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Geotechnical aspects of the design and construction of temporary works for support of Rail Receival Pit 3 at DBCT
Temporary works were required to support a near vertical excavation of approximately 50 m by 20 m in plan and up to 22 m depth, to allow the construction of a rail inloading pit. Significant constraints were placed on the construction by existing industrial infrastructure and site operations.
The temporary works construction comprised an upper anchored contiguous bored pile wall supporting fill, surficial soils and weathered rock and a lower passive rockbolt support system in the rock beneath the base of the piles. The design of the anchored pile wall and preliminary design of the passive rockbolt system were undertaken on the basis of information gathered during site investigations. The passive rockbolt system was amended and optimised as in situ rock data was obtained and further laboratory testing undertaken. In response to the high risk to the existing infrastructure of collapse the performance of the excavation was monitored by an array of survey monuments, inclinometers and extensometers and compared with modelled behaviour.
Data obtained from monitoring and site readings are presented.
Constructional constraints and the methods used to deal with them are discussed. Logic processes in the probabilistic design of rockbolt support in deep excavations and the interpretation of data obtained are also discussed.
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Digital Twin For Underground Stations: Improving Decision Making For Construction Lifecycle
Challenges in the extraction and use of earth resources and spaces are encountered given a growing worldwide population, rising infrastructures development, and widespread climate change. In Australia, mining and construction are two major bases for economic growth while both being traditional hazardous and heavy industries. A nation-wide infrastructure upgrade featuring large-scale underground development is underway, the geological uncertainties and localisation difficulties of already laid infrastructure are associated with challenges not seen in building construction. A safer and competent subterranean transport solution is yet proposed in the context of sustainable developments. In light of this, geotechnical analysis as a fundamental subject for developing and maintaining safe and sustainable use of underground space has huge potential to be undertaken more intuitively considering the advancements in information management and visualisation. The PhD work examines the state-of-the-art applications, limitations and future opportunities of Building Information Modelling (BIM) and other computational techniques in the digitisation of tunnelling and underground construction. The visualisation and interoperability facilitated by data-driven processes are especially important to underground construction that engages interdisciplinary and multi-environment interaction.
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Use of temporary anchors in reinforced soil wall construction for the M4 Motorway widening
The M4 Motorway has in excess of 100,000 vehicle movements per day with the projection exceeding 150,000 vehicle movements per day by 2030. To facilitate the projected traffic flow increase, the M4 Motorway has been upgraded by adding an additional lane in each direction (eastbound and westbound) to the existing three lanes. The upgrade comprises widening a 7.5 kilometre section of motorway between Parramatta and Homebush including the construction of 2 kilometres of viaduct with 49 spans, 3 bridges and 24 retaining walls (including RSWs, soldier pile walls, soil nail walls and reinforced concrete walls).
This paper focuses on the sections of motorway widened using Reinforced Soil Walls (RSW) and presents a case study of the use of temporary Platipus anchors, to retain up to 9 metres of existing engineered fill embankment of the motorway. The construction of the RSWs required excavation of the existing motorway embankment at between 45° to 75° for excavated heights typically between 6 metres and 9 metres. Platipus anchors were selected in preference to soil nail or sheet pile solution to increase the stability of the steep temporary batter, to expedite the excavation process, reduce the amount of excavation of the embankment and reduce the total construction cost. The design considered the stage excavation process and ensured adequate factor of safety at each stage of the excavation process. In addition, the design confirmed that the settlement of the existing M4 pavement immediately adjacent to the excavation was within tolerable limits.
The paper provides discussion on the feasibility assessment of the use of the ‘Platipus’ anchors and the design undertaken for the temporary retention system. It also provides a discussion on the installation process for the anchors, anchor testing undertaken, instrumentation and monitoring; and construction challenges for integration of the temporary support into the permanent works.
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Significance of considering soil-structure interaction effects on seismic design of unbraced building frames resting on soft soils
The current study carries out a comprehensive critical review on available and well-known research studies in the area of seismic behaviour of braced and unbraced building structures affected by soil-structure interaction (SSI). Based on the current review outcomes, it has become apparent that considering effects of SSI in seismic design of braced building structures is not necessary and assuming fixed-base structure is deemed to be conservative. However, SSI effects can amplify the lateral deflections and corresponding inter-storey drifts of unbraced building structures founding on soft grounds, forcing the structure to behave in the inelastic range, resulting in severe damage of the building structures. Consequently, seismic design procedure of unbraced building structures founding on soft soils without taking into account detrimental influences of SSI cannot adequately assure structural sufficiency and safety for the benefit of the community.
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Disposal of stormwater runoff by soakage in Perth, Western Australia
Extensive use is made in Perth of soakage basins (referred to locally as sumps) for the disposal of runoff from roads in urban areas and soak wells for the disposal of roof runoff. Software packages such as PCSUMP, INFIL and MODRET as well as “rules of thumb” have been used to design the soakage basins. This paper discusses the advantages and disadvantages of these design software packages as well as presenting a new simplified design method. Methods of assessing soil permeability and other considerations in the design of sumps and soak wells are presented together with advice on related issues including cracking of houses near sumps and proximity of sumps to bridge foundations.
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A new application of radar in improving pile dynamic formulae used in the quality control of pile foundations
Installing piles into the ground is a very complex if not uncertain activity. This is particularly true from the point of view of proofing piled foundations. One of the methods currently available is the Dynamic or Energy Formulae that are the oldest and frequently used formulae in determining the bearing capacity of piles. The more recent methods are based on the Wave Equation Analysis and different formulations such as Case Method, TNOWave, CAPWAP® and TEPWAP were developed for pre-driving analysis and post-driving measurement applications. The energy or dynamic formulae, which were developed based on the Newtonian Impact theory, have been regarded as being unreliable and less accurate than the more analytical Wave Equation Analysis methods. The two main reasons for the poor performance of the dynamic formulae are that the hammer energy is assumed and that they do not take the dynamic resistance into account. The advent of new technologies in the construction industry has produced gradual improvements that have resulted in the dynamic method to be used on many projects with greater reliability. In this paper, a new application of radar called IBIS-S is proposed as well as site test results are presented using the Hiley, Gates and MnDOT formulae. The comparison of the results with the more rigorous PDA, CAPWAP® and the GRLWEAP™ analysis show that with the application of new and precise testing equipments, the dynamic formula can be used with greater accuracy than the Case method. It is also shown that the IBIS-S unit may also be used to estimate and evaluate the empirical parameters used in the CAPWAP® and GRLWEAP™ analysis. This approach enables evaluation of the pile capacity to be made more accurately using the dynamic equations.
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Design And Construction Of Roma Street Station Cavern, Cross River Rail, Brisbane
The new Roma Street underground railway station in Brisbane is being constructed as part of Cross River Rail’s Tunnel, Stations and Development (TSD) package. The joint venture of CPB Contractors, BAM International Australia, Ghella and UGL (CBGU JV) is building the 5.9km long twin tunnels from the Southern Tunnel Portal near Dutton Park station, beneath the Brisbane River and CBD to the Northern Tunnel Portal in Spring Hill. The Cross River Rail project includes excavation and construction of four new underground stations.
Roma Street station comprises a 280m long cavern, five smaller connecting tunnels (adits) and three shafts. The station cavern has an excavated span of up to 24.4m with approximately 15m rock cover. It has been excavated within the Neranleigh-Fernvale Group (NFG) rock mass, which comprises weakly metamorphosed sandstone (meta-greywacke and arenite), phyllite and subordinate quartzite and meta-basalt. The station lies within the regional Normanby Fault Zone, characterised by a major fault up to 20m wide comprising a combination of intact rock, rock breccia and clay gouge. The fault zone encountered during the station cavern excavation required heavier primary support and localised foundation treatment.
The initial primary (temporary) support of the cavern and adits comprised rock bolts, cable bolts and a thin synthetic fibre-reinforced shotcrete lining. In some areas a passive shotcrete arch lining was required. Overlying piled footings from an existing busway overpass structure were within a metre of the adits’ excavated profile which necessitated a complex load transfer structure at the surface and verification of pile toe levels during tunnel construction.
The cavern permanent lining typically comprises steel fibre-reinforced concrete in the crown, bar reinforced concrete for the sidewalls, and bar and steel fibre-reinforced concrete invert slabs. Bar reinforcement is used in the cavern crown where it intersects the adits. Ground loads for the permanent structure had to consider the influence of future developments.
This paper presents some of the challenges of the primary support and permanent lining design of the station cavern and adits. It summarises the as-encountered ground conditions, aspects of the primary support and permanent lining design that were geotechnically challenging and the solutions developed to meet the project requirements.
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Conceptual model of residual friction in Montmorillonitic soils at large void ratios
In soil mechanics, friction is usually included in a mathematical model as a ‘friction coefficient’ (or angle of internal friction). Conventional geotechnical testing equipment is employed to experimentally define the friction coefficient for a soil. A friction coefficient estimated in this way is a macroscopic parameter representing the integrated effects of many dissipative processes occurring at the microscale. For this reason, conventional geotechnical testing cannot be expected to give any substantial insight into the microscale processes leading to the frictional behaviour observed for soils. Traditional ideas advanced about the frictional behaviour of soils are motivated by observations of the shear strength of dry particle assemblies like sand and gravel. It is shown here that these ideas are not applicable to platy clay soils with well-developed diffuse-double layers at a residual friction state. This provides the foundation for the presentation of a new conceptual theory of energy dissipation in saturated montmorillonite clay soils at the residual friction angle. While the proposed theory is still in its infancy (and there are a number of unresolved issues), it is clear that the theory provides a basis for a deeper understanding of the behaviour of saturated montmorillonitic soils at the residual friction angle. The new theory is based upon a number of assumptions and hypotheses that can be systematically studied experimentally and numerically, and so the theory provides a framework for a systematic experimental and numerical program of investigation.
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Design Of Slope Stabilizing Piles For Reinforced Soil Walls On Hunter Expressway
The Hunter Expressway will provide a 40 km long four-lane divided carriageway motorway between the F3 Interchange at Newcastle and the New England Highway at Branxton, New South Wales Australia. The project is due to be opened by the end of 2013. The Hunter Expressway Alliance (HEA), comprising Roads and Maritime Services (RMS), Thiess Pty Ltd, Parsons Brinckerhoff and Hyder Consulting, is responsible for the design and construction of the 13 km eastern section of new freeway and local road adjustments. There are 28 bridges and major culvert structures and 29 Reinforced Soil Walls (RSWs). This paper discusses the design challenges faced by the RSW designers and the innovative engineering solution developed for RW17, a 120 m long RSW up to 10m in height on sloping ground with foundations containing bands of low strength tuffaceous claystone. To achieve the minimum design factor of safety (FOS) of 1.35 for the overall slope stability of the RSW as stipulated in RMS Specification R57, three rows of 450 mm/750 mm diameter and one row of 1500 mm diameter bored piles were designed and adopted at various selected sections along the 120 m long slope. Both the limit equilibrium program Slope/W and the finite element program PLAXIS were used to assess the FOS for the global stability of the RSW, ground movements during and after RSW construction and forces in the piles. Two inclinometers were installed to monitor the field lateral ground movements during and after construction to verify the design assumptions. This paper describes the challenging ground conditions, the development of the stabilising pile design, the analytical models used and the results of the construction phase monitoring of the completed RSW.
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Are we modelling the wrong pile? – Is it time to improve pile testing analysis?
The majority of cast in-situ pile load testing for resistance verification is undertaken using high strain dynamic testing where a hammer strikes the top of a pile, imparting a one-dimensional stress wave down the pile. This ‘stress wave’ is captured using strain and accelerometer gauges to produce force and velocity readings, which are equal when the velocity is multiplied by the pile impedance. The impedance is a function of concrete modulus, concrete wave speed and cross- sectional area. Case Pile Wave Analysis Program (CAPWAP) is signal matching software where the captured force and velocity data are analysed to determine the static soil resistance with respect to the pile head deflection. CAPWAP is a numerical analysis program where the pile is divided into a series of segments, each with individually uniform properties (Impedance). For prefabricated piles, such as reinforced precast, or prestressed concrete, the impedance is uniform for the full length. However, for bored piles, the cross-sectional area can vary with depth, and hence the impedance can vary significantly, especially in soft soils. In many cases, the pile model used in a CAPWAP analysis is not adjusted to reflect the as-constructed pile geometry and only the pile impedance is modified or guessed. Effectively, this is trying to model the static resistance of a pile with a pile model that is not geometrically accurate. This approach to modelling without an accurate pile model can lead to an overestimation of static resistance. There is now technology readily available that can assist with determining the actual cross-sectional area over the full depth of the pile. This paper presents the comparisons of using design vs actual cross-sectional area profiles in soft soil environments. Modelling the actual area increase can lead to more accurate and representative shaft resistance determination.