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Implementing The AGS Landslide Risk Management Guidelines In A Municipal Planning Scheme – A Case Study In The Colac Otway Shire, Victoria
The Colac Otway Shire in south west Victoria are in the process of amending their Planning Scheme to include landslide risk assessment for new developments in landslide prone areas. The amendment is primarily intended to limit the Shire’s liability and will require consultants to assess risk using the Australian Geomechanics guidelines on landslide risk management. However data limitations, particularly the paucity of historical information on landslide events, have precluded landslide hazard mapping for all types of landslides and their likelihood of occurrence, at the site-scale required for planning controls. The solution adopted was to extend the Erosion Management Overlay to cover all areas of the Shire in which landslides are credible, and the implementation of a documented process to determine when a landslide risk assessment for any development is required. The process includes reference to existing information stored on a GIS database, a checklist for use in an initial site visit by the Shire, specific requirements for consultant’s reports, and information checking and mediation processes for the Shire. The limited landslide risk management experience of the Shire planners and some small and medium-scale consulting companies has highlighted a local desire for a more prescriptive code.
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Repetitive Dynamic Loading Of Soils And Highly Weathered Rocks Due To Foreshore Construction Activities
Rockwall construction work was carried out on the foreshore of Port Phillip Bay at Mount Eliza in 1995 involving the delivery of many truckloads of boulders, the mass of each boulder generally being in the range of 0.8 to 3 tonnes. After being dumped onto the beach from tip-trucks, these boulders were then individually placed either in rockwalls at the back of the beach or dropped onto the beach sand to form a seawall for erosion protection purposes. Nearby residents complained that the foreshore construction activities generated noticeable ground vibrations at their houses. The occupants of one house, located 95 metres (m) from the point where trucks were dumping their loads of boulders, reported that hanging objects in the house were set swinging by the vibrations, which also could be distinctly felt when lying on lounges and beds within the house. The ground vibrations generated by the 1995 foreshore construction works were not monitored at that time, but on 13th November 1998 the 1995 foreshore works were replicated and monitored, so as to determine the magnitude of the resulting ground vibrations and their attenuation with increasing distance.
The 1995 works continued over a period of several weeks. The repetitive nature of the vibrations, involving about one hundred significant dynamic loadings each day, raised the possibility of fatigue weakening of the soils and highly weathered rocks in the cliffs behind the foreshore. The soils and highly weathered rocks in the area have unconfined compressive strengths less than 250 kPa. The adjacent cliff developed tension cracks just behind its crest, prior to completion of the foreshore construction works in June 1995, and failed on 8th July 1995. The cliff was not instrumented at the time of failure and hence the precise cause(s) of failure remain a matter of opinion. The aim of the 1998 test work was to ascertain if the vibrations generated by these foreshore construction works were sufficiently powerful for fatigue weakening to be a feasible, contributory failure mechanism for the cliff.
Comprehensive description of vibration requires measurement of the amplitude and frequency of the ground motion, and how these parameters vary over time, ie recording of a time series of the vibration rather than just the peak particle velocity. This allows for the recordings to be decomposed using Fourier analysis to show the frequency composition and additionally allows for conversion by differentiation or integration between displacement, velocity and acceleration. The ground vibration from each of the 1998 tests described in this paper was recorded as a time series.
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Simplified Excavation-Induced Lateral Displacement Assessment in Sydney Area
Excavations change the stress state of the in-situ ground. The altered stress state causes lateral and vertical displacement in the buildings and structures adjacent to the excavation. In areas like the Sydney region, tectonic locked-in horizontal stresses at shallow depth exceed the vertical stress and the high in-situ horizontal stresses cause possibility of excavation- induced displacement in good quality rocks (e.g., Hawkesbury Sandstone Class I, II, and III).
This paper estimates the magnitude and shape of the excavation-induced displacement trough along the excavation edge in Hawkesbury Sandstone. A parametric study was undertaken using three-dimensional finite element analysis to estimate the maximum lateral excavation-induced displacement as well as the lateral displacement trough as a function of the ground type, excavation depth and width, and principal in-situ stress orientation. The results were verified by comparing with monitoring results published for Sydney Sandstone.
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AGS Brisbane Symposium 2024
Geotechnical Ingenuity for a Sustainable Future
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Geotechnical aspects of a drainage culvert
This paper describes the geotechnical aspects of the design and construction of a transverse drainage culvert constructed in Goodna to help alleviate flood backwash. Goodna was one of the worst hit areas in the Queensland floods of January 2011. The culvert involved the construction of three pit structures, pipe jacking between these pits and towards the Brisbane River, and slope stabilisation works at the outlet. The design and construction issues associated with the deep excavations, pipe jacking, pile installation, anchor installation and testing and revetment have been discussed.
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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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West Australian Geotechnics and Geology
AGS WA 2020 Symposium
Russell Clayton, Prof. Barry Lehane, Eric Hudson-Smith and Alison Jennings
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A new ring shear apparatus for the determination of the residual shear resistance of remoulded brown coal
Victorian brown coal is a typical intermediate geomaterial, whose behaviour falls between that of soft rock and engineering clay. The intact material exhibits lower permeability and higher tensile strength compared to overconsolidated clay. Large, shallow open cuts are used to mine the coal in the Latrobe Valley, Victoria, Australia, predominantly as fuel for Victoria’s power stations. For batter design the brown coal is treated as clay with high values of cohesion and friction angle. Composite rotational and block sliding is a recognised failure mode for this material and it is apparent from recent observations that failure risk increases with time. During long-term movements of the brown coal behind and below the batters it is anticipated that the material will be crushed and remoulded along sliding surfaces as a result of progressive pre-failure displacements. After periods of decades, the assumption is that for large sections along any incipient failure surface, shear strength will be at or close to the residual shear strength of the material. Thus. it is important to understand whether this assertion is correct and the processes leading to the weakened state. A new ring-shear test apparatus has been designed to determine the variation of shear strength of this material for a range of shear strains under essentially drained conditions. In this paper the design considerations and the resulting form of the test apparatus are presented. The equipment is also applicable to the testing of the interseam clays, silts and fine sands that are also found in the mines.
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What is the total suction of soil at oven dry?
The values of total suction (moisture potential) ascribed to the oven dry condition by various authors are reviewed. An explicit calculation of the limiting total suction imposed by a drying oven is described. The variables are the oven temperature together with the relative humidity and temperature of the ambient air that is necessarily admitted into the oven. The calculation requires reference to psychrometric relationships between relative humidity, temperature and humidity ratio. These relationships are accessible in commonly available psychrometric charts as well as in other forms. For typical laboratory conditions, the limiting total suction imposed by a drying oven will fall in the range 5.8 to 6.0 logkPa (6.8 to 7.0 pF). The direction and magnitude of the change in total suction that occurs when an oven dried soil sample cools from oven temperature to room temperature is also considered by reference to published experimental data and the known temperature trends of the physical phenomena associated with suction. A small set of experimental measurements of the humidity over soil samples cooled from near oven dry to room temperature are reported. These experiments were aimed at the narrow question of the direction and magnitude of the change in the soil suction upon cooling from drying oven temperature. Some published data on the suction attained when a soil is dried to zero moisture content by a room temperature process are also reviewed.