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An overview of engineering geology and geotechnical challenges in the Newcastle Region
The cliff areas along the Newcastle coastline comprise an inter-bedded sequence of sedimentary rocks with layers of variable strength, weathering susceptibility and defect intensity that exert a strong control over cliff morphology and erosion. Coastal cliff line instability in the Newcastle region is predominantly a surface related phenomenon associated with ongoing erosion and degradation processes rather than a deep-seated instability problem. Risk is primarily associated with toppling failure of undercut sandstone blocks, fretting/sloughing of less resistant tuffaceous, shale and coal horizons and erosion of accumulated soil deposits (talus). Sandstone and conglomerate rock falls are predominantly associated with loss of support due to preferential erosion of weaker less durable materials and the presence of occasional low angle joint surfaces. This natural process has been going on for thousands of years and typically results in localised small scale instability problems.
The paper discusses three documented rock falls that have impacted on coastal infrastructure in the last 5 years and outlines the failure mechanisms involved, in particular the role of low angle joints.
Cliff regression along the Newcastle coastline is a process associated with long term slope degradation and erosion as well as periodic localised rock fall events. The paper assesses the rate of long term cliff line regression from literature review, analysis of historical photographs, direct survey and geological interpretation.
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Geological constraints on Mmax values from Western Australia: Implications for seismic hazard assessments
Although Western Australia is commonly viewed as a Stable Continental Region with low rates of earthquake activity, geological and geomorphological evidence indicates that active tectonic processes are occurring. A zone of intraplate transpressional shear (the Western Australia Transpressional Belt—WATB), extends southwest from near Savu Island, Indonesia across the North West Shelf through the Cape Range and the Gascoyne alluvial plain to the Mt. Narryer fault zone (~-27.5˚S). The North West Shelf is accommodating crustal flexure and shallow faulting due to the collision with the Banda Arc, the central west coast exhibits evidence of active fold growth since Marine Oxygen Isotope Stage (MIS) 5e and the Murchison region has evidence of Quaternary tectonic deformation and a record of two large magnitude historical earthquakes.
Geological data to constrain maximum earthquake magnitude (Mmax) estimates for individual seismogenic sources within Stable Continental Regions (SCRs) are lacking. However, within the Stable Continental Region (SCR) of Western Australia, individual morphotectonic structures exist that can be parameterized for inclusion in seismic hazard analyses. Recent studies of the WATB have identified a number of morphotectonics structures that provide structure specific seismic source data. Reverse reactivation of normal faults is manifest as surface expression of faultpropagation folds in the Murchison region. These individual blind-reverse faults are capable of generating earthquakes in the range of Mw6.4-7.4, which is consistent with the largest historically observed earthquake in the region, the 1941 Mw 7.1 Meeberrie event. The rupture of combined fault segments could push these Mmax values up to Mw 7.4-7.7, which would be similar to the 2001 Mw 7.7 Bhuj India event. Ongoing characterization of these features within the WATB has implications for probabilistic seismic hazard analyses (PSHA) in the region. Where these types of structures exist, Mmax estimates may differ from the Mmax values previously suggested in the Brown and Gibson (2004) and Clark et al. (2011) domain models.
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Preloading Ground Improvement For An International Container Terminal Project At Webb Dock Port Melbourne
In this paper, a case study is presented for preloading ground improvement for an automated stacking container development at Port Melbourne, Victoria, a reclaimed site underlain by high compressible marine clays referred to locally as Coode Island Silt (CIS). The paper has firstly reviewed the site reclamation history, followed by consolidation back analysis using PLAXIS 2D to study the historical settlements associated with the previous reclamation and land use and their effect on the future development with and without the adoption of preloading. A decision was then made to adopt a preloading program that involved the application of up to 5.5 m high compacted earth fill (110 kPa which is equivalent to more than twice of the maximum design load for the containers) for a period of 2 to 3 months, targeting to remove over 40% of the potential total settlement under the container stacking loads. The paper also discusses some of the instrumentation, such as settlement plates and vibrating wire piezometers that was employed to verify the target settlement. The study has concluded that the design intention has been achieved by the completed preloading ground improvement program.
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Numerical Study Of Boundary Conditions For Solute Transport Through A Porous Medium
A transition region may be defined as a region of rapid change in medium properties about the interface between two porous media or at the interface between a porous medium and a reservoir. Modelling the transition region between different porous media can assist in the selection of the most appropriate boundary conditions for the standard advection-dispersion equation (ADE). An advantage of modelling the transition region is that it removes the need for explicitly defining boundary conditions, though boundary conditions may be recovered as limiting cases. As the width of a transition region is reduced, the solution of the transition region model (TR model) becomes equivalent to the solution of the standard ADE model with correct boundary conditions. In this paper numerical simulations using the TR model are employed to select the most appropriate boundary conditions for the standard ADE under a variety of configurations and conditions. It is shown that at the inlet boundary between a reservoir and porous medium, continuity of solute mass flux should be used as the boundary condition. At the boundary interface between two porous media both continuity of solute concentration and solute mass flux should be used. Finally, in a finite porous medium where the solute is allowed to advect freely from the exit point, both continuity of solute concentration and solute mass flux should be used as the outlet boundary condition. The findings made here are discussed with reference to a detailed review of previous relevant theoretical and experimental observations.
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Collapse of the Old Pacific Highway, Piles Creek, Somersby
On 8 June 2007 a section of the embankment collapsed along the Old Pacific Highway at Somersby, New South Wales, Australia. The collapse occurred during a heavy rain storm, at a location where three corrugated steel pipes conveyed Piles Creek through the base of the road embankment. Not long after the collapse, a car drove into the resulting void and all the occupants drowned in the flooded creek.
A detailed forensic investigation was undertaken of the Piles Creek site, and also a similar culvert located further along the highway at Leask Creek.
The inverts of the three pipes at Piles Creek had rusted away over their full length.The Leask Creek culverts were displaying some features which were known to have been present prior to the failure at Piles Creek, including loss of the pipe inverts and a depression in the road surface above the culverts. The Leask Creek embankment contained substantial erosion gullies, an active landslip and several voids. These conditions were inferred to be indicative of those likely to have been present at Piles Creek prior to its collapse.
The investigation revealed that the Piles Creek culverts were likely to have been perforated at least six years prior to the final catastrophic failure.
The causes of the failure were the loss of the pipe inverts, and subsequent ground loss into the pipes leading to increased erodibility of the loosened and voided fill, with the collapse triggered by the flood event.
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Structure nonlinearity and response of laterally loaded piles
In light of a generic limiting force profile (LFP), closed-form solutions for laterally loaded free- and fixed- head piles in elastic-plastic media have been developed, and implemented by the first author into a spreadsheet program called GASLFP. The solutions offer an expeditious and sufficiently accurate prediction of response of lateral piles. Conversely, they allow input parameters to be deduced using measured pile response, as has been conducted for over 70 test (elastic) piles to date. Nevertheless, structure nonlinearity of pile body is an important issue at a large deflection.
In this paper, a semi-empirical approach is established to capture pile response owing to structural nonlinearity. Expressions were provided for gaining cracking moment Mcr, flexural rigidity of cracked cross section EpIp, and ultimate bending moment Mult. Against measured response of two laterally loaded single piles, back-estimation indicates that (1) the parameters for elastic piles are quite consistent with the previous findings for piles in sand and clay, (2) The proposed variations of Mcr, EpIp and Mult for nonlinear piles provide good prediction of the pile response against measured data and (3) the modulus of rupture kr of 16.7 (clay) and 33.0(sand) are close to those adopted for structural beams, although a very high kr of 62.7 (thus resulting in higher Mcr) for a pile in sand was deduced (shown elsewhere). The use of the kr for beams would render pile deflections of the later pile to be significantly overestimated. The conclusions may be incorporated into design of laterally loaded piles.
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Mineralogy Of Sydney Building Sandstones In Relation To Geotechnical Properties – 2: Relation Of Quantitative X- Ray Diffraction Data And Cation Exchange Capacity To Geotechnical Indicators Of Rock Durability
The percentages of quartz, feldspar, carbonates and clay minerals in a suite of sandstone samples, evaluated using X-ray powder diffraction techniques and the SIROQUANT data processing system have been compared to a range of geotechnical properties used to evaluate the materials as dimension stones. The total percentage of clay minerals in the sandstones was found to have a relatively strong positive correlation to the dry and wet density of the rock materials, and an inverse or negative correlation to porosity and water absorption, consistent with infilling of otherwise empty pores in a silica-cemented quartz framework by detrital and/or authigenic clay accumulations. Similar relationships to porosity and density are shown by the cation exchange capacity, which has been found in previous studies to be related to the total clay mineral content.
The total proportions of quartz and, where present, feldspar and carbonate minerals, are inversely related to the dry compressive strength of the sandstones, whereas the total proportion of clay minerals shows a positive relationship to dry strength. Quartz, feldspar and carbonate, on the other hand, show a slight positive correlation to the wet compressive strength; the total clay content is negatively related, although again only slightly, to the wet strength values. These relationships are interpreted as representing a contribution to the overall compressive strength by the interstitial clays when the sandstone and its clay minerals are in a dry state, but no contribution by the clays to the compressive strength in wet conditions. The ratio of wet to dry compressive strength, used in some instances as an indicator of sandstone durability, is positively related to the quartz, feldspar and carbonate content, and negatively related to the total proportion of clay minerals determined from either quantitative XRD or from the sandstones’ cation exchange capacity.
Similar relationships exist for dry tensile strength, determined from the modulus of rupture, and hence this property of the sandstones also appears to be increased by cohesion from the interstitial clay minerals. However, unlike compressive strength, the tensile strength in the wet state also decreases slightly with the quartz, feldspar and carbonate content, and increases slightly with the total proportion of clay minerals, suggesting that, in the wet state, the clay minerals retain at least some cohesive effects to influence the tensile strength characteristics. The loss of weight experienced by the sandstones in the sodium sulphate soundness test, on the other hand, seems to show little relation to the mineralogy of the sandstone samples.
These findings confirm that quantitative X-ray diffraction analysis of Sydney sandstones provides results that can be related to key geotechnical parameters of significance to dimension stone applications. Quantitative XRD analysis may therefore be a useful complement to thin section petrographic studies, and also be of value as a simple basis for quality control of geotechnical testing programs or for interpolation of the data from such programs over a wider sample range.
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Geotechnical aspects of the Mid-West Rail Upgrade Project in Western Australia
This paper presents a description of the geotechnical aspects associated with the design and construction of the MidWest Rail Upgrade project in the Mid-West region of Western Australia. It covers aspects of site investigation on existing track formation and track duplication alignments, assessment of the capacity of existing bridge foundations, methods for assessment of the suitability of existing rail formation and upgrades required, analysis of railway behaviour in salt lake areas and recommended ground improvement schemes as well as design of formation-to-bridge transition zones. The paper presents results from a constructability study carried out to assess the stability of existing operational track during the construction of duplicated portions of the line. It also describes the methodology and results of borrow source investigations for both main sections of the project and geotechnical related issues that arose during the construction stage.
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Design And Construction Of An Impermeable Silt Curtain In A Tidal Zone
A new design and construction solution was needed for a sediment remediation project in Homebush Bay, NSW. When faced with the requirement to remove the top 0.5 m thickness of deep very soft sediments containing persistent organic pollutants (including dioxins) and replace this with inert material laid on a geofabric, the ‘traditional’ earth bund coffer dam and/or sheet pile approach had an elevated risk of contaminant migration, and was a significantly more expensive methodology than the Impermeable Silt Curtain (ISC) designed by GHD and constructed/managed by Thiess Services. This is understood to be the first occasion on which an ISC was used for such purposes within a tidal zone (tidal range approximately 2 m). The final constructed length of the ISC was approximately 1100 m. The environmental advantages of this system over the ‘hard’ forms of construction originally proposed included: much less disturbance to the contaminated soft sediments, control of odours by conducting all works beneath water cover and an effective (impermeable) barrier against sediment migration into the bay (not able to be obtained by conventional silt curtains). The design utilised a tough impermeable geotextile, mounted on single piles at regular spacings and bottom weighted by chain link into the underlying ‘muds’. It also included ‘windows’ with flap covers in the top 300 mm, opened at a calculated distance from the dredging/placement work, which allowed tidal water transfer while ensuring that the sediment had settled to a level below the window. The work was a resounding success, albeit it required a high degree of management as part of the design.
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Stabilisation of reactive subgrades by cementitious slurry injection – A review
Slurry Injection Stabilisation is a cost-effective method for the remediation of discrete sections of railtrack subgrade. It is generally applied to subgrade soils that experience fluctuations in strength and volume with varying seasonal moisture contents, thereby undermining the performance of the track. This technique involves the direct injection of cementitious slurry to the subgrade where it reacts with soil particles to enhance the strength and stiffness while decreasing permeability and plasticity.
The aim of the slurry injection operation is to expose as much volume of subgrade soil to chemically active slurry material as possible. The mechanics of slurry infiltration of the subgrade strata and the subsequent reaction of the cementitious additives within the soil mass are two distinct fields of study that influence the scale of subgrade improvement. These fields have been examined in order to develop a comprehensive account of the technical processes involved in the stabilisation technique. This should help the improvement of slurry design and injection procedures to suit site-specific subgrade conditions.