renewal project to proceed.
The channel widening section of the GSSD was originally intended to be constructed into the bank of the existing open channel. A constructability assessment for installation of the box culvert within the narrow corridor between the existing open channel and adjacent buildings indicated that open trench box culvert construction would not be cost effective. This paper describes an innovative solution, where the existing channel was widened using an anchored retaining wall, replacing the proposed box culverts.
The trenchless (microtunnel) solution offered an alternative, value for money approach with significantly reduced environmental impact and achieved comparatively minimal community disruptions.
This paper also describes the ground engineering challenges and solutions employed on the site which included difficult ground conditions, landfill and addressing impacts of wall construction on adjacent infrastructure such as roads, bridges and buildings. Ground engineering risks were successfully managed through detailed scoping of investigations, numerical modelling of designs and adoption of observational methods during construction. The specification requirements, design, installation, monitoring and performance of the successful microtunnel drain and anchored wall system are discussed.
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Green Square – Enabling Urban Renewal Through Smart Retaining Wall Design And Trenchless Construction
Green Square is one of the City of Sydney’s key urban renewal precincts, which is being transformed from old industrial land into a major new residential, retail and cultural hub. The Green Square Stormwater Drain (GSSD) is the culmination of a strategic alignment between City of Sydney and Sydney Water to provide flood protection in the Green Square area. Through a process of optioneering and hydraulic analysis, a new 2.5 km long underground drain consisting of multiple 1800 mm diameter pipes was installed by microtunnelling, and an open trench box culvert was replaced with channel widening via an anchored retaining wall in the final 300 m from Maddox St to Alexandra Canal. The new drain augments the existing trunk drain system and reduces flood hazard, allowing Australia’s largest urban renewal project to proceed.
The channel widening section of the GSSD was originally intended to be constructed into the bank of the existing open channel. A constructability assessment for installation of the box culvert within the narrow corridor between the existing open channel and adjacent buildings indicated that open trench box culvert construction would not be cost effective. This paper describes an innovative solution, where the existing channel was widened using an anchored retaining wall, replacing the proposed box culverts.
The trenchless (microtunnel) solution offered an alternative, value for money approach with significantly reduced environmental impact and achieved comparatively minimal community disruptions.
This paper also describes the ground engineering challenges and solutions employed on the site which included difficult ground conditions, landfill and addressing impacts of wall construction on adjacent infrastructure such as roads, bridges and buildings. Ground engineering risks were successfully managed through detailed scoping of investigations, numerical modelling of designs and adoption of observational methods during construction. The specification requirements, design, installation, monitoring and performance of the successful microtunnel drain and anchored wall system are discussed.
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Effect of ballast contamination on the behaviour of track substructure
Ballast contamination by subgrade pumping and coal contamination is understood as major cause of track deterioration in many countries over the world. As contamination clogs the ballast voids, the drainage capacity of the track is compromised. Further, lubrication caused by these fines results in reducing load bearing capacity of the ballast layer. In this study, a series of large scale hydraulic conductivity and triaxial tests were performed to study the influence of contamination of ballast on its drainage and shear strength characteristics. Drainage capacity of the contaminated track under different level of contamination was determined, undertaking a numerical analysis using Seep/W. Shear strength of coal and clay contaminated ballast at different confining pressures were compared. Bearing capacity of contaminated track, using ‘foundation under three layers’ method was derived and plotted against the degree of contamination. Subsequently, the critical level of contamination by fouling materials such as clay and coal is discussed on the basis of hydraulic conductivity, shear strength and bearing capacity of the ballast.
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Behaviour of fiber reinforced soil
The increasing value of land and the limited availability of sites for construction are greatly encouraging engineers to considered in situ soil improvement of weak soil deposits. Geotechnical engineers often encounter problems in designing foundations of structures on soft clayey soil. There may be a need for ground treatment to improve the bearing capacity of the soil. In granular soils in situ the soil may be very loose and indicate potential large elastic settlement. Under these conditions soils need to be densified to increase the unit weight and shear strength. The soil at a construction site or part thereof is not always totally suitable for supporting structures. In practice admixtures with fly ash, lime and geogrids are used frequently to stabilize soils and improve their load carrying capacity. Polypropylene fibers have been extensively used in civil engineering applications for many years. These fibers are used in concrete as a three dimensional secondary reinforcement. The influence of randomly oriented polypropylene fiber on the engineering behaviour of soil has not been reported to the same extent. Ease of application and reduction in cost are making this treatment more popular. The purpose of this investigation is to identify and quantify the influence of fiber variables (content and length) on performance of fiber reinforced soil specimens. In this study fibers were mixed with soft clay in various proportions (0%, 0.5%, 1.0%, 1.5% and 2.0%) to investigate the relative strength gained in terms of compaction, CBR, unconfined compression, etc. This paper presents a review of existing experimental and analytical work in this field and identifies other areas needing attention.
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New Approaches to Driven Pile Acceptance
Dr Julian Seidel
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Ground engineering – technology, common sense and good value
In 1985 it took the author a month to run thirty Bishop’s Simplified limit equilibrium slope stability analyses on a personal computer to support the design of remedial works on a medium size embankment dam. Today such an effort would probably be criticised as grossly inadequate (verging on the negligent) since it is not uncommon to execute three hundred, or more, similar calculations using far more sophisticated and accurate algorithms in less than a minute. The paper considers the development and application of technology and advanced analytical tools over the last twenty five years and whether they are being put to good use by adding value to our clients, improving our levels of service or reducing geotechnical risk.
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2D Numerical Evaluation Of A Vertical Soil Nail Wall
The technique of soil nailing has been increasingly used in stabilization works of slopes and excavations. With this, the use of numerical modelling tools in soil nailing projects is becoming increasingly present in Geotechnical companies. This paper includes a case study of a soil nailing wall instrumented in Concepción city, which consists of an excavation of 15 m height in a residual soil of completely decomposed granitic rock. The numerical model was calibrated, comparing the results of the field instrumentation with the numerical estimates provided by the FEM-RS2 software, based on the two-dimensional finite element method and considering an elastic perfectly plastic model. In this way, the strength reduction factor of the geotechnical structure was obtained, which was compared with the overall factor of safety obtained by limit equilibrium analysis. In addition, through the numerical simulation, it was possible to realize an analysis of the loads on the nails, total displacements of the vertical wall, and compare them with the numerical results. The analysis of the results made it possible to confirm the capacity and usefulness of the FEM-RS2 software in the development and elaboration of soil nailing projects.
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Modelling Of Soil Improvement Induced By Tree Root Suction
Vegetation contributes to weak soil stabilisation through reinforcement of the soil, dissipation of excess pore pressures, and increasing the shear strength by induced matric suction. This paper is concerned with the way vegetation influences soil matric suction, shrinkage, and ground settlement. A mathematical model for the rate of root water uptake that considers ground conditions, type of vegetation and climatic parameters, has been developed. Based on this proposed model, the distribution of moisture and the matric suction profile adjacent to the tree are numerically analysed. Field measurements taken from literature are compared with the authors’ numerical model. The predicted results calculated using the soil, plant, and atmospheric parameters implemented in the numerical model, compared favourably with the measured results, justifying the assumptions upon which the model was developed. Furthermore, through the parametric study and sensitivity analysis, the required accuracies of the model parameters are determined. The findings of this study indicate that due to significant reduction in soil moisture content induced by tree roots, the shear strength of the soil will be enhanced.
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The role of proof rolling in pavement construction
Proof rolling of pavement subgrades is a key construction operation for all pavements but despite this there appears to be confusion about the process, the plant used and the evaluation criteria which is leading to subgrades that are adequate being condemned and having to be removed and replaced by stronger materials. The paper looks at the process and whether the plant currently being used as the proof roller is appropriate.