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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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Analytical Modelling Of Pavements Under Moving Loads
On a global scale, substantial financial resources are allocated for developing safe roads and the maintenance of existing ones. As a result, it is desirable to ensure there is no unnecessary spending and that allocated budgets are utilised as efficiently as possible. Conventionally, analytical pavement design and analysis takes place through the development of an axi-symmetric solution. These models are based on making several assumptions as well as transforming a given problem into an axi-symmetric system, which simplifies and undermines the accuracy of output that is achieved. CIRCLY is an example of a software package that evaluates pavement parameters through the utilisation of axisymmetric solutions. In making these mathematical simplifications, models become restricted to axi-symmetric systems, stationary loads (i.e. a moving coordinate system is not considered), and static cases as the effects due to inertia are ignored. To eliminate these constraints, this paper aims to develop an alternative analytical approach which can be used to efficiently and accurately determine pavement responses under stationary and moving loads. The governing equation that forms the basis of the model is Cauchy’s theorem for examining the deformation characteristics of a pavement structure. Several substitutions and simplifications have been made in order to incorporate a moving coordinate system and to transform Cauchy’s theorem to a relationship that is entirely based on displacements. This will then allow for the calculation of associated stresses and strains. The relationship developed is solved through the utilisation of Fourier transformations and complex numbers, which is the main focus of this paper. Based on the derivations and associated formulations, a program has been developed which can be used to calculate solutions for flexible pavements under variable loading conditions. Several case studies have been carried out and the output analysed. It was concluded that, the method is able to address the assumptions made in conventional analytical models. Additionally, the program is capable of accurately carrying out calculations at substantially reduced computational effort, a main restriction that is encountered with numerical approaches.
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Numerical prediction of response of circular footings on structured soils
The Structured Cam Clay (SCC) model was incorporated in a finite element program to study the influence of soil structure in the settlement of a circular footing. The SCC model has three parameters in addition to Modified Cam Clay. These parameters show the effect of structure on the stress-strain response of soils. A parametric finite element analysis was conducted to investigate the effect of each of these parameters on the pressure-displacement response of a circular footing resting on structured soil. The investigation shows that principal effect of SCC parameters is on the plastic slope of the pressure displacement response of the footing resting on structured soil.
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A Cylindrical Model Of Pyrite Oxidation In Coastal Acidic Soils
Detailed analyses of acid soils in coastal areas of (New South Wales, NSW) indicate that (FeS2) oxidation occurs very close to narrow root channels. The root channels have been caused by extant organic activity and allow oxygen to diffuse through to pyritic layers. From the wall of the root channels in the pyritic layers, oxygen diffuses laterally into the acid soil matrix oxidizing the pyrite present. Such a simultaneous process can be modeled cylindrically. In this paper, a new cylindrical model is developed and solved using approximations to pyrite consumption kinetics. An adapted PDE2D code based on finite element methods is used to solve a linear approximation and Michaelis-Menten uptake kinetics. Pyrite oxidation produces acid in the soil matrix that is subsequently transported to the estaurine waterways, following high rainfall sessions causing a number of environmental disasters. An estimate of the new acid produced in the field is often required before remediation work is possible, and such an estimate may be determined easily using the new model. The result of pyrite oxidation based on the cylindrical approach demonstrate that the new model can accurately predict pyrite oxidation and acid production. The total acid production calculated using the new approach was found to be close to the actual field amount at the Berry site. The new results also compare well with the predictions made by the previous models developed for the Berry site.
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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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Retaining Structures Performance Against Seismic Loads For Australian Type Ground Motions
The conventional design of retaining structures against seismic loads is based on the Mononobe Okabe type design rules that are specified in many international seismic codes. Attempts had been made by researchers to apply these rules to a range of retaining walls. However, the problem with these conventional methods is that they are grounded in highly seismic area type ground motions which have considerably different frequency content to Australian type ground motions.
This paper presents the results of dynamic time history analyses of gravity retaining walls subjected to Australian type earthquake ground motion. These are based on FLAC non-linear dynamic modelling of a range of retaining walls (e.g. bridge abutments, etc). Comparisons are made with results of conventional Mononobe Okabe type design rules for retaining walls with varying lateral and bending stiffnesses.
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State dependent dilatancy relationship for sands
The stress dilatancy relation which accounts for the dependencies on stress level and density is proposed. The consideration of these aspects would give a significant implication on the modelling of granular materials behaviour since it is mostly dominated by the evolution of dilatancy and density history. Modified Cam clay dilatancy is modified through state index parameter Is proposed by Verdugo (1992) which measures the ratio between the deviation of the current void ratio and its relative critical void ratio to a reference one. The proposed stress dilatancy relation is compared to the experimental result from undrained triaxial test for wide range density and stress level. It also indeed exhibits a special case of general anisotropic dissipation function introduced by Dafalias (1986).
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Databases and data-centric geotechnics
2023 Harry Poulos Award and Lecture
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Databases and data-centric geotechnics
2023 Harry Poulos Award and Lecture